diff --git a/Data/BitUtil.hs b/Data/BitUtil.hs
new file mode 100644
--- /dev/null
+++ b/Data/BitUtil.hs
@@ -0,0 +1,71 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE MagicHash #-}
+#endif
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.BitUtil
+-- Copyright   :  (c) Clark Gaebel 2012
+--                (c) Johan Tibel 2012
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+-----------------------------------------------------------------------------
+
+module Data.BitUtil
+    ( highestBitMask
+    , shiftLL
+    , shiftRL
+    ) where
+
+-- On GHC, include MachDeps.h to get WORD_SIZE_IN_BITS macro.
+#if defined(__GLASGOW_HASKELL__)
+# include "MachDeps.h"
+#endif
+
+import Data.Bits ((.|.), xor)
+
+#if __GLASGOW_HASKELL__
+import GHC.Exts (Word(..), Int(..))
+import GHC.Prim (uncheckedShiftL#, uncheckedShiftRL#)
+#else
+import Data.Word (shiftL, shiftR)
+#endif
+
+-- The highestBitMask implementation is based on
+-- http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+-- which has been put in the public domain.
+
+-- | Return a word where only the highest bit is set.
+highestBitMask :: Word -> Word
+highestBitMask x1 = let x2 = x1 .|. x1 `shiftRL` 1
+                        x3 = x2 .|. x2 `shiftRL` 2
+                        x4 = x3 .|. x3 `shiftRL` 4
+                        x5 = x4 .|. x4 `shiftRL` 8
+                        x6 = x5 .|. x5 `shiftRL` 16
+#if !(defined(__GLASGOW_HASKELL__) && WORD_SIZE_IN_BITS==32)
+                        x7 = x6 .|. x6 `shiftRL` 32
+                     in x7 `xor` (x7 `shiftRL` 1)
+#else
+                     in x6 `xor` (x6 `shiftRL` 1)
+#endif
+{-# INLINE highestBitMask #-}
+
+-- Right and left logical shifts.
+shiftRL, shiftLL :: Word -> Int -> Word
+#if __GLASGOW_HASKELL__
+{--------------------------------------------------------------------
+  GHC: use unboxing to get @shiftRL@ inlined.
+--------------------------------------------------------------------}
+shiftRL (W# x) (I# i) = W# (uncheckedShiftRL# x i)
+shiftLL (W# x) (I# i) = W# (uncheckedShiftL#  x i)
+#else
+shiftRL x i   = shiftR x i
+shiftLL x i   = shiftL x i
+#endif
+{-# INLINE shiftRL #-}
+{-# INLINE shiftLL #-}
diff --git a/Data/Graph.hs b/Data/Graph.hs
new file mode 100644
--- /dev/null
+++ b/Data/Graph.hs
@@ -0,0 +1,478 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE Rank2Types #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Graph
+-- Copyright   :  (c) The University of Glasgow 2002
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
+--
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- A version of the graph algorithms described in:
+--
+--   /Structuring Depth-First Search Algorithms in Haskell/,
+--   by David King and John Launchbury.
+--
+-----------------------------------------------------------------------------
+
+module Data.Graph(
+
+        -- * External interface
+
+        -- At present the only one with a "nice" external interface
+        stronglyConnComp, stronglyConnCompR, SCC(..), flattenSCC, flattenSCCs,
+
+        -- * Graphs
+
+        Graph, Table, Bounds, Edge, Vertex,
+
+        -- ** Building graphs
+
+        graphFromEdges, graphFromEdges', buildG, transposeG,
+        -- reverseE,
+
+        -- ** Graph properties
+
+        vertices, edges,
+        outdegree, indegree,
+
+        -- * Algorithms
+
+        dfs, dff,
+        topSort,
+        components,
+        scc,
+        bcc,
+        -- tree, back, cross, forward,
+        reachable, path,
+
+        module Data.Tree
+
+    ) where
+
+#if __GLASGOW_HASKELL__
+# define USE_ST_MONAD 1
+#endif
+
+-- Extensions
+#if USE_ST_MONAD
+import Control.Monad.ST
+import Data.Array.ST (STArray, newArray, readArray, writeArray)
+#else
+import Data.IntSet (IntSet)
+import qualified Data.IntSet as Set
+#endif
+import Data.Tree (Tree(Node), Forest)
+
+-- std interfaces
+import Control.Applicative
+import Control.DeepSeq (NFData(rnf))
+import Data.Maybe
+import Data.Array
+import Data.List
+
+-------------------------------------------------------------------------
+--                                                                      -
+--      External interface
+--                                                                      -
+-------------------------------------------------------------------------
+
+-- | Strongly connected component.
+data SCC vertex = AcyclicSCC vertex     -- ^ A single vertex that is not
+                                        -- in any cycle.
+                | CyclicSCC  [vertex]   -- ^ A maximal set of mutually
+                                        -- reachable vertices.
+
+instance NFData a => NFData (SCC a) where
+    rnf (AcyclicSCC v) = rnf v
+    rnf (CyclicSCC vs) = rnf vs
+
+instance Functor SCC where
+    fmap f (AcyclicSCC v) = AcyclicSCC (f v)
+    fmap f (CyclicSCC vs) = CyclicSCC (fmap f vs)
+
+-- | The vertices of a list of strongly connected components.
+flattenSCCs :: [SCC a] -> [a]
+flattenSCCs = concatMap flattenSCC
+
+-- | The vertices of a strongly connected component.
+flattenSCC :: SCC vertex -> [vertex]
+flattenSCC (AcyclicSCC v) = [v]
+flattenSCC (CyclicSCC vs) = vs
+
+-- | The strongly connected components of a directed graph, topologically
+-- sorted.
+stronglyConnComp
+        :: Ord key
+        => [(node, key, [key])]
+                -- ^ The graph: a list of nodes uniquely identified by keys,
+                -- with a list of keys of nodes this node has edges to.
+                -- The out-list may contain keys that don't correspond to
+                -- nodes of the graph; such edges are ignored.
+        -> [SCC node]
+
+stronglyConnComp edges0
+  = map get_node (stronglyConnCompR edges0)
+  where
+    get_node (AcyclicSCC (n, _, _)) = AcyclicSCC n
+    get_node (CyclicSCC triples)     = CyclicSCC [n | (n,_,_) <- triples]
+
+-- | The strongly connected components of a directed graph, topologically
+-- sorted.  The function is the same as 'stronglyConnComp', except that
+-- all the information about each node retained.
+-- This interface is used when you expect to apply 'SCC' to
+-- (some of) the result of 'SCC', so you don't want to lose the
+-- dependency information.
+stronglyConnCompR
+        :: Ord key
+        => [(node, key, [key])]
+                -- ^ The graph: a list of nodes uniquely identified by keys,
+                -- with a list of keys of nodes this node has edges to.
+                -- The out-list may contain keys that don't correspond to
+                -- nodes of the graph; such edges are ignored.
+        -> [SCC (node, key, [key])]     -- ^ Topologically sorted
+
+stronglyConnCompR [] = []  -- added to avoid creating empty array in graphFromEdges -- SOF
+stronglyConnCompR edges0
+  = map decode forest
+  where
+    (graph, vertex_fn,_) = graphFromEdges edges0
+    forest             = scc graph
+    decode (Node v []) | mentions_itself v = CyclicSCC [vertex_fn v]
+                       | otherwise         = AcyclicSCC (vertex_fn v)
+    decode other = CyclicSCC (dec other [])
+                 where
+                   dec (Node v ts) vs = vertex_fn v : foldr dec vs ts
+    mentions_itself v = v `elem` (graph ! v)
+
+-------------------------------------------------------------------------
+--                                                                      -
+--      Graphs
+--                                                                      -
+-------------------------------------------------------------------------
+
+-- | Abstract representation of vertices.
+type Vertex  = Int
+-- | Table indexed by a contiguous set of vertices.
+type Table a = Array Vertex a
+-- | Adjacency list representation of a graph, mapping each vertex to its
+-- list of successors.
+type Graph   = Table [Vertex]
+-- | The bounds of a 'Table'.
+type Bounds  = (Vertex, Vertex)
+-- | An edge from the first vertex to the second.
+type Edge    = (Vertex, Vertex)
+
+-- | All vertices of a graph.
+vertices :: Graph -> [Vertex]
+vertices  = indices
+
+-- | All edges of a graph.
+edges    :: Graph -> [Edge]
+edges g   = [ (v, w) | v <- vertices g, w <- g!v ]
+
+mapT    :: (Vertex -> a -> b) -> Table a -> Table b
+mapT f t = array (bounds t) [ (,) v (f v (t!v)) | v <- indices t ]
+
+-- | Build a graph from a list of edges.
+buildG :: Bounds -> [Edge] -> Graph
+buildG bounds0 edges0 = accumArray (flip (:)) [] bounds0 edges0
+
+-- | The graph obtained by reversing all edges.
+transposeG  :: Graph -> Graph
+transposeG g = buildG (bounds g) (reverseE g)
+
+reverseE    :: Graph -> [Edge]
+reverseE g   = [ (w, v) | (v, w) <- edges g ]
+
+-- | A table of the count of edges from each node.
+outdegree :: Graph -> Table Int
+outdegree  = mapT numEdges
+             where numEdges _ ws = length ws
+
+-- | A table of the count of edges into each node.
+indegree :: Graph -> Table Int
+indegree  = outdegree . transposeG
+
+-- | Identical to 'graphFromEdges', except that the return value
+-- does not include the function which maps keys to vertices.  This
+-- version of 'graphFromEdges' is for backwards compatibility.
+graphFromEdges'
+        :: Ord key
+        => [(node, key, [key])]
+        -> (Graph, Vertex -> (node, key, [key]))
+graphFromEdges' x = (a,b) where
+    (a,b,_) = graphFromEdges x
+
+-- | Build a graph from a list of nodes uniquely identified by keys,
+-- with a list of keys of nodes this node should have edges to.
+-- The out-list may contain keys that don't correspond to
+-- nodes of the graph; they are ignored.
+graphFromEdges
+        :: Ord key
+        => [(node, key, [key])]
+        -> (Graph, Vertex -> (node, key, [key]), key -> Maybe Vertex)
+graphFromEdges edges0
+  = (graph, \v -> vertex_map ! v, key_vertex)
+  where
+    max_v           = length edges0 - 1
+    bounds0         = (0,max_v) :: (Vertex, Vertex)
+    sorted_edges    = sortBy lt edges0
+    edges1          = zipWith (,) [0..] sorted_edges
+
+    graph           = array bounds0 [(,) v (mapMaybe key_vertex ks) | (,) v (_,    _, ks) <- edges1]
+    key_map         = array bounds0 [(,) v k                       | (,) v (_,    k, _ ) <- edges1]
+    vertex_map      = array bounds0 edges1
+
+    (_,k1,_) `lt` (_,k2,_) = k1 `compare` k2
+
+    -- key_vertex :: key -> Maybe Vertex
+    --  returns Nothing for non-interesting vertices
+    key_vertex k   = findVertex 0 max_v
+                   where
+                     findVertex a b | a > b
+                              = Nothing
+                     findVertex a b = case compare k (key_map ! mid) of
+                                   LT -> findVertex a (mid-1)
+                                   EQ -> Just mid
+                                   GT -> findVertex (mid+1) b
+                              where
+                                mid = (a + b) `div` 2
+
+-------------------------------------------------------------------------
+--                                                                      -
+--      Depth first search
+--                                                                      -
+-------------------------------------------------------------------------
+
+-- | A spanning forest of the graph, obtained from a depth-first search of
+-- the graph starting from each vertex in an unspecified order.
+dff          :: Graph -> Forest Vertex
+dff g         = dfs g (vertices g)
+
+-- | A spanning forest of the part of the graph reachable from the listed
+-- vertices, obtained from a depth-first search of the graph starting at
+-- each of the listed vertices in order.
+dfs          :: Graph -> [Vertex] -> Forest Vertex
+dfs g vs      = prune (bounds g) (map (generate g) vs)
+
+generate     :: Graph -> Vertex -> Tree Vertex
+generate g v  = Node v (map (generate g) (g!v))
+
+prune        :: Bounds -> Forest Vertex -> Forest Vertex
+prune bnds ts = run bnds (chop ts)
+
+chop         :: Forest Vertex -> SetM s (Forest Vertex)
+chop []       = return []
+chop (Node v ts : us)
+              = do
+                visited <- contains v
+                if visited then
+                  chop us
+                 else do
+                  include v
+                  as <- chop ts
+                  bs <- chop us
+                  return (Node v as : bs)
+
+-- A monad holding a set of vertices visited so far.
+#if USE_ST_MONAD
+
+-- Use the ST monad if available, for constant-time primitives.
+
+newtype SetM s a = SetM { runSetM :: STArray s Vertex Bool -> ST s a }
+
+instance Monad (SetM s) where
+    return x     = SetM $ const (return x)
+    {-# INLINE return #-}
+    SetM v >>= f = SetM $ \s -> do { x <- v s; runSetM (f x) s }
+    {-# INLINE (>>=) #-}
+
+instance Functor (SetM s) where
+    f `fmap` SetM v = SetM $ \s -> f `fmap` v s
+    {-# INLINE fmap #-}
+
+instance Applicative (SetM s) where
+    pure x = SetM $ const (return x)
+    {-# INLINE pure #-}
+    SetM f <*> SetM v = SetM $ \s -> f s >>= (`fmap` v s)
+    -- We could also use the following definition
+    --   SetM f <*> SetM v = SetM $ \s -> f s <*> v s
+    -- but Applicative (ST s) instance is present only in GHC 7.2+
+    {-# INLINE (<*>) #-}
+
+run          :: Bounds -> (forall s. SetM s a) -> a
+run bnds act  = runST (newArray bnds False >>= runSetM act)
+
+contains     :: Vertex -> SetM s Bool
+contains v    = SetM $ \ m -> readArray m v
+
+include      :: Vertex -> SetM s ()
+include v     = SetM $ \ m -> writeArray m v True
+
+#else /* !USE_ST_MONAD */
+
+-- Portable implementation using IntSet.
+
+newtype SetM s a = SetM { runSetM :: IntSet -> (a, IntSet) }
+
+instance Monad (SetM s) where
+    return x     = SetM $ \s -> (x, s)
+    SetM v >>= f = SetM $ \s -> case v s of (x, s') -> runSetM (f x) s'
+
+instance Functor (SetM s) where
+    f `fmap` SetM v = SetM $ \s -> case v s of (x, s') -> (f x, s')
+    {-# INLINE fmap #-}
+
+instance Applicative (SetM s) where
+    pure x = SetM $ \s -> (x, s)
+    {-# INLINE pure #-}
+    SetM f <*> SetM v = SetM $ \s -> case f s of (k, s') -> case v s' of (x, s'') -> (k x, s'')
+    {-# INLINE (<*>) #-}
+
+run          :: Bounds -> SetM s a -> a
+run _ act     = fst (runSetM act Set.empty)
+
+contains     :: Vertex -> SetM s Bool
+contains v    = SetM $ \ m -> (Set.member v m, m)
+
+include      :: Vertex -> SetM s ()
+include v     = SetM $ \ m -> ((), Set.insert v m)
+
+#endif /* !USE_ST_MONAD */
+
+-------------------------------------------------------------------------
+--                                                                      -
+--      Algorithms
+--                                                                      -
+-------------------------------------------------------------------------
+
+------------------------------------------------------------
+-- Algorithm 1: depth first search numbering
+------------------------------------------------------------
+
+preorder' :: Tree a -> [a] -> [a]
+preorder' (Node a ts) = (a :) . preorderF' ts
+
+preorderF' :: Forest a -> [a] -> [a]
+preorderF' ts = foldr (.) id $ map preorder' ts
+
+preorderF :: Forest a -> [a]
+preorderF ts = preorderF' ts []
+
+tabulate        :: Bounds -> [Vertex] -> Table Int
+tabulate bnds vs = array bnds (zipWith (,) vs [1..])
+
+preArr          :: Bounds -> Forest Vertex -> Table Int
+preArr bnds      = tabulate bnds . preorderF
+
+------------------------------------------------------------
+-- Algorithm 2: topological sorting
+------------------------------------------------------------
+
+postorder :: Tree a -> [a] -> [a]
+postorder (Node a ts) = postorderF ts . (a :)
+
+postorderF   :: Forest a -> [a] -> [a]
+postorderF ts = foldr (.) id $ map postorder ts
+
+postOrd :: Graph -> [Vertex]
+postOrd g = postorderF (dff g) []
+
+-- | A topological sort of the graph.
+-- The order is partially specified by the condition that a vertex /i/
+-- precedes /j/ whenever /j/ is reachable from /i/ but not vice versa.
+topSort      :: Graph -> [Vertex]
+topSort       = reverse . postOrd
+
+------------------------------------------------------------
+-- Algorithm 3: connected components
+------------------------------------------------------------
+
+-- | The connected components of a graph.
+-- Two vertices are connected if there is a path between them, traversing
+-- edges in either direction.
+components   :: Graph -> Forest Vertex
+components    = dff . undirected
+
+undirected   :: Graph -> Graph
+undirected g  = buildG (bounds g) (edges g ++ reverseE g)
+
+-- Algorithm 4: strongly connected components
+
+-- | The strongly connected components of a graph.
+scc  :: Graph -> Forest Vertex
+scc g = dfs g (reverse (postOrd (transposeG g)))
+
+------------------------------------------------------------
+-- Algorithm 5: Classifying edges
+------------------------------------------------------------
+
+{-
+XXX unused code
+
+tree              :: Bounds -> Forest Vertex -> Graph
+tree bnds ts       = buildG bnds (concat (map flat ts))
+ where flat (Node v ts') = [ (v, w) | Node w _us <- ts' ]
+                        ++ concat (map flat ts')
+
+back              :: Graph -> Table Int -> Graph
+back g post        = mapT select g
+ where select v ws = [ w | w <- ws, post!v < post!w ]
+
+cross             :: Graph -> Table Int -> Table Int -> Graph
+cross g pre post   = mapT select g
+ where select v ws = [ w | w <- ws, post!v > post!w, pre!v > pre!w ]
+
+forward           :: Graph -> Graph -> Table Int -> Graph
+forward g tree' pre = mapT select g
+ where select v ws = [ w | w <- ws, pre!v < pre!w ] \\ tree' ! v
+-}
+
+------------------------------------------------------------
+-- Algorithm 6: Finding reachable vertices
+------------------------------------------------------------
+
+-- | A list of vertices reachable from a given vertex.
+reachable    :: Graph -> Vertex -> [Vertex]
+reachable g v = preorderF (dfs g [v])
+
+-- | Is the second vertex reachable from the first?
+path         :: Graph -> Vertex -> Vertex -> Bool
+path g v w    = w `elem` (reachable g v)
+
+------------------------------------------------------------
+-- Algorithm 7: Biconnected components
+------------------------------------------------------------
+
+-- | The biconnected components of a graph.
+-- An undirected graph is biconnected if the deletion of any vertex
+-- leaves it connected.
+bcc :: Graph -> Forest [Vertex]
+bcc g = (concat . map bicomps . map (do_label g dnum)) forest
+ where forest = dff g
+       dnum   = preArr (bounds g) forest
+
+do_label :: Graph -> Table Int -> Tree Vertex -> Tree (Vertex,Int,Int)
+do_label g dnum (Node v ts) = Node (v,dnum!v,lv) us
+ where us = map (do_label g dnum) ts
+       lv = minimum ([dnum!v] ++ [dnum!w | w <- g!v]
+                     ++ [lu | Node (_,_,lu) _ <- us])
+
+bicomps :: Tree (Vertex,Int,Int) -> Forest [Vertex]
+bicomps (Node (v,_,_) ts)
+      = [ Node (v:vs) us | (_,Node vs us) <- map collect ts]
+
+collect :: Tree (Vertex,Int,Int) -> (Int, Tree [Vertex])
+collect (Node (v,dv,lv) ts) = (lv, Node (v:vs) cs)
+ where collected = map collect ts
+       vs = concat [ ws | (lw, Node ws _) <- collected, lw<dv]
+       cs = concat [ if lw<dv then us else [Node (v:ws) us]
+                        | (lw, Node ws us) <- collected ]
diff --git a/Data/IntMap.hs b/Data/IntMap.hs
new file mode 100644
--- /dev/null
+++ b/Data/IntMap.hs
@@ -0,0 +1,99 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.IntMap
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of maps from integer keys to values
+-- (dictionaries).
+--
+-- This module re-exports the value lazy "Data.IntMap.Lazy" API, plus
+-- several deprecated value strict functions. Please note that these functions
+-- have different strictness properties than those in "Data.IntMap.Strict":
+-- they only evaluate the result of the combining function. For example, the
+-- default value to 'insertWith'' is only evaluated if the combining function
+-- is called and uses it.
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.IntMap (IntMap)
+-- >  import qualified Data.IntMap as IntMap
+--
+-- The implementation is based on /big-endian patricia trees/.  This data
+-- structure performs especially well on binary operations like 'union'
+-- and 'intersection'.  However, my benchmarks show that it is also
+-- (much) faster on insertions and deletions when compared to a generic
+-- size-balanced map implementation (see "Data.Map").
+--
+--    * Chris Okasaki and Andy Gill,  \"/Fast Mergeable Integer Maps/\",
+--      Workshop on ML, September 1998, pages 77-86,
+--      <http://citeseer.ist.psu.edu/okasaki98fast.html>
+--
+--    * D.R. Morrison, \"/PATRICIA -- Practical Algorithm To Retrieve
+--      Information Coded In Alphanumeric/\", Journal of the ACM, 15(4),
+--      October 1968, pages 514-534.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation <http://en.wikipedia.org/wiki/Big_O_notation>.
+-- Many operations have a worst-case complexity of /O(min(n,W))/.
+-- This means that the operation can become linear in the number of
+-- elements with a maximum of /W/ -- the number of bits in an 'Int'
+-- (32 or 64).
+-----------------------------------------------------------------------------
+
+module Data.IntMap
+    ( module Data.IntMap.Lazy
+    , insertWith'
+    , insertWithKey'
+    , fold
+    , foldWithKey
+    ) where
+
+import Prelude ()  -- hide foldr
+import qualified Data.IntMap.Strict as Strict
+import Data.IntMap.Lazy
+
+-- | /Deprecated./ As of version 0.5, replaced by
+-- 'Data.IntMap.Strict.insertWith'.
+--
+-- /O(log n)/. Same as 'insertWith', but the result of the combining function
+-- is evaluated to WHNF before inserted to the map.
+
+insertWith' :: (a -> a -> a) -> Key -> a -> IntMap a -> IntMap a
+insertWith' = Strict.insertWith
+
+-- | /Deprecated./ As of version 0.5, replaced by
+-- 'Data.IntMap.Strict.insertWithKey'.
+--
+-- /O(log n)/. Same as 'insertWithKey', but the result of the combining
+-- function is evaluated to WHNF before inserted to the map.
+
+insertWithKey' :: (Key -> a -> a -> a) -> Key -> a -> IntMap a -> IntMap a
+insertWithKey' = Strict.insertWithKey
+
+-- | /Deprecated./ As of version 0.5, replaced by 'foldr'.
+--
+-- /O(n)/. Fold the values in the map using the given
+-- right-associative binary operator. This function is an equivalent
+-- of 'foldr' and is present for compatibility only.
+fold :: (a -> b -> b) -> b -> IntMap a -> b
+fold = foldr
+{-# INLINE fold #-}
+
+-- | /Deprecated./ As of version 0.5, replaced by 'foldrWithKey'.
+--
+-- /O(n)/. Fold the keys and values in the map using the given
+-- right-associative binary operator. This function is an equivalent
+-- of 'foldrWithKey' and is present for compatibility only.
+foldWithKey :: (Key -> a -> b -> b) -> b -> IntMap a -> b
+foldWithKey = foldrWithKey
+{-# INLINE foldWithKey #-}
diff --git a/Data/IntMap/Base.hs b/Data/IntMap/Base.hs
new file mode 100644
--- /dev/null
+++ b/Data/IntMap/Base.hs
@@ -0,0 +1,2197 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE MagicHash, DeriveDataTypeable, StandaloneDeriving #-}
+#endif
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+{-# LANGUAGE ScopedTypeVariables #-}
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE TypeFamilies #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.IntMap.Base
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- This defines the data structures and core (hidden) manipulations
+-- on representations.
+-----------------------------------------------------------------------------
+
+-- [Note: INLINE bit fiddling]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- It is essential that the bit fiddling functions like mask, zero, branchMask
+-- etc are inlined. If they do not, the memory allocation skyrockets. The GHC
+-- usually gets it right, but it is disastrous if it does not. Therefore we
+-- explicitly mark these functions INLINE.
+
+
+-- [Note: Local 'go' functions and capturing]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- Care must be taken when using 'go' function which captures an argument.
+-- Sometimes (for example when the argument is passed to a data constructor,
+-- as in insert), GHC heap-allocates more than necessary. Therefore C-- code
+-- must be checked for increased allocation when creating and modifying such
+-- functions.
+
+
+-- [Note: Order of constructors]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- The order of constructors of IntMap matters when considering performance.
+-- Currently in GHC 7.0, when type has 3 constructors, they are matched from
+-- the first to the last -- the best performance is achieved when the
+-- constructors are ordered by frequency.
+-- On GHC 7.0, reordering constructors from Nil | Tip | Bin to Bin | Tip | Nil
+-- improves the benchmark by circa 10%.
+
+module Data.IntMap.Base (
+    -- * Map type
+      IntMap(..), Key          -- instance Eq,Show
+
+    -- * Operators
+    , (!), (\\)
+
+    -- * Query
+    , null
+    , size
+    , member
+    , notMember
+    , lookup
+    , findWithDefault
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+
+    -- * Construction
+    , empty
+    , singleton
+
+    -- ** Insertion
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+
+    -- ** Delete\/Update
+    , delete
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+
+    -- * Combine
+
+    -- ** Union
+    , union
+    , unionWith
+    , unionWithKey
+    , unions
+    , unionsWith
+
+    -- ** Difference
+    , difference
+    , differenceWith
+    , differenceWithKey
+
+    -- ** Intersection
+    , intersection
+    , intersectionWith
+    , intersectionWithKey
+
+    -- ** Universal combining function
+    , mergeWithKey
+    , mergeWithKey'
+
+    -- * Traversal
+    -- ** Map
+    , map
+    , mapWithKey
+    , traverseWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeys
+    , mapKeysWith
+    , mapKeysMonotonic
+
+    -- * Folds
+    , foldr
+    , foldl
+    , foldrWithKey
+    , foldlWithKey
+    , foldMapWithKey
+
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    , foldrWithKey'
+    , foldlWithKey'
+
+    -- * Conversion
+    , elems
+    , keys
+    , assocs
+    , keysSet
+    , fromSet
+
+    -- ** Lists
+    , toList
+    , fromList
+    , fromListWith
+    , fromListWithKey
+
+    -- ** Ordered lists
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+
+    -- * Filter
+    , filter
+    , filterWithKey
+    , partition
+    , partitionWithKey
+
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+
+    , split
+    , splitLookup
+    , splitRoot
+
+    -- * Submap
+    , isSubmapOf, isSubmapOfBy
+    , isProperSubmapOf, isProperSubmapOfBy
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    , minView
+    , maxView
+    , minViewWithKey
+    , maxViewWithKey
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+
+    -- * Internal types
+    , Mask, Prefix, Nat
+
+    -- * Utility
+    , natFromInt
+    , intFromNat
+    , link
+    , bin
+    , zero
+    , nomatch
+    , match
+    , mask
+    , maskW
+    , shorter
+    , branchMask
+    , highestBitMask
+    , foldlStrict
+    ) where
+
+import Control.Applicative (Applicative(pure, (<*>)), (<$>))
+import Control.DeepSeq (NFData(rnf))
+import Control.Monad (liftM)
+import Data.Bits
+import qualified Data.Foldable as Foldable
+import Data.Maybe (fromMaybe)
+import Data.Monoid (Monoid(..))
+import Data.Traversable (Traversable(traverse))
+import Data.Typeable
+import Data.Word (Word)
+import Prelude hiding (lookup, map, filter, foldr, foldl, null)
+
+import Data.BitUtil
+import Data.IntSet.Base (Key)
+import qualified Data.IntSet.Base as IntSet
+import Data.StrictPair
+
+#if __GLASGOW_HASKELL__
+import Data.Data (Data(..), Constr, mkConstr, constrIndex, Fixity(Prefix),
+                  DataType, mkDataType)
+import GHC.Exts (build)
+#if __GLASGOW_HASKELL__ >= 708
+import qualified GHC.Exts as GHCExts
+#endif
+import Text.Read
+#endif
+
+-- Use macros to define strictness of functions.
+-- STRICT_x_OF_y denotes an y-ary function strict in the x-th parameter.
+-- We do not use BangPatterns, because they are not in any standard and we
+-- want the compilers to be compiled by as many compilers as possible.
+#define STRICT_1_OF_2(fn) fn arg _ | arg `seq` False = undefined
+
+-- A "Nat" is a natural machine word (an unsigned Int)
+type Nat = Word
+
+natFromInt :: Key -> Nat
+natFromInt = fromIntegral
+{-# INLINE natFromInt #-}
+
+intFromNat :: Nat -> Key
+intFromNat = fromIntegral
+{-# INLINE intFromNat #-}
+
+{--------------------------------------------------------------------
+  Types
+--------------------------------------------------------------------}
+
+
+-- | A map of integers to values @a@.
+
+-- See Note: Order of constructors
+data IntMap a = Bin {-# UNPACK #-} !Prefix
+                    {-# UNPACK #-} !Mask
+                    !(IntMap a)
+                    !(IntMap a)
+              | Tip {-# UNPACK #-} !Key a
+              | Nil
+
+type Prefix = Int
+type Mask   = Int
+
+{--------------------------------------------------------------------
+  Operators
+--------------------------------------------------------------------}
+
+-- | /O(min(n,W))/. Find the value at a key.
+-- Calls 'error' when the element can not be found.
+--
+-- > fromList [(5,'a'), (3,'b')] ! 1    Error: element not in the map
+-- > fromList [(5,'a'), (3,'b')] ! 5 == 'a'
+
+(!) :: IntMap a -> Key -> a
+m ! k = find k m
+
+-- | Same as 'difference'.
+(\\) :: IntMap a -> IntMap b -> IntMap a
+m1 \\ m2 = difference m1 m2
+
+infixl 9 \\{-This comment teaches CPP correct behaviour -}
+
+{--------------------------------------------------------------------
+  Types
+--------------------------------------------------------------------}
+
+instance Monoid (IntMap a) where
+    mempty  = empty
+    mappend = union
+    mconcat = unions
+
+instance Foldable.Foldable IntMap where
+  fold t = go t
+    where go Nil = mempty
+          go (Tip _ v) = v
+          go (Bin _ _ l r) = go l `mappend` go r
+  {-# INLINABLE fold #-}
+  foldr = foldr
+  {-# INLINE foldr #-}
+  foldl = foldl
+  {-# INLINE foldl #-}
+  foldMap f t = go t
+    where go Nil = mempty
+          go (Tip _ v) = f v
+          go (Bin _ _ l r) = go l `mappend` go r
+  {-# INLINE foldMap #-}
+
+instance Traversable IntMap where
+    traverse f = traverseWithKey (\_ -> f)
+    {-# INLINE traverse #-}
+
+instance NFData a => NFData (IntMap a) where
+    rnf Nil = ()
+    rnf (Tip _ v) = rnf v
+    rnf (Bin _ _ l r) = rnf l `seq` rnf r
+
+#if __GLASGOW_HASKELL__
+
+{--------------------------------------------------------------------
+  A Data instance
+--------------------------------------------------------------------}
+
+-- This instance preserves data abstraction at the cost of inefficiency.
+-- We provide limited reflection services for the sake of data abstraction.
+
+instance Data a => Data (IntMap a) where
+  gfoldl f z im = z fromList `f` (toList im)
+  toConstr _     = fromListConstr
+  gunfold k z c  = case constrIndex c of
+    1 -> k (z fromList)
+    _ -> error "gunfold"
+  dataTypeOf _   = intMapDataType
+  dataCast1 f    = gcast1 f
+
+fromListConstr :: Constr
+fromListConstr = mkConstr intMapDataType "fromList" [] Prefix
+
+intMapDataType :: DataType
+intMapDataType = mkDataType "Data.IntMap.Base.IntMap" [fromListConstr]
+
+#endif
+
+{--------------------------------------------------------------------
+  Query
+--------------------------------------------------------------------}
+-- | /O(1)/. Is the map empty?
+--
+-- > Data.IntMap.null (empty)           == True
+-- > Data.IntMap.null (singleton 1 'a') == False
+
+null :: IntMap a -> Bool
+null Nil = True
+null _   = False
+{-# INLINE null #-}
+
+-- | /O(n)/. Number of elements in the map.
+--
+-- > size empty                                   == 0
+-- > size (singleton 1 'a')                       == 1
+-- > size (fromList([(1,'a'), (2,'c'), (3,'b')])) == 3
+size :: IntMap a -> Int
+size t
+  = case t of
+      Bin _ _ l r -> size l + size r
+      Tip _ _ -> 1
+      Nil     -> 0
+
+-- | /O(min(n,W))/. Is the key a member of the map?
+--
+-- > member 5 (fromList [(5,'a'), (3,'b')]) == True
+-- > member 1 (fromList [(5,'a'), (3,'b')]) == False
+
+-- See Note: Local 'go' functions and capturing]
+member :: Key -> IntMap a -> Bool
+member k = k `seq` go
+  where
+    go (Bin p m l r) | nomatch k p m = False
+                     | zero k m  = go l
+                     | otherwise = go r
+    go (Tip kx _) = k == kx
+    go Nil = False
+
+infix 4 `member`
+
+-- | /O(min(n,W))/. Is the key not a member of the map?
+--
+-- > notMember 5 (fromList [(5,'a'), (3,'b')]) == False
+-- > notMember 1 (fromList [(5,'a'), (3,'b')]) == True
+
+notMember :: Key -> IntMap a -> Bool
+notMember k m = not $ member k m
+
+infix 4 `notMember`
+
+-- | /O(min(n,W))/. Lookup the value at a key in the map. See also 'Data.Map.lookup'.
+
+-- See Note: Local 'go' functions and capturing]
+lookup :: Key -> IntMap a -> Maybe a
+lookup k = k `seq` go
+  where
+    go (Bin p m l r) | nomatch k p m = Nothing
+                     | zero k m  = go l
+                     | otherwise = go r
+    go (Tip kx x) | k == kx   = Just x
+                  | otherwise = Nothing
+    go Nil = Nothing
+
+
+-- See Note: Local 'go' functions and capturing]
+find :: Key -> IntMap a -> a
+find k = k `seq` go
+  where
+    go (Bin p m l r) | nomatch k p m = not_found
+                     | zero k m  = go l
+                     | otherwise = go r
+    go (Tip kx x) | k == kx   = x
+                  | otherwise = not_found
+    go Nil = not_found
+
+    not_found = error ("IntMap.!: key " ++ show k ++ " is not an element of the map")
+
+-- | /O(min(n,W))/. The expression @('findWithDefault' def k map)@
+-- returns the value at key @k@ or returns @def@ when the key is not an
+-- element of the map.
+--
+-- > findWithDefault 'x' 1 (fromList [(5,'a'), (3,'b')]) == 'x'
+-- > findWithDefault 'x' 5 (fromList [(5,'a'), (3,'b')]) == 'a'
+
+-- See Note: Local 'go' functions and capturing]
+findWithDefault :: a -> Key -> IntMap a -> a
+findWithDefault def k = k `seq` go
+  where
+    go (Bin p m l r) | nomatch k p m = def
+                     | zero k m  = go l
+                     | otherwise = go r
+    go (Tip kx x) | k == kx   = x
+                  | otherwise = def
+    go Nil = def
+
+-- | /O(log n)/. Find largest key smaller than the given one and return the
+-- corresponding (key, value) pair.
+--
+-- > lookupLT 3 (fromList [(3,'a'), (5,'b')]) == Nothing
+-- > lookupLT 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
+
+-- See Note: Local 'go' functions and capturing.
+lookupLT :: Key -> IntMap a -> Maybe (Key, a)
+lookupLT k t = k `seq` case t of
+    Bin _ m l r | m < 0 -> if k >= 0 then go r l else go Nil r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch k p m = if k < p then unsafeFindMax def else unsafeFindMax r
+                         | zero k m  = go def l
+                         | otherwise = go l r
+    go def (Tip ky y) | k <= ky   = unsafeFindMax def
+                      | otherwise = Just (ky, y)
+    go def Nil = unsafeFindMax def
+
+-- | /O(log n)/. Find smallest key greater than the given one and return the
+-- corresponding (key, value) pair.
+--
+-- > lookupGT 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
+-- > lookupGT 5 (fromList [(3,'a'), (5,'b')]) == Nothing
+
+-- See Note: Local 'go' functions and capturing.
+lookupGT :: Key -> IntMap a -> Maybe (Key, a)
+lookupGT k t = k `seq` case t of
+    Bin _ m l r | m < 0 -> if k >= 0 then go Nil l else go l r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch k p m = if k < p then unsafeFindMin l else unsafeFindMin def
+                         | zero k m  = go r l
+                         | otherwise = go def r
+    go def (Tip ky y) | k >= ky   = unsafeFindMin def
+                      | otherwise = Just (ky, y)
+    go def Nil = unsafeFindMin def
+
+-- | /O(log n)/. Find largest key smaller or equal to the given one and return
+-- the corresponding (key, value) pair.
+--
+-- > lookupLE 2 (fromList [(3,'a'), (5,'b')]) == Nothing
+-- > lookupLE 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
+-- > lookupLE 5 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
+
+-- See Note: Local 'go' functions and capturing.
+lookupLE :: Key -> IntMap a -> Maybe (Key, a)
+lookupLE k t = k `seq` case t of
+    Bin _ m l r | m < 0 -> if k >= 0 then go r l else go Nil r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch k p m = if k < p then unsafeFindMax def else unsafeFindMax r
+                         | zero k m  = go def l
+                         | otherwise = go l r
+    go def (Tip ky y) | k < ky    = unsafeFindMax def
+                      | otherwise = Just (ky, y)
+    go def Nil = unsafeFindMax def
+
+-- | /O(log n)/. Find smallest key greater or equal to the given one and return
+-- the corresponding (key, value) pair.
+--
+-- > lookupGE 3 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
+-- > lookupGE 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
+-- > lookupGE 6 (fromList [(3,'a'), (5,'b')]) == Nothing
+
+-- See Note: Local 'go' functions and capturing.
+lookupGE :: Key -> IntMap a -> Maybe (Key, a)
+lookupGE k t = k `seq` case t of
+    Bin _ m l r | m < 0 -> if k >= 0 then go Nil l else go l r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch k p m = if k < p then unsafeFindMin l else unsafeFindMin def
+                         | zero k m  = go r l
+                         | otherwise = go def r
+    go def (Tip ky y) | k > ky    = unsafeFindMin def
+                      | otherwise = Just (ky, y)
+    go def Nil = unsafeFindMin def
+
+
+-- Helper function for lookupGE and lookupGT. It assumes that if a Bin node is
+-- given, it has m > 0.
+unsafeFindMin :: IntMap a -> Maybe (Key, a)
+unsafeFindMin Nil = Nothing
+unsafeFindMin (Tip ky y) = Just (ky, y)
+unsafeFindMin (Bin _ _ l _) = unsafeFindMin l
+
+-- Helper function for lookupLE and lookupLT. It assumes that if a Bin node is
+-- given, it has m > 0.
+unsafeFindMax :: IntMap a -> Maybe (Key, a)
+unsafeFindMax Nil = Nothing
+unsafeFindMax (Tip ky y) = Just (ky, y)
+unsafeFindMax (Bin _ _ _ r) = unsafeFindMax r
+
+{--------------------------------------------------------------------
+  Construction
+--------------------------------------------------------------------}
+-- | /O(1)/. The empty map.
+--
+-- > empty      == fromList []
+-- > size empty == 0
+
+empty :: IntMap a
+empty
+  = Nil
+{-# INLINE empty #-}
+
+-- | /O(1)/. A map of one element.
+--
+-- > singleton 1 'a'        == fromList [(1, 'a')]
+-- > size (singleton 1 'a') == 1
+
+singleton :: Key -> a -> IntMap a
+singleton k x
+  = Tip k x
+{-# INLINE singleton #-}
+
+{--------------------------------------------------------------------
+  Insert
+--------------------------------------------------------------------}
+-- | /O(min(n,W))/. Insert a new key\/value pair in the map.
+-- If the key is already present in the map, the associated value is
+-- replaced with the supplied value, i.e. 'insert' is equivalent to
+-- @'insertWith' 'const'@.
+--
+-- > insert 5 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'x')]
+-- > insert 7 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+-- > insert 5 'x' empty                         == singleton 5 'x'
+
+insert :: Key -> a -> IntMap a -> IntMap a
+insert k x t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> link k (Tip k x) p t
+      | zero k m      -> Bin p m (insert k x l) r
+      | otherwise     -> Bin p m l (insert k x r)
+    Tip ky _
+      | k==ky         -> Tip k x
+      | otherwise     -> link k (Tip k x) ky t
+    Nil -> Tip k x
+
+-- right-biased insertion, used by 'union'
+-- | /O(min(n,W))/. Insert with a combining function.
+-- @'insertWith' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert @f new_value old_value@.
+--
+-- > insertWith (++) 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "xxxa")]
+-- > insertWith (++) 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWith (++) 5 "xxx" empty                         == singleton 5 "xxx"
+
+insertWith :: (a -> a -> a) -> Key -> a -> IntMap a -> IntMap a
+insertWith f k x t
+  = insertWithKey (\_ x' y' -> f x' y') k x t
+
+-- | /O(min(n,W))/. Insert with a combining function.
+-- @'insertWithKey' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert @f key new_value old_value@.
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:xxx|a")]
+-- > insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWithKey f 5 "xxx" empty                         == singleton 5 "xxx"
+
+insertWithKey :: (Key -> a -> a -> a) -> Key -> a -> IntMap a -> IntMap a
+insertWithKey f k x t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> link k (Tip k x) p t
+      | zero k m      -> Bin p m (insertWithKey f k x l) r
+      | otherwise     -> Bin p m l (insertWithKey f k x r)
+    Tip ky y
+      | k==ky         -> Tip k (f k x y)
+      | otherwise     -> link k (Tip k x) ky t
+    Nil -> Tip k x
+
+-- | /O(min(n,W))/. The expression (@'insertLookupWithKey' f k x map@)
+-- is a pair where the first element is equal to (@'lookup' k map@)
+-- and the second element equal to (@'insertWithKey' f k x map@).
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:xxx|a")])
+-- > insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "xxx")])
+-- > insertLookupWithKey f 5 "xxx" empty                         == (Nothing,  singleton 5 "xxx")
+--
+-- This is how to define @insertLookup@ using @insertLookupWithKey@:
+--
+-- > let insertLookup kx x t = insertLookupWithKey (\_ a _ -> a) kx x t
+-- > insertLookup 5 "x" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "x")])
+-- > insertLookup 7 "x" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "x")])
+
+insertLookupWithKey :: (Key -> a -> a -> a) -> Key -> a -> IntMap a -> (Maybe a, IntMap a)
+insertLookupWithKey f k x t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> (Nothing,link k (Tip k x) p t)
+      | zero k m      -> let (found,l') = insertLookupWithKey f k x l in (found,Bin p m l' r)
+      | otherwise     -> let (found,r') = insertLookupWithKey f k x r in (found,Bin p m l r')
+    Tip ky y
+      | k==ky         -> (Just y,Tip k (f k x y))
+      | otherwise     -> (Nothing,link k (Tip k x) ky t)
+    Nil -> (Nothing,Tip k x)
+
+
+{--------------------------------------------------------------------
+  Deletion
+--------------------------------------------------------------------}
+-- | /O(min(n,W))/. Delete a key and its value from the map. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > delete 5 (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > delete 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > delete 5 empty                         == empty
+
+delete :: Key -> IntMap a -> IntMap a
+delete k t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> t
+      | zero k m      -> bin p m (delete k l) r
+      | otherwise     -> bin p m l (delete k r)
+    Tip ky _
+      | k==ky         -> Nil
+      | otherwise     -> t
+    Nil -> Nil
+
+-- | /O(min(n,W))/. Adjust a value at a specific key. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjust ("new " ++) 7 empty                         == empty
+
+adjust ::  (a -> a) -> Key -> IntMap a -> IntMap a
+adjust f k m
+  = adjustWithKey (\_ x -> f x) k m
+
+-- | /O(min(n,W))/. Adjust a value at a specific key. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > let f key x = (show key) ++ ":new " ++ x
+-- > adjustWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > adjustWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjustWithKey f 7 empty                         == empty
+
+adjustWithKey ::  (Key -> a -> a) -> Key -> IntMap a -> IntMap a
+adjustWithKey f
+  = updateWithKey (\k' x -> Just (f k' x))
+
+-- | /O(min(n,W))/. The expression (@'update' f k map@) updates the value @x@
+-- at @k@ (if it is in the map). If (@f x@) is 'Nothing', the element is
+-- deleted. If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > update f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > update f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > update f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+update ::  (a -> Maybe a) -> Key -> IntMap a -> IntMap a
+update f
+  = updateWithKey (\_ x -> f x)
+
+-- | /O(min(n,W))/. The expression (@'update' f k map@) updates the value @x@
+-- at @k@ (if it is in the map). If (@f k x@) is 'Nothing', the element is
+-- deleted. If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > updateWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > updateWithKey f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateWithKey ::  (Key -> a -> Maybe a) -> Key -> IntMap a -> IntMap a
+updateWithKey f k t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> t
+      | zero k m      -> bin p m (updateWithKey f k l) r
+      | otherwise     -> bin p m l (updateWithKey f k r)
+    Tip ky y
+      | k==ky         -> case (f k y) of
+                           Just y' -> Tip ky y'
+                           Nothing -> Nil
+      | otherwise     -> t
+    Nil -> Nil
+
+-- | /O(min(n,W))/. Lookup and update.
+-- The function returns original value, if it is updated.
+-- This is different behavior than 'Data.Map.updateLookupWithKey'.
+-- Returns the original key value if the map entry is deleted.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateLookupWithKey f 5 (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:new a")])
+-- > updateLookupWithKey f 7 (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a")])
+-- > updateLookupWithKey f 3 (fromList [(5,"a"), (3,"b")]) == (Just "b", singleton 5 "a")
+
+updateLookupWithKey ::  (Key -> a -> Maybe a) -> Key -> IntMap a -> (Maybe a,IntMap a)
+updateLookupWithKey f k t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> (Nothing,t)
+      | zero k m      -> let (found,l') = updateLookupWithKey f k l in (found,bin p m l' r)
+      | otherwise     -> let (found,r') = updateLookupWithKey f k r in (found,bin p m l r')
+    Tip ky y
+      | k==ky         -> case (f k y) of
+                           Just y' -> (Just y,Tip ky y')
+                           Nothing -> (Just y,Nil)
+      | otherwise     -> (Nothing,t)
+    Nil -> (Nothing,Nil)
+
+
+
+-- | /O(min(n,W))/. The expression (@'alter' f k map@) alters the value @x@ at @k@, or absence thereof.
+-- 'alter' can be used to insert, delete, or update a value in an 'IntMap'.
+-- In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.
+alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
+alter f k t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> case f Nothing of
+                           Nothing -> t
+                           Just x -> link k (Tip k x) p t
+      | zero k m      -> bin p m (alter f k l) r
+      | otherwise     -> bin p m l (alter f k r)
+    Tip ky y
+      | k==ky         -> case f (Just y) of
+                           Just x -> Tip ky x
+                           Nothing -> Nil
+      | otherwise     -> case f Nothing of
+                           Just x -> link k (Tip k x) ky t
+                           Nothing -> Tip ky y
+    Nil               -> case f Nothing of
+                           Just x -> Tip k x
+                           Nothing -> Nil
+
+
+{--------------------------------------------------------------------
+  Union
+--------------------------------------------------------------------}
+-- | The union of a list of maps.
+--
+-- > unions [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+-- >     == fromList [(3, "b"), (5, "a"), (7, "C")]
+-- > unions [(fromList [(5, "A3"), (3, "B3")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "a"), (3, "b")])]
+-- >     == fromList [(3, "B3"), (5, "A3"), (7, "C")]
+
+unions :: [IntMap a] -> IntMap a
+unions xs
+  = foldlStrict union empty xs
+
+-- | The union of a list of maps, with a combining operation.
+--
+-- > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+-- >     == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
+
+unionsWith :: (a->a->a) -> [IntMap a] -> IntMap a
+unionsWith f ts
+  = foldlStrict (unionWith f) empty ts
+
+-- | /O(n+m)/. The (left-biased) union of two maps.
+-- It prefers the first map when duplicate keys are encountered,
+-- i.e. (@'union' == 'unionWith' 'const'@).
+--
+-- > union (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "a"), (7, "C")]
+
+union :: IntMap a -> IntMap a -> IntMap a
+union m1 m2
+  = mergeWithKey' Bin const id id m1 m2
+
+infixl 5 `union`
+
+-- | /O(n+m)/. The union with a combining function.
+--
+-- > unionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "aA"), (7, "C")]
+
+unionWith :: (a -> a -> a) -> IntMap a -> IntMap a -> IntMap a
+unionWith f m1 m2
+  = unionWithKey (\_ x y -> f x y) m1 m2
+
+-- | /O(n+m)/. The union with a combining function.
+--
+-- > let f key left_value right_value = (show key) ++ ":" ++ left_value ++ "|" ++ right_value
+-- > unionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "5:a|A"), (7, "C")]
+
+unionWithKey :: (Key -> a -> a -> a) -> IntMap a -> IntMap a -> IntMap a
+unionWithKey f m1 m2
+  = mergeWithKey' Bin (\(Tip k1 x1) (Tip _k2 x2) -> Tip k1 (f k1 x1 x2)) id id m1 m2
+
+{--------------------------------------------------------------------
+  Difference
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Difference between two maps (based on keys).
+--
+-- > difference (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 3 "b"
+
+difference :: IntMap a -> IntMap b -> IntMap a
+difference m1 m2
+  = mergeWithKey (\_ _ _ -> Nothing) id (const Nil) m1 m2
+
+-- | /O(n+m)/. Difference with a combining function.
+--
+-- > let f al ar = if al == "b" then Just (al ++ ":" ++ ar) else Nothing
+-- > differenceWith f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (7, "C")])
+-- >     == singleton 3 "b:B"
+
+differenceWith :: (a -> b -> Maybe a) -> IntMap a -> IntMap b -> IntMap a
+differenceWith f m1 m2
+  = differenceWithKey (\_ x y -> f x y) m1 m2
+
+-- | /O(n+m)/. Difference with a combining function. When two equal keys are
+-- encountered, the combining function is applied to the key and both values.
+-- If it returns 'Nothing', the element is discarded (proper set difference).
+-- If it returns (@'Just' y@), the element is updated with a new value @y@.
+--
+-- > let f k al ar = if al == "b" then Just ((show k) ++ ":" ++ al ++ "|" ++ ar) else Nothing
+-- > differenceWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (10, "C")])
+-- >     == singleton 3 "3:b|B"
+
+differenceWithKey :: (Key -> a -> b -> Maybe a) -> IntMap a -> IntMap b -> IntMap a
+differenceWithKey f m1 m2
+  = mergeWithKey f id (const Nil) m1 m2
+
+
+{--------------------------------------------------------------------
+  Intersection
+--------------------------------------------------------------------}
+-- | /O(n+m)/. The (left-biased) intersection of two maps (based on keys).
+--
+-- > intersection (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "a"
+
+intersection :: IntMap a -> IntMap b -> IntMap a
+intersection m1 m2
+  = mergeWithKey' bin const (const Nil) (const Nil) m1 m2
+
+infixl 5 `intersection`
+
+-- | /O(n+m)/. The intersection with a combining function.
+--
+-- > intersectionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "aA"
+
+intersectionWith :: (a -> b -> c) -> IntMap a -> IntMap b -> IntMap c
+intersectionWith f m1 m2
+  = intersectionWithKey (\_ x y -> f x y) m1 m2
+
+-- | /O(n+m)/. The intersection with a combining function.
+--
+-- > let f k al ar = (show k) ++ ":" ++ al ++ "|" ++ ar
+-- > intersectionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "5:a|A"
+
+intersectionWithKey :: (Key -> a -> b -> c) -> IntMap a -> IntMap b -> IntMap c
+intersectionWithKey f m1 m2
+  = mergeWithKey' bin (\(Tip k1 x1) (Tip _k2 x2) -> Tip k1 (f k1 x1 x2)) (const Nil) (const Nil) m1 m2
+
+{--------------------------------------------------------------------
+  MergeWithKey
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. A high-performance universal combining function. Using
+-- 'mergeWithKey', all combining functions can be defined without any loss of
+-- efficiency (with exception of 'union', 'difference' and 'intersection',
+-- where sharing of some nodes is lost with 'mergeWithKey').
+--
+-- Please make sure you know what is going on when using 'mergeWithKey',
+-- otherwise you can be surprised by unexpected code growth or even
+-- corruption of the data structure.
+--
+-- When 'mergeWithKey' is given three arguments, it is inlined to the call
+-- site. You should therefore use 'mergeWithKey' only to define your custom
+-- combining functions. For example, you could define 'unionWithKey',
+-- 'differenceWithKey' and 'intersectionWithKey' as
+--
+-- > myUnionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) id id m1 m2
+-- > myDifferenceWithKey f m1 m2 = mergeWithKey f id (const empty) m1 m2
+-- > myIntersectionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) (const empty) (const empty) m1 m2
+--
+-- When calling @'mergeWithKey' combine only1 only2@, a function combining two
+-- 'IntMap's is created, such that
+--
+-- * if a key is present in both maps, it is passed with both corresponding
+--   values to the @combine@ function. Depending on the result, the key is either
+--   present in the result with specified value, or is left out;
+--
+-- * a nonempty subtree present only in the first map is passed to @only1@ and
+--   the output is added to the result;
+--
+-- * a nonempty subtree present only in the second map is passed to @only2@ and
+--   the output is added to the result.
+--
+-- The @only1@ and @only2@ methods /must return a map with a subset (possibly empty) of the keys of the given map/.
+-- The values can be modified arbitrarily. Most common variants of @only1@ and
+-- @only2@ are 'id' and @'const' 'empty'@, but for example @'map' f@ or
+-- @'filterWithKey' f@ could be used for any @f@.
+
+mergeWithKey :: (Key -> a -> b -> Maybe c) -> (IntMap a -> IntMap c) -> (IntMap b -> IntMap c)
+             -> IntMap a -> IntMap b -> IntMap c
+mergeWithKey f g1 g2 = mergeWithKey' bin combine g1 g2
+  where -- We use the lambda form to avoid non-exhaustive pattern matches warning.
+        combine = \(Tip k1 x1) (Tip _k2 x2) -> case f k1 x1 x2 of Nothing -> Nil
+                                                                  Just x -> Tip k1 x
+        {-# INLINE combine #-}
+{-# INLINE mergeWithKey #-}
+
+-- Slightly more general version of mergeWithKey. It differs in the following:
+--
+-- * the combining function operates on maps instead of keys and values. The
+--   reason is to enable sharing in union, difference and intersection.
+--
+-- * mergeWithKey' is given an equivalent of bin. The reason is that in union*,
+--   Bin constructor can be used, because we know both subtrees are nonempty.
+
+mergeWithKey' :: (Prefix -> Mask -> IntMap c -> IntMap c -> IntMap c)
+              -> (IntMap a -> IntMap b -> IntMap c) -> (IntMap a -> IntMap c) -> (IntMap b -> IntMap c)
+              -> IntMap a -> IntMap b -> IntMap c
+mergeWithKey' bin' f g1 g2 = go
+  where
+    go t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
+      | shorter m1 m2  = merge1
+      | shorter m2 m1  = merge2
+      | p1 == p2       = bin' p1 m1 (go l1 l2) (go r1 r2)
+      | otherwise      = maybe_link p1 (g1 t1) p2 (g2 t2)
+      where
+        merge1 | nomatch p2 p1 m1  = maybe_link p1 (g1 t1) p2 (g2 t2)
+               | zero p2 m1        = bin' p1 m1 (go l1 t2) (g1 r1)
+               | otherwise         = bin' p1 m1 (g1 l1) (go r1 t2)
+        merge2 | nomatch p1 p2 m2  = maybe_link p1 (g1 t1) p2 (g2 t2)
+               | zero p1 m2        = bin' p2 m2 (go t1 l2) (g2 r2)
+               | otherwise         = bin' p2 m2 (g2 l2) (go t1 r2)
+
+    go t1'@(Bin _ _ _ _) t2'@(Tip k2' _) = merge t2' k2' t1'
+      where merge t2 k2 t1@(Bin p1 m1 l1 r1) | nomatch k2 p1 m1 = maybe_link p1 (g1 t1) k2 (g2 t2)
+                                             | zero k2 m1 = bin' p1 m1 (merge t2 k2 l1) (g1 r1)
+                                             | otherwise  = bin' p1 m1 (g1 l1) (merge t2 k2 r1)
+            merge t2 k2 t1@(Tip k1 _) | k1 == k2 = f t1 t2
+                                      | otherwise = maybe_link k1 (g1 t1) k2 (g2 t2)
+            merge t2 _  Nil = g2 t2
+
+    go t1@(Bin _ _ _ _) Nil = g1 t1
+
+    go t1'@(Tip k1' _) t2' = merge t1' k1' t2'
+      where merge t1 k1 t2@(Bin p2 m2 l2 r2) | nomatch k1 p2 m2 = maybe_link k1 (g1 t1) p2 (g2 t2)
+                                             | zero k1 m2 = bin' p2 m2 (merge t1 k1 l2) (g2 r2)
+                                             | otherwise  = bin' p2 m2 (g2 l2) (merge t1 k1 r2)
+            merge t1 k1 t2@(Tip k2 _) | k1 == k2 = f t1 t2
+                                      | otherwise = maybe_link k1 (g1 t1) k2 (g2 t2)
+            merge t1 _  Nil = g1 t1
+
+    go Nil t2 = g2 t2
+
+    maybe_link _ Nil _ t2 = t2
+    maybe_link _ t1 _ Nil = t1
+    maybe_link p1 t1 p2 t2 = link p1 t1 p2 t2
+    {-# INLINE maybe_link #-}
+{-# INLINE mergeWithKey' #-}
+
+{--------------------------------------------------------------------
+  Min\/Max
+--------------------------------------------------------------------}
+
+-- | /O(min(n,W))/. Update the value at the minimal key.
+--
+-- > updateMinWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"3:b"), (5,"a")]
+-- > updateMinWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMinWithKey :: (Key -> a -> Maybe a) -> IntMap a -> IntMap a
+updateMinWithKey f t =
+  case t of Bin p m l r | m < 0 -> bin p m l (go f r)
+            _ -> go f t
+  where
+    go f' (Bin p m l r) = bin p m (go f' l) r
+    go f' (Tip k y) = case f' k y of
+                        Just y' -> Tip k y'
+                        Nothing -> Nil
+    go _ Nil = error "updateMinWithKey Nil"
+
+-- | /O(min(n,W))/. Update the value at the maximal key.
+--
+-- > updateMaxWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"b"), (5,"5:a")]
+-- > updateMaxWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMaxWithKey :: (Key -> a -> Maybe a) -> IntMap a -> IntMap a
+updateMaxWithKey f t =
+  case t of Bin p m l r | m < 0 -> bin p m (go f l) r
+            _ -> go f t
+  where
+    go f' (Bin p m l r) = bin p m l (go f' r)
+    go f' (Tip k y) = case f' k y of
+                        Just y' -> Tip k y'
+                        Nothing -> Nil
+    go _ Nil = error "updateMaxWithKey Nil"
+
+-- | /O(min(n,W))/. Retrieves the maximal (key,value) pair of the map, and
+-- the map stripped of that element, or 'Nothing' if passed an empty map.
+--
+-- > maxViewWithKey (fromList [(5,"a"), (3,"b")]) == Just ((5,"a"), singleton 3 "b")
+-- > maxViewWithKey empty == Nothing
+
+maxViewWithKey :: IntMap a -> Maybe ((Key, a), IntMap a)
+maxViewWithKey t =
+  case t of Nil -> Nothing
+            Bin p m l r | m < 0 -> case go l of (result, l') -> Just (result, bin p m l' r)
+            _ -> Just (go t)
+  where
+    go (Bin p m l r) = case go r of (result, r') -> (result, bin p m l r')
+    go (Tip k y) = ((k, y), Nil)
+    go Nil = error "maxViewWithKey Nil"
+
+-- | /O(min(n,W))/. Retrieves the minimal (key,value) pair of the map, and
+-- the map stripped of that element, or 'Nothing' if passed an empty map.
+--
+-- > minViewWithKey (fromList [(5,"a"), (3,"b")]) == Just ((3,"b"), singleton 5 "a")
+-- > minViewWithKey empty == Nothing
+
+minViewWithKey :: IntMap a -> Maybe ((Key, a), IntMap a)
+minViewWithKey t =
+  case t of Nil -> Nothing
+            Bin p m l r | m < 0 -> case go r of (result, r') -> Just (result, bin p m l r')
+            _ -> Just (go t)
+  where
+    go (Bin p m l r) = case go l of (result, l') -> (result, bin p m l' r)
+    go (Tip k y) = ((k, y), Nil)
+    go Nil = error "minViewWithKey Nil"
+
+-- | /O(min(n,W))/. Update the value at the maximal key.
+--
+-- > updateMax (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "Xa")]
+-- > updateMax (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMax :: (a -> Maybe a) -> IntMap a -> IntMap a
+updateMax f = updateMaxWithKey (const f)
+
+-- | /O(min(n,W))/. Update the value at the minimal key.
+--
+-- > updateMin (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "Xb"), (5, "a")]
+-- > updateMin (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMin :: (a -> Maybe a) -> IntMap a -> IntMap a
+updateMin f = updateMinWithKey (const f)
+
+-- Similar to the Arrow instance.
+first :: (a -> c) -> (a, b) -> (c, b)
+first f (x,y) = (f x,y)
+
+-- | /O(min(n,W))/. Retrieves the maximal key of the map, and the map
+-- stripped of that element, or 'Nothing' if passed an empty map.
+maxView :: IntMap a -> Maybe (a, IntMap a)
+maxView t = liftM (first snd) (maxViewWithKey t)
+
+-- | /O(min(n,W))/. Retrieves the minimal key of the map, and the map
+-- stripped of that element, or 'Nothing' if passed an empty map.
+minView :: IntMap a -> Maybe (a, IntMap a)
+minView t = liftM (first snd) (minViewWithKey t)
+
+-- | /O(min(n,W))/. Delete and find the maximal element.
+deleteFindMax :: IntMap a -> ((Key, a), IntMap a)
+deleteFindMax = fromMaybe (error "deleteFindMax: empty map has no maximal element") . maxViewWithKey
+
+-- | /O(min(n,W))/. Delete and find the minimal element.
+deleteFindMin :: IntMap a -> ((Key, a), IntMap a)
+deleteFindMin = fromMaybe (error "deleteFindMin: empty map has no minimal element") . minViewWithKey
+
+-- | /O(min(n,W))/. The minimal key of the map.
+findMin :: IntMap a -> (Key, a)
+findMin Nil = error $ "findMin: empty map has no minimal element"
+findMin (Tip k v) = (k,v)
+findMin (Bin _ m l r)
+  |   m < 0   = go r
+  | otherwise = go l
+    where go (Tip k v)      = (k,v)
+          go (Bin _ _ l' _) = go l'
+          go Nil            = error "findMax Nil"
+
+-- | /O(min(n,W))/. The maximal key of the map.
+findMax :: IntMap a -> (Key, a)
+findMax Nil = error $ "findMax: empty map has no maximal element"
+findMax (Tip k v) = (k,v)
+findMax (Bin _ m l r)
+  |   m < 0   = go l
+  | otherwise = go r
+    where go (Tip k v)      = (k,v)
+          go (Bin _ _ _ r') = go r'
+          go Nil            = error "findMax Nil"
+
+-- | /O(min(n,W))/. Delete the minimal key. Returns an empty map if the map is empty.
+--
+-- Note that this is a change of behaviour for consistency with 'Data.Map.Map' &#8211;
+-- versions prior to 0.5 threw an error if the 'IntMap' was already empty.
+deleteMin :: IntMap a -> IntMap a
+deleteMin = maybe Nil snd . minView
+
+-- | /O(min(n,W))/. Delete the maximal key. Returns an empty map if the map is empty.
+--
+-- Note that this is a change of behaviour for consistency with 'Data.Map.Map' &#8211;
+-- versions prior to 0.5 threw an error if the 'IntMap' was already empty.
+deleteMax :: IntMap a -> IntMap a
+deleteMax = maybe Nil snd . maxView
+
+
+{--------------------------------------------------------------------
+  Submap
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Is this a proper submap? (ie. a submap but not equal).
+-- Defined as (@'isProperSubmapOf' = 'isProperSubmapOfBy' (==)@).
+isProperSubmapOf :: Eq a => IntMap a -> IntMap a -> Bool
+isProperSubmapOf m1 m2
+  = isProperSubmapOfBy (==) m1 m2
+
+{- | /O(n+m)/. Is this a proper submap? (ie. a submap but not equal).
+ The expression (@'isProperSubmapOfBy' f m1 m2@) returns 'True' when
+ @m1@ and @m2@ are not equal,
+ all keys in @m1@ are in @m2@, and when @f@ returns 'True' when
+ applied to their respective values. For example, the following
+ expressions are all 'True':
+
+  > isProperSubmapOfBy (==) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+  > isProperSubmapOfBy (<=) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+
+ But the following are all 'False':
+
+  > isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)])
+  > isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1)])
+  > isProperSubmapOfBy (<)  (fromList [(1,1)])       (fromList [(1,1),(2,2)])
+-}
+isProperSubmapOfBy :: (a -> b -> Bool) -> IntMap a -> IntMap b -> Bool
+isProperSubmapOfBy predicate t1 t2
+  = case submapCmp predicate t1 t2 of
+      LT -> True
+      _  -> False
+
+submapCmp :: (a -> b -> Bool) -> IntMap a -> IntMap b -> Ordering
+submapCmp predicate t1@(Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  | shorter m1 m2  = GT
+  | shorter m2 m1  = submapCmpLt
+  | p1 == p2       = submapCmpEq
+  | otherwise      = GT  -- disjoint
+  where
+    submapCmpLt | nomatch p1 p2 m2  = GT
+                | zero p1 m2        = submapCmp predicate t1 l2
+                | otherwise         = submapCmp predicate t1 r2
+    submapCmpEq = case (submapCmp predicate l1 l2, submapCmp predicate r1 r2) of
+                    (GT,_ ) -> GT
+                    (_ ,GT) -> GT
+                    (EQ,EQ) -> EQ
+                    _       -> LT
+
+submapCmp _         (Bin _ _ _ _) _  = GT
+submapCmp predicate (Tip kx x) (Tip ky y)
+  | (kx == ky) && predicate x y = EQ
+  | otherwise                   = GT  -- disjoint
+submapCmp predicate (Tip k x) t
+  = case lookup k t of
+     Just y | predicate x y -> LT
+     _                      -> GT -- disjoint
+submapCmp _    Nil Nil = EQ
+submapCmp _    Nil _   = LT
+
+-- | /O(n+m)/. Is this a submap?
+-- Defined as (@'isSubmapOf' = 'isSubmapOfBy' (==)@).
+isSubmapOf :: Eq a => IntMap a -> IntMap a -> Bool
+isSubmapOf m1 m2
+  = isSubmapOfBy (==) m1 m2
+
+{- | /O(n+m)/.
+ The expression (@'isSubmapOfBy' f m1 m2@) returns 'True' if
+ all keys in @m1@ are in @m2@, and when @f@ returns 'True' when
+ applied to their respective values. For example, the following
+ expressions are all 'True':
+
+  > isSubmapOfBy (==) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+  > isSubmapOfBy (<=) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+  > isSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)])
+
+ But the following are all 'False':
+
+  > isSubmapOfBy (==) (fromList [(1,2)]) (fromList [(1,1),(2,2)])
+  > isSubmapOfBy (<) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+  > isSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1)])
+-}
+isSubmapOfBy :: (a -> b -> Bool) -> IntMap a -> IntMap b -> Bool
+isSubmapOfBy predicate t1@(Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  | shorter m1 m2  = False
+  | shorter m2 m1  = match p1 p2 m2 && (if zero p1 m2 then isSubmapOfBy predicate t1 l2
+                                                      else isSubmapOfBy predicate t1 r2)
+  | otherwise      = (p1==p2) && isSubmapOfBy predicate l1 l2 && isSubmapOfBy predicate r1 r2
+isSubmapOfBy _         (Bin _ _ _ _) _ = False
+isSubmapOfBy predicate (Tip k x) t     = case lookup k t of
+                                         Just y  -> predicate x y
+                                         Nothing -> False
+isSubmapOfBy _         Nil _           = True
+
+{--------------------------------------------------------------------
+  Mapping
+--------------------------------------------------------------------}
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > map (++ "x") (fromList [(5,"a"), (3,"b")]) == fromList [(3, "bx"), (5, "ax")]
+
+map :: (a -> b) -> IntMap a -> IntMap b
+map f t
+  = case t of
+      Bin p m l r -> Bin p m (map f l) (map f r)
+      Tip k x     -> Tip k (f x)
+      Nil         -> Nil
+
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > let f key x = (show key) ++ ":" ++ x
+-- > mapWithKey f (fromList [(5,"a"), (3,"b")]) == fromList [(3, "3:b"), (5, "5:a")]
+
+mapWithKey :: (Key -> a -> b) -> IntMap a -> IntMap b
+mapWithKey f t
+  = case t of
+      Bin p m l r -> Bin p m (mapWithKey f l) (mapWithKey f r)
+      Tip k x     -> Tip k (f k x)
+      Nil         -> Nil
+
+-- | /O(n)/.
+-- @'traverseWithKey' f s == 'fromList' <$> 'traverse' (\(k, v) -> (,) k <$> f k v) ('toList' m)@
+-- That is, behaves exactly like a regular 'traverse' except that the traversing
+-- function also has access to the key associated with a value.
+--
+-- > traverseWithKey (\k v -> if odd k then Just (succ v) else Nothing) (fromList [(1, 'a'), (5, 'e')]) == Just (fromList [(1, 'b'), (5, 'f')])
+-- > traverseWithKey (\k v -> if odd k then Just (succ v) else Nothing) (fromList [(2, 'c')])           == Nothing
+traverseWithKey :: Applicative t => (Key -> a -> t b) -> IntMap a -> t (IntMap b)
+traverseWithKey f = go
+  where
+    go Nil = pure Nil
+    go (Tip k v) = Tip k <$> f k v
+    go (Bin p m l r) = Bin p m <$> go l <*> go r
+{-# INLINE traverseWithKey #-}
+
+-- | /O(n)/. The function @'mapAccum'@ threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a b = (a ++ b, b ++ "X")
+-- > mapAccum f "Everything: " (fromList [(5,"a"), (3,"b")]) == ("Everything: ba", fromList [(3, "bX"), (5, "aX")])
+
+mapAccum :: (a -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccum f = mapAccumWithKey (\a' _ x -> f a' x)
+
+-- | /O(n)/. The function @'mapAccumWithKey'@ threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+-- > mapAccumWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) == ("Everything: 3-b 5-a", fromList [(3, "bX"), (5, "aX")])
+
+mapAccumWithKey :: (a -> Key -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccumWithKey f a t
+  = mapAccumL f a t
+
+-- | /O(n)/. The function @'mapAccumL'@ threads an accumulating
+-- argument through the map in ascending order of keys.
+mapAccumL :: (a -> Key -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccumL f a t
+  = case t of
+      Bin p m l r -> let (a1,l') = mapAccumL f a l
+                         (a2,r') = mapAccumL f a1 r
+                     in (a2,Bin p m l' r')
+      Tip k x     -> let (a',x') = f a k x in (a',Tip k x')
+      Nil         -> (a,Nil)
+
+-- | /O(n)/. The function @'mapAccumR'@ threads an accumulating
+-- argument through the map in descending order of keys.
+mapAccumRWithKey :: (a -> Key -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccumRWithKey f a t
+  = case t of
+      Bin p m l r -> let (a1,r') = mapAccumRWithKey f a r
+                         (a2,l') = mapAccumRWithKey f a1 l
+                     in (a2,Bin p m l' r')
+      Tip k x     -> let (a',x') = f a k x in (a',Tip k x')
+      Nil         -> (a,Nil)
+
+-- | /O(n*min(n,W))/.
+-- @'mapKeys' f s@ is the map obtained by applying @f@ to each key of @s@.
+--
+-- The size of the result may be smaller if @f@ maps two or more distinct
+-- keys to the same new key.  In this case the value at the greatest of the
+-- original keys is retained.
+--
+-- > mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])                        == fromList [(4, "b"), (6, "a")]
+-- > mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "c"
+-- > mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "c"
+
+mapKeys :: (Key->Key) -> IntMap a -> IntMap a
+mapKeys f = fromList . foldrWithKey (\k x xs -> (f k, x) : xs) []
+
+-- | /O(n*min(n,W))/.
+-- @'mapKeysWith' c f s@ is the map obtained by applying @f@ to each key of @s@.
+--
+-- The size of the result may be smaller if @f@ maps two or more distinct
+-- keys to the same new key.  In this case the associated values will be
+-- combined using @c@.
+--
+-- > mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "cdab"
+-- > mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "cdab"
+
+mapKeysWith :: (a -> a -> a) -> (Key->Key) -> IntMap a -> IntMap a
+mapKeysWith c f = fromListWith c . foldrWithKey (\k x xs -> (f k, x) : xs) []
+
+-- | /O(n*min(n,W))/.
+-- @'mapKeysMonotonic' f s == 'mapKeys' f s@, but works only when @f@
+-- is strictly monotonic.
+-- That is, for any values @x@ and @y@, if @x@ < @y@ then @f x@ < @f y@.
+-- /The precondition is not checked./
+-- Semi-formally, we have:
+--
+-- > and [x < y ==> f x < f y | x <- ls, y <- ls]
+-- >                     ==> mapKeysMonotonic f s == mapKeys f s
+-- >     where ls = keys s
+--
+-- This means that @f@ maps distinct original keys to distinct resulting keys.
+-- This function has slightly better performance than 'mapKeys'.
+--
+-- > mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")]) == fromList [(6, "b"), (10, "a")]
+
+mapKeysMonotonic :: (Key->Key) -> IntMap a -> IntMap a
+mapKeysMonotonic f = fromDistinctAscList . foldrWithKey (\k x xs -> (f k, x) : xs) []
+
+{--------------------------------------------------------------------
+  Filter
+--------------------------------------------------------------------}
+-- | /O(n)/. Filter all values that satisfy some predicate.
+--
+-- > filter (> "a") (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > filter (> "x") (fromList [(5,"a"), (3,"b")]) == empty
+-- > filter (< "a") (fromList [(5,"a"), (3,"b")]) == empty
+
+filter :: (a -> Bool) -> IntMap a -> IntMap a
+filter p m
+  = filterWithKey (\_ x -> p x) m
+
+-- | /O(n)/. Filter all keys\/values that satisfy some predicate.
+--
+-- > filterWithKey (\k _ -> k > 4) (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+filterWithKey :: (Key -> a -> Bool) -> IntMap a -> IntMap a
+filterWithKey predicate t
+  = case t of
+      Bin p m l r
+        -> bin p m (filterWithKey predicate l) (filterWithKey predicate r)
+      Tip k x
+        | predicate k x -> t
+        | otherwise     -> Nil
+      Nil -> Nil
+
+-- | /O(n)/. Partition the map according to some predicate. The first
+-- map contains all elements that satisfy the predicate, the second all
+-- elements that fail the predicate. See also 'split'.
+--
+-- > partition (> "a") (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", singleton 5 "a")
+-- > partition (< "x") (fromList [(5,"a"), (3,"b")]) == (fromList [(3, "b"), (5, "a")], empty)
+-- > partition (> "x") (fromList [(5,"a"), (3,"b")]) == (empty, fromList [(3, "b"), (5, "a")])
+
+partition :: (a -> Bool) -> IntMap a -> (IntMap a,IntMap a)
+partition p m
+  = partitionWithKey (\_ x -> p x) m
+
+-- | /O(n)/. Partition the map according to some predicate. The first
+-- map contains all elements that satisfy the predicate, the second all
+-- elements that fail the predicate. See also 'split'.
+--
+-- > partitionWithKey (\ k _ -> k > 3) (fromList [(5,"a"), (3,"b")]) == (singleton 5 "a", singleton 3 "b")
+-- > partitionWithKey (\ k _ -> k < 7) (fromList [(5,"a"), (3,"b")]) == (fromList [(3, "b"), (5, "a")], empty)
+-- > partitionWithKey (\ k _ -> k > 7) (fromList [(5,"a"), (3,"b")]) == (empty, fromList [(3, "b"), (5, "a")])
+
+partitionWithKey :: (Key -> a -> Bool) -> IntMap a -> (IntMap a,IntMap a)
+partitionWithKey predicate0 t0 = toPair $ go predicate0 t0
+  where
+    go predicate t
+      = case t of
+          Bin p m l r
+            -> let (l1 :*: l2) = go predicate l
+                   (r1 :*: r2) = go predicate r
+               in bin p m l1 r1 :*: bin p m l2 r2
+          Tip k x
+            | predicate k x -> (t :*: Nil)
+            | otherwise     -> (Nil :*: t)
+          Nil -> (Nil :*: Nil)
+
+-- | /O(n)/. Map values and collect the 'Just' results.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > mapMaybe f (fromList [(5,"a"), (3,"b")]) == singleton 5 "new a"
+
+mapMaybe :: (a -> Maybe b) -> IntMap a -> IntMap b
+mapMaybe f = mapMaybeWithKey (\_ x -> f x)
+
+-- | /O(n)/. Map keys\/values and collect the 'Just' results.
+--
+-- > let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
+-- > mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
+
+mapMaybeWithKey :: (Key -> a -> Maybe b) -> IntMap a -> IntMap b
+mapMaybeWithKey f (Bin p m l r)
+  = bin p m (mapMaybeWithKey f l) (mapMaybeWithKey f r)
+mapMaybeWithKey f (Tip k x) = case f k x of
+  Just y  -> Tip k y
+  Nothing -> Nil
+mapMaybeWithKey _ Nil = Nil
+
+-- | /O(n)/. Map values and separate the 'Left' and 'Right' results.
+--
+-- > let f a = if a < "c" then Left a else Right a
+-- > mapEither f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(3,"b"), (5,"a")], fromList [(1,"x"), (7,"z")])
+-- >
+-- > mapEither (\ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+
+mapEither :: (a -> Either b c) -> IntMap a -> (IntMap b, IntMap c)
+mapEither f m
+  = mapEitherWithKey (\_ x -> f x) m
+
+-- | /O(n)/. Map keys\/values and separate the 'Left' and 'Right' results.
+--
+-- > let f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
+-- > mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])
+-- >
+-- > mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])
+
+mapEitherWithKey :: (Key -> a -> Either b c) -> IntMap a -> (IntMap b, IntMap c)
+mapEitherWithKey f0 t0 = toPair $ go f0 t0
+  where
+    go f (Bin p m l r)
+      = bin p m l1 r1 :*: bin p m l2 r2
+      where
+        (l1 :*: l2) = go f l
+        (r1 :*: r2) = go f r
+    go f (Tip k x) = case f k x of
+      Left y  -> (Tip k y :*: Nil)
+      Right z -> (Nil :*: Tip k z)
+    go _ Nil = (Nil :*: Nil)
+
+-- | /O(min(n,W))/. The expression (@'split' k map@) is a pair @(map1,map2)@
+-- where all keys in @map1@ are lower than @k@ and all keys in
+-- @map2@ larger than @k@. Any key equal to @k@ is found in neither @map1@ nor @map2@.
+--
+-- > split 2 (fromList [(5,"a"), (3,"b")]) == (empty, fromList [(3,"b"), (5,"a")])
+-- > split 3 (fromList [(5,"a"), (3,"b")]) == (empty, singleton 5 "a")
+-- > split 4 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", singleton 5 "a")
+-- > split 5 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", empty)
+-- > split 6 (fromList [(5,"a"), (3,"b")]) == (fromList [(3,"b"), (5,"a")], empty)
+
+split :: Key -> IntMap a -> (IntMap a, IntMap a)
+split k t =
+  case t of
+      Bin _ m l r
+          | m < 0 -> if k >= 0 -- handle negative numbers.
+                     then case go k l of (lt :*: gt) -> let lt' = union r lt 
+                                                        in lt' `seq` (lt', gt)
+                     else case go k r of (lt :*: gt) -> let gt' = union gt l
+                                                        in gt' `seq` (lt, gt')
+      _ -> case go k t of
+          (lt :*: gt) -> (lt, gt)
+  where
+    go k' t'@(Bin p m l r) | nomatch k' p m = if k' > p then t' :*: Nil else Nil :*: t'
+                           | zero k' m = case go k' l of (lt :*: gt) -> lt :*: union gt r
+                           | otherwise = case go k' r of (lt :*: gt) -> union l lt :*: gt
+    go k' t'@(Tip ky _) | k' > ky   = (t' :*: Nil)
+                        | k' < ky   = (Nil :*: t')
+                        | otherwise = (Nil :*: Nil)
+    go _ Nil = (Nil :*: Nil)
+
+-- | /O(min(n,W))/. Performs a 'split' but also returns whether the pivot
+-- key was found in the original map.
+--
+-- > splitLookup 2 (fromList [(5,"a"), (3,"b")]) == (empty, Nothing, fromList [(3,"b"), (5,"a")])
+-- > splitLookup 3 (fromList [(5,"a"), (3,"b")]) == (empty, Just "b", singleton 5 "a")
+-- > splitLookup 4 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", Nothing, singleton 5 "a")
+-- > splitLookup 5 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", Just "a", empty)
+-- > splitLookup 6 (fromList [(5,"a"), (3,"b")]) == (fromList [(3,"b"), (5,"a")], Nothing, empty)
+
+splitLookup :: Key -> IntMap a -> (IntMap a, Maybe a, IntMap a)
+splitLookup k t =
+  case t of
+      Bin _ m l r
+          | m < 0 -> if k >= 0 -- handle negative numbers.
+                     then case go k l of
+                         (lt, fnd, gt) -> let lt' = union r lt
+                                          in lt' `seq` (lt', fnd, gt)
+                     else case go k r of
+                         (lt, fnd, gt) -> let gt' = union gt l
+                                          in gt' `seq` (lt, fnd, gt')
+      _ -> go k t
+  where
+    go k' t'@(Bin p m l r)
+        | nomatch k' p m = if k' > p then (t', Nothing, Nil) else (Nil, Nothing, t')
+        | zero k' m      = case go k' l of
+            (lt, fnd, gt) -> let gt' = union gt r in gt' `seq` (lt, fnd, gt')
+        | otherwise      = case go k' r of
+            (lt, fnd, gt) -> let lt' = union l lt in lt' `seq` (lt', fnd, gt)
+    go k' t'@(Tip ky y) | k' > ky   = (t', Nothing, Nil)
+                        | k' < ky   = (Nil, Nothing, t')
+                        | otherwise = (Nil, Just y, Nil)
+    go _ Nil = (Nil, Nothing, Nil)
+
+{--------------------------------------------------------------------
+  Fold
+--------------------------------------------------------------------}
+-- | /O(n)/. Fold the values in the map using the given right-associative
+-- binary operator, such that @'foldr' f z == 'Prelude.foldr' f z . 'elems'@.
+--
+-- For example,
+--
+-- > elems map = foldr (:) [] map
+--
+-- > let f a len = len + (length a)
+-- > foldr f 0 (fromList [(5,"a"), (3,"bbb")]) == 4
+foldr :: (a -> b -> b) -> b -> IntMap a -> b
+foldr f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z l) r -- put negative numbers before
+                        | otherwise -> go (go z r) l
+            _ -> go z t
+  where
+    go z' Nil           = z'
+    go z' (Tip _ x)     = f x z'
+    go z' (Bin _ _ l r) = go (go z' r) l
+{-# INLINE foldr #-}
+
+-- | /O(n)/. A strict version of 'foldr'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldr' :: (a -> b -> b) -> b -> IntMap a -> b
+foldr' f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z l) r -- put negative numbers before
+                        | otherwise -> go (go z r) l
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip _ x)     = f x z'
+    go z' (Bin _ _ l r) = go (go z' r) l
+{-# INLINE foldr' #-}
+
+-- | /O(n)/. Fold the values in the map using the given left-associative
+-- binary operator, such that @'foldl' f z == 'Prelude.foldl' f z . 'elems'@.
+--
+-- For example,
+--
+-- > elems = reverse . foldl (flip (:)) []
+--
+-- > let f len a = len + (length a)
+-- > foldl f 0 (fromList [(5,"a"), (3,"bbb")]) == 4
+foldl :: (a -> b -> a) -> a -> IntMap b -> a
+foldl f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z r) l -- put negative numbers before
+                        | otherwise -> go (go z l) r
+            _ -> go z t
+  where
+    go z' Nil           = z'
+    go z' (Tip _ x)     = f z' x
+    go z' (Bin _ _ l r) = go (go z' l) r
+{-# INLINE foldl #-}
+
+-- | /O(n)/. A strict version of 'foldl'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldl' :: (a -> b -> a) -> a -> IntMap b -> a
+foldl' f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z r) l -- put negative numbers before
+                        | otherwise -> go (go z l) r
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip _ x)     = f z' x
+    go z' (Bin _ _ l r) = go (go z' l) r
+{-# INLINE foldl' #-}
+
+-- | /O(n)/. Fold the keys and values in the map using the given right-associative
+-- binary operator, such that
+-- @'foldrWithKey' f z == 'Prelude.foldr' ('uncurry' f) z . 'toAscList'@.
+--
+-- For example,
+--
+-- > keys map = foldrWithKey (\k x ks -> k:ks) [] map
+--
+-- > let f k a result = result ++ "(" ++ (show k) ++ ":" ++ a ++ ")"
+-- > foldrWithKey f "Map: " (fromList [(5,"a"), (3,"b")]) == "Map: (5:a)(3:b)"
+foldrWithKey :: (Key -> a -> b -> b) -> b -> IntMap a -> b
+foldrWithKey f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z l) r -- put negative numbers before
+                        | otherwise -> go (go z r) l
+            _ -> go z t
+  where
+    go z' Nil           = z'
+    go z' (Tip kx x)    = f kx x z'
+    go z' (Bin _ _ l r) = go (go z' r) l
+{-# INLINE foldrWithKey #-}
+
+-- | /O(n)/. A strict version of 'foldrWithKey'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldrWithKey' :: (Key -> a -> b -> b) -> b -> IntMap a -> b
+foldrWithKey' f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z l) r -- put negative numbers before
+                        | otherwise -> go (go z r) l
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip kx x)    = f kx x z'
+    go z' (Bin _ _ l r) = go (go z' r) l
+{-# INLINE foldrWithKey' #-}
+
+-- | /O(n)/. Fold the keys and values in the map using the given left-associative
+-- binary operator, such that
+-- @'foldlWithKey' f z == 'Prelude.foldl' (\\z' (kx, x) -> f z' kx x) z . 'toAscList'@.
+--
+-- For example,
+--
+-- > keys = reverse . foldlWithKey (\ks k x -> k:ks) []
+--
+-- > let f result k a = result ++ "(" ++ (show k) ++ ":" ++ a ++ ")"
+-- > foldlWithKey f "Map: " (fromList [(5,"a"), (3,"b")]) == "Map: (3:b)(5:a)"
+foldlWithKey :: (a -> Key -> b -> a) -> a -> IntMap b -> a
+foldlWithKey f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z r) l -- put negative numbers before
+                        | otherwise -> go (go z l) r
+            _ -> go z t
+  where
+    go z' Nil           = z'
+    go z' (Tip kx x)    = f z' kx x
+    go z' (Bin _ _ l r) = go (go z' l) r
+{-# INLINE foldlWithKey #-}
+
+-- | /O(n)/. A strict version of 'foldlWithKey'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldlWithKey' :: (a -> Key -> b -> a) -> a -> IntMap b -> a
+foldlWithKey' f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z r) l -- put negative numbers before
+                        | otherwise -> go (go z l) r
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip kx x)    = f z' kx x
+    go z' (Bin _ _ l r) = go (go z' l) r
+{-# INLINE foldlWithKey' #-}
+
+-- | /O(n)/. Fold the keys and values in the map using the given monoid, such that
+--
+-- @'foldMapWithKey' f = 'Prelude.fold' . 'mapWithKey' f@
+--
+-- This can be an asymptotically faster than 'foldrWithKey' or 'foldlWithKey' for some monoids.
+foldMapWithKey :: Monoid m => (Key -> a -> m) -> IntMap a -> m
+foldMapWithKey f = go
+  where
+    go Nil           = mempty
+    go (Tip kx x)    = f kx x
+    go (Bin _ _ l r) = go l `mappend` go r
+{-# INLINE foldMapWithKey #-}
+
+{--------------------------------------------------------------------
+  List variations
+--------------------------------------------------------------------}
+-- | /O(n)/.
+-- Return all elements of the map in the ascending order of their keys.
+-- Subject to list fusion.
+--
+-- > elems (fromList [(5,"a"), (3,"b")]) == ["b","a"]
+-- > elems empty == []
+
+elems :: IntMap a -> [a]
+elems = foldr (:) []
+
+-- | /O(n)/. Return all keys of the map in ascending order. Subject to list
+-- fusion.
+--
+-- > keys (fromList [(5,"a"), (3,"b")]) == [3,5]
+-- > keys empty == []
+
+keys  :: IntMap a -> [Key]
+keys = foldrWithKey (\k _ ks -> k : ks) []
+
+-- | /O(n)/. An alias for 'toAscList'. Returns all key\/value pairs in the
+-- map in ascending key order. Subject to list fusion.
+--
+-- > assocs (fromList [(5,"a"), (3,"b")]) == [(3,"b"), (5,"a")]
+-- > assocs empty == []
+
+assocs :: IntMap a -> [(Key,a)]
+assocs = toAscList
+
+-- | /O(n*min(n,W))/. The set of all keys of the map.
+--
+-- > keysSet (fromList [(5,"a"), (3,"b")]) == Data.IntSet.fromList [3,5]
+-- > keysSet empty == Data.IntSet.empty
+
+keysSet :: IntMap a -> IntSet.IntSet
+keysSet Nil = IntSet.Nil
+keysSet (Tip kx _) = IntSet.singleton kx
+keysSet (Bin p m l r)
+  | m .&. IntSet.suffixBitMask == 0 = IntSet.Bin p m (keysSet l) (keysSet r)
+  | otherwise = IntSet.Tip (p .&. IntSet.prefixBitMask) (computeBm (computeBm 0 l) r)
+  where STRICT_1_OF_2(computeBm)
+        computeBm acc (Bin _ _ l' r') = computeBm (computeBm acc l') r'
+        computeBm acc (Tip kx _) = acc .|. IntSet.bitmapOf kx
+        computeBm _   Nil = error "Data.IntSet.keysSet: Nil"
+
+-- | /O(n)/. Build a map from a set of keys and a function which for each key
+-- computes its value.
+--
+-- > fromSet (\k -> replicate k 'a') (Data.IntSet.fromList [3, 5]) == fromList [(5,"aaaaa"), (3,"aaa")]
+-- > fromSet undefined Data.IntSet.empty == empty
+
+fromSet :: (Key -> a) -> IntSet.IntSet -> IntMap a
+fromSet _ IntSet.Nil = Nil
+fromSet f (IntSet.Bin p m l r) = Bin p m (fromSet f l) (fromSet f r)
+fromSet f (IntSet.Tip kx bm) = buildTree f kx bm (IntSet.suffixBitMask + 1)
+  where -- This is slightly complicated, as we to convert the dense
+        -- representation of IntSet into tree representation of IntMap.
+        --
+        -- We are given a nonzero bit mask 'bmask' of 'bits' bits with prefix 'prefix'.
+        -- We split bmask into halves corresponding to left and right subtree.
+        -- If they are both nonempty, we create a Bin node, otherwise exactly
+        -- one of them is nonempty and we construct the IntMap from that half.
+        buildTree g prefix bmask bits = prefix `seq` bmask `seq` case bits of
+          0 -> Tip prefix (g prefix)
+          _ -> case intFromNat ((natFromInt bits) `shiftRL` 1) of
+                 bits2 | bmask .&. ((1 `shiftLL` bits2) - 1) == 0 ->
+                           buildTree g (prefix + bits2) (bmask `shiftRL` bits2) bits2
+                       | (bmask `shiftRL` bits2) .&. ((1 `shiftLL` bits2) - 1) == 0 ->
+                           buildTree g prefix bmask bits2
+                       | otherwise ->
+                           Bin prefix bits2 (buildTree g prefix bmask bits2) (buildTree g (prefix + bits2) (bmask `shiftRL` bits2) bits2)
+
+{--------------------------------------------------------------------
+  Lists
+--------------------------------------------------------------------}
+#if __GLASGOW_HASKELL__ >= 708
+instance GHCExts.IsList (IntMap a) where
+  type Item (IntMap a) = (Key,a)
+  fromList = fromList
+  toList   = toList
+#endif
+
+-- | /O(n)/. Convert the map to a list of key\/value pairs. Subject to list
+-- fusion.
+--
+-- > toList (fromList [(5,"a"), (3,"b")]) == [(3,"b"), (5,"a")]
+-- > toList empty == []
+
+toList :: IntMap a -> [(Key,a)]
+toList = toAscList
+
+-- | /O(n)/. Convert the map to a list of key\/value pairs where the
+-- keys are in ascending order. Subject to list fusion.
+--
+-- > toAscList (fromList [(5,"a"), (3,"b")]) == [(3,"b"), (5,"a")]
+
+toAscList :: IntMap a -> [(Key,a)]
+toAscList = foldrWithKey (\k x xs -> (k,x):xs) []
+
+-- | /O(n)/. Convert the map to a list of key\/value pairs where the keys
+-- are in descending order. Subject to list fusion.
+--
+-- > toDescList (fromList [(5,"a"), (3,"b")]) == [(5,"a"), (3,"b")]
+
+toDescList :: IntMap a -> [(Key,a)]
+toDescList = foldlWithKey (\xs k x -> (k,x):xs) []
+
+-- List fusion for the list generating functions.
+#if __GLASGOW_HASKELL__
+-- The foldrFB and foldlFB are fold{r,l}WithKey equivalents, used for list fusion.
+-- They are important to convert unfused methods back, see mapFB in prelude.
+foldrFB :: (Key -> a -> b -> b) -> b -> IntMap a -> b
+foldrFB = foldrWithKey
+{-# INLINE[0] foldrFB #-}
+foldlFB :: (a -> Key -> b -> a) -> a -> IntMap b -> a
+foldlFB = foldlWithKey
+{-# INLINE[0] foldlFB #-}
+
+-- Inline assocs and toList, so that we need to fuse only toAscList.
+{-# INLINE assocs #-}
+{-# INLINE toList #-}
+
+-- The fusion is enabled up to phase 2 included. If it does not succeed,
+-- convert in phase 1 the expanded elems,keys,to{Asc,Desc}List calls back to
+-- elems,keys,to{Asc,Desc}List.  In phase 0, we inline fold{lr}FB (which were
+-- used in a list fusion, otherwise it would go away in phase 1), and let compiler
+-- do whatever it wants with elems,keys,to{Asc,Desc}List -- it was forbidden to
+-- inline it before phase 0, otherwise the fusion rules would not fire at all.
+{-# NOINLINE[0] elems #-}
+{-# NOINLINE[0] keys #-}
+{-# NOINLINE[0] toAscList #-}
+{-# NOINLINE[0] toDescList #-}
+{-# RULES "IntMap.elems" [~1] forall m . elems m = build (\c n -> foldrFB (\_ x xs -> c x xs) n m) #-}
+{-# RULES "IntMap.elemsBack" [1] foldrFB (\_ x xs -> x : xs) [] = elems #-}
+{-# RULES "IntMap.keys" [~1] forall m . keys m = build (\c n -> foldrFB (\k _ xs -> c k xs) n m) #-}
+{-# RULES "IntMap.keysBack" [1] foldrFB (\k _ xs -> k : xs) [] = keys #-}
+{-# RULES "IntMap.toAscList" [~1] forall m . toAscList m = build (\c n -> foldrFB (\k x xs -> c (k,x) xs) n m) #-}
+{-# RULES "IntMap.toAscListBack" [1] foldrFB (\k x xs -> (k, x) : xs) [] = toAscList #-}
+{-# RULES "IntMap.toDescList" [~1] forall m . toDescList m = build (\c n -> foldlFB (\xs k x -> c (k,x) xs) n m) #-}
+{-# RULES "IntMap.toDescListBack" [1] foldlFB (\xs k x -> (k, x) : xs) [] = toDescList #-}
+#endif
+
+
+-- | /O(n*min(n,W))/. Create a map from a list of key\/value pairs.
+--
+-- > fromList [] == empty
+-- > fromList [(5,"a"), (3,"b"), (5, "c")] == fromList [(5,"c"), (3,"b")]
+-- > fromList [(5,"c"), (3,"b"), (5, "a")] == fromList [(5,"a"), (3,"b")]
+
+fromList :: [(Key,a)] -> IntMap a
+fromList xs
+  = foldlStrict ins empty xs
+  where
+    ins t (k,x)  = insert k x t
+
+-- | /O(n*min(n,W))/. Create a map from a list of key\/value pairs with a combining function. See also 'fromAscListWith'.
+--
+-- > fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"c")] == fromList [(3, "ab"), (5, "cba")]
+-- > fromListWith (++) [] == empty
+
+fromListWith :: (a -> a -> a) -> [(Key,a)] -> IntMap a
+fromListWith f xs
+  = fromListWithKey (\_ x y -> f x y) xs
+
+-- | /O(n*min(n,W))/. Build a map from a list of key\/value pairs with a combining function. See also fromAscListWithKey'.
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > fromListWithKey f [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"c")] == fromList [(3, "3:a|b"), (5, "5:c|5:b|a")]
+-- > fromListWithKey f [] == empty
+
+fromListWithKey :: (Key -> a -> a -> a) -> [(Key,a)] -> IntMap a
+fromListWithKey f xs
+  = foldlStrict ins empty xs
+  where
+    ins t (k,x) = insertWithKey f k x t
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order.
+--
+-- > fromAscList [(3,"b"), (5,"a")]          == fromList [(3, "b"), (5, "a")]
+-- > fromAscList [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "b")]
+
+fromAscList :: [(Key,a)] -> IntMap a
+fromAscList xs
+  = fromAscListWithKey (\_ x _ -> x) xs
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order, with a combining function on equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "ba")]
+
+fromAscListWith :: (a -> a -> a) -> [(Key,a)] -> IntMap a
+fromAscListWith f xs
+  = fromAscListWithKey (\_ x y -> f x y) xs
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order, with a combining function on equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "5:b|a")]
+
+fromAscListWithKey :: (Key -> a -> a -> a) -> [(Key,a)] -> IntMap a
+fromAscListWithKey _ []         = Nil
+fromAscListWithKey f (x0 : xs0) = fromDistinctAscList (combineEq x0 xs0)
+  where
+    -- [combineEq f xs] combines equal elements with function [f] in an ordered list [xs]
+    combineEq z [] = [z]
+    combineEq z@(kz,zz) (x@(kx,xx):xs)
+      | kx==kz    = let yy = f kx xx zz in combineEq (kx,yy) xs
+      | otherwise = z:combineEq x xs
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order and all distinct.
+-- /The precondition (input list is strictly ascending) is not checked./
+--
+-- > fromDistinctAscList [(3,"b"), (5,"a")] == fromList [(3, "b"), (5, "a")]
+
+fromDistinctAscList :: forall a. [(Key,a)] -> IntMap a
+fromDistinctAscList []         = Nil
+fromDistinctAscList (z0 : zs0) = work z0 zs0 Nada
+  where
+    work (kx,vx) []            stk = finish kx (Tip kx vx) stk
+    work (kx,vx) (z@(kz,_):zs) stk = reduce z zs (branchMask kx kz) kx (Tip kx vx) stk
+
+    reduce :: (Key,a) -> [(Key,a)] -> Mask -> Prefix -> IntMap a -> Stack a -> IntMap a
+    reduce z zs _ px tx Nada = work z zs (Push px tx Nada)
+    reduce z zs m px tx stk@(Push py ty stk') =
+        let mxy = branchMask px py
+            pxy = mask px mxy
+        in  if shorter m mxy
+                 then reduce z zs m pxy (Bin pxy mxy ty tx) stk'
+                 else work z zs (Push px tx stk)
+
+    finish _  t  Nada = t
+    finish px tx (Push py ty stk) = finish p (link py ty px tx) stk
+        where m = branchMask px py
+              p = mask px m
+
+data Stack a = Push {-# UNPACK #-} !Prefix !(IntMap a) !(Stack a) | Nada
+
+
+{--------------------------------------------------------------------
+  Eq
+--------------------------------------------------------------------}
+instance Eq a => Eq (IntMap a) where
+  t1 == t2  = equal t1 t2
+  t1 /= t2  = nequal t1 t2
+
+equal :: Eq a => IntMap a -> IntMap a -> Bool
+equal (Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  = (m1 == m2) && (p1 == p2) && (equal l1 l2) && (equal r1 r2)
+equal (Tip kx x) (Tip ky y)
+  = (kx == ky) && (x==y)
+equal Nil Nil = True
+equal _   _   = False
+
+nequal :: Eq a => IntMap a -> IntMap a -> Bool
+nequal (Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  = (m1 /= m2) || (p1 /= p2) || (nequal l1 l2) || (nequal r1 r2)
+nequal (Tip kx x) (Tip ky y)
+  = (kx /= ky) || (x/=y)
+nequal Nil Nil = False
+nequal _   _   = True
+
+{--------------------------------------------------------------------
+  Ord
+--------------------------------------------------------------------}
+
+instance Ord a => Ord (IntMap a) where
+    compare m1 m2 = compare (toList m1) (toList m2)
+
+{--------------------------------------------------------------------
+  Functor
+--------------------------------------------------------------------}
+
+instance Functor IntMap where
+    fmap = map
+
+{--------------------------------------------------------------------
+  Show
+--------------------------------------------------------------------}
+
+instance Show a => Show (IntMap a) where
+  showsPrec d m   = showParen (d > 10) $
+    showString "fromList " . shows (toList m)
+
+{--------------------------------------------------------------------
+  Read
+--------------------------------------------------------------------}
+instance (Read e) => Read (IntMap e) where
+#ifdef __GLASGOW_HASKELL__
+  readPrec = parens $ prec 10 $ do
+    Ident "fromList" <- lexP
+    xs <- readPrec
+    return (fromList xs)
+
+  readListPrec = readListPrecDefault
+#else
+  readsPrec p = readParen (p > 10) $ \ r -> do
+    ("fromList",s) <- lex r
+    (xs,t) <- reads s
+    return (fromList xs,t)
+#endif
+
+{--------------------------------------------------------------------
+  Typeable
+--------------------------------------------------------------------}
+
+#include "Typeable.h"
+INSTANCE_TYPEABLE1(IntMap,intMapTc,"IntMap")
+
+{--------------------------------------------------------------------
+  Helpers
+--------------------------------------------------------------------}
+{--------------------------------------------------------------------
+  Link
+--------------------------------------------------------------------}
+link :: Prefix -> IntMap a -> Prefix -> IntMap a -> IntMap a
+link p1 t1 p2 t2
+  | zero p1 m = Bin p m t1 t2
+  | otherwise = Bin p m t2 t1
+  where
+    m = branchMask p1 p2
+    p = mask p1 m
+{-# INLINE link #-}
+
+{--------------------------------------------------------------------
+  @bin@ assures that we never have empty trees within a tree.
+--------------------------------------------------------------------}
+bin :: Prefix -> Mask -> IntMap a -> IntMap a -> IntMap a
+bin _ _ l Nil = l
+bin _ _ Nil r = r
+bin p m l r   = Bin p m l r
+{-# INLINE bin #-}
+
+
+{--------------------------------------------------------------------
+  Endian independent bit twiddling
+--------------------------------------------------------------------}
+zero :: Key -> Mask -> Bool
+zero i m
+  = (natFromInt i) .&. (natFromInt m) == 0
+{-# INLINE zero #-}
+
+nomatch,match :: Key -> Prefix -> Mask -> Bool
+nomatch i p m
+  = (mask i m) /= p
+{-# INLINE nomatch #-}
+
+match i p m
+  = (mask i m) == p
+{-# INLINE match #-}
+
+mask :: Key -> Mask -> Prefix
+mask i m
+  = maskW (natFromInt i) (natFromInt m)
+{-# INLINE mask #-}
+
+
+{--------------------------------------------------------------------
+  Big endian operations
+--------------------------------------------------------------------}
+maskW :: Nat -> Nat -> Prefix
+maskW i m
+  = intFromNat (i .&. (complement (m-1) `xor` m))
+{-# INLINE maskW #-}
+
+shorter :: Mask -> Mask -> Bool
+shorter m1 m2
+  = (natFromInt m1) > (natFromInt m2)
+{-# INLINE shorter #-}
+
+branchMask :: Prefix -> Prefix -> Mask
+branchMask p1 p2
+  = intFromNat (highestBitMask (natFromInt p1 `xor` natFromInt p2))
+{-# INLINE branchMask #-}
+
+{--------------------------------------------------------------------
+  Utilities
+--------------------------------------------------------------------}
+
+foldlStrict :: (a -> b -> a) -> a -> [b] -> a
+foldlStrict f = go
+  where
+    go z []     = z
+    go z (x:xs) = let z' = f z x in z' `seq` go z' xs
+{-# INLINE foldlStrict #-}
+
+-- | /O(1)/.  Decompose a map into pieces based on the structure of the underlying
+-- tree.  This function is useful for consuming a map in parallel.
+--
+-- No guarantee is made as to the sizes of the pieces; an internal, but
+-- deterministic process determines this.  However, it is guaranteed that the
+-- pieces returned will be in ascending order (all elements in the first submap
+-- less than all elements in the second, and so on).
+--
+-- Examples:
+--
+-- > splitRoot (fromList (zip [1..6::Int] ['a'..])) ==
+-- >   [fromList [(1,'a'),(2,'b'),(3,'c')],fromList [(4,'d'),(5,'e'),(6,'f')]]
+--
+-- > splitRoot empty == []
+--
+--  Note that the current implementation does not return more than two submaps,
+--  but you should not depend on this behaviour because it can change in the
+--  future without notice.
+splitRoot :: IntMap a -> [IntMap a]
+splitRoot orig =
+  case orig of
+    Nil -> []
+    x@(Tip _ _) -> [x]
+    Bin _ m l r | m < 0 -> [r, l]
+                | otherwise -> [l, r]
+{-# INLINE splitRoot #-}
+
+
+{--------------------------------------------------------------------
+  Debugging
+--------------------------------------------------------------------}
+-- | /O(n)/. Show the tree that implements the map. The tree is shown
+-- in a compressed, hanging format.
+showTree :: Show a => IntMap a -> String
+showTree s
+  = showTreeWith True False s
+
+
+{- | /O(n)/. The expression (@'showTreeWith' hang wide map@) shows
+ the tree that implements the map. If @hang@ is
+ 'True', a /hanging/ tree is shown otherwise a rotated tree is shown. If
+ @wide@ is 'True', an extra wide version is shown.
+-}
+showTreeWith :: Show a => Bool -> Bool -> IntMap a -> String
+showTreeWith hang wide t
+  | hang      = (showsTreeHang wide [] t) ""
+  | otherwise = (showsTree wide [] [] t) ""
+
+showsTree :: Show a => Bool -> [String] -> [String] -> IntMap a -> ShowS
+showsTree wide lbars rbars t
+  = case t of
+      Bin p m l r
+          -> showsTree wide (withBar rbars) (withEmpty rbars) r .
+             showWide wide rbars .
+             showsBars lbars . showString (showBin p m) . showString "\n" .
+             showWide wide lbars .
+             showsTree wide (withEmpty lbars) (withBar lbars) l
+      Tip k x
+          -> showsBars lbars . showString " " . shows k . showString ":=" . shows x . showString "\n"
+      Nil -> showsBars lbars . showString "|\n"
+
+showsTreeHang :: Show a => Bool -> [String] -> IntMap a -> ShowS
+showsTreeHang wide bars t
+  = case t of
+      Bin p m l r
+          -> showsBars bars . showString (showBin p m) . showString "\n" .
+             showWide wide bars .
+             showsTreeHang wide (withBar bars) l .
+             showWide wide bars .
+             showsTreeHang wide (withEmpty bars) r
+      Tip k x
+          -> showsBars bars . showString " " . shows k . showString ":=" . shows x . showString "\n"
+      Nil -> showsBars bars . showString "|\n"
+
+showBin :: Prefix -> Mask -> String
+showBin _ _
+  = "*" -- ++ show (p,m)
+
+showWide :: Bool -> [String] -> String -> String
+showWide wide bars
+  | wide      = showString (concat (reverse bars)) . showString "|\n"
+  | otherwise = id
+
+showsBars :: [String] -> ShowS
+showsBars bars
+  = case bars of
+      [] -> id
+      _  -> showString (concat (reverse (tail bars))) . showString node
+
+node :: String
+node           = "+--"
+
+withBar, withEmpty :: [String] -> [String]
+withBar bars   = "|  ":bars
+withEmpty bars = "   ":bars
diff --git a/Data/IntMap/Lazy.hs b/Data/IntMap/Lazy.hs
new file mode 100644
--- /dev/null
+++ b/Data/IntMap/Lazy.hs
@@ -0,0 +1,217 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.IntMap.Lazy
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of maps from integer keys to values
+-- (dictionaries).
+--
+-- API of this module is strict in the keys, but lazy in the values.
+-- If you need value-strict maps, use "Data.IntMap.Strict" instead.
+-- The 'IntMap' type itself is shared between the lazy and strict modules,
+-- meaning that the same 'IntMap' value can be passed to functions in
+-- both modules (although that is rarely needed).
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.IntMap.Lazy (IntMap)
+-- >  import qualified Data.IntMap.Lazy as IntMap
+--
+-- The implementation is based on /big-endian patricia trees/.  This data
+-- structure performs especially well on binary operations like 'union'
+-- and 'intersection'.  However, my benchmarks show that it is also
+-- (much) faster on insertions and deletions when compared to a generic
+-- size-balanced map implementation (see "Data.Map").
+--
+--    * Chris Okasaki and Andy Gill,  \"/Fast Mergeable Integer Maps/\",
+--      Workshop on ML, September 1998, pages 77-86,
+--      <http://citeseer.ist.psu.edu/okasaki98fast.html>
+--
+--    * D.R. Morrison, \"/PATRICIA -- Practical Algorithm To Retrieve
+--      Information Coded In Alphanumeric/\", Journal of the ACM, 15(4),
+--      October 1968, pages 514-534.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation <http://en.wikipedia.org/wiki/Big_O_notation>.
+-- Many operations have a worst-case complexity of /O(min(n,W))/.
+-- This means that the operation can become linear in the number of
+-- elements with a maximum of /W/ -- the number of bits in an 'Int'
+-- (32 or 64).
+-----------------------------------------------------------------------------
+
+module Data.IntMap.Lazy (
+    -- * Strictness properties
+    -- $strictness
+
+    -- * Map type
+#if !defined(TESTING)
+    IntMap, Key          -- instance Eq,Show
+#else
+    IntMap(..), Key          -- instance Eq,Show
+#endif
+
+    -- * Operators
+    , (!), (\\)
+
+    -- * Query
+    , IM.null
+    , size
+    , member
+    , notMember
+    , IM.lookup
+    , findWithDefault
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+
+    -- * Construction
+    , empty
+    , singleton
+
+    -- ** Insertion
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+
+    -- ** Delete\/Update
+    , delete
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+
+    -- * Combine
+
+    -- ** Union
+    , union
+    , unionWith
+    , unionWithKey
+    , unions
+    , unionsWith
+
+    -- ** Difference
+    , difference
+    , differenceWith
+    , differenceWithKey
+
+    -- ** Intersection
+    , intersection
+    , intersectionWith
+    , intersectionWithKey
+
+    -- ** Universal combining function
+    , mergeWithKey
+
+    -- * Traversal
+    -- ** Map
+    , IM.map
+    , mapWithKey
+    , traverseWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeys
+    , mapKeysWith
+    , mapKeysMonotonic
+
+    -- * Folds
+    , IM.foldr
+    , IM.foldl
+    , foldrWithKey
+    , foldlWithKey
+    , foldMapWithKey
+
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    , foldrWithKey'
+    , foldlWithKey'
+
+    -- * Conversion
+    , elems
+    , keys
+    , assocs
+    , keysSet
+    , fromSet
+
+    -- ** Lists
+    , toList
+    , fromList
+    , fromListWith
+    , fromListWithKey
+
+    -- ** Ordered lists
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+
+    -- * Filter
+    , IM.filter
+    , filterWithKey
+    , partition
+    , partitionWithKey
+
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+
+    , split
+    , splitLookup
+    , splitRoot
+
+    -- * Submap
+    , isSubmapOf, isSubmapOfBy
+    , isProperSubmapOf, isProperSubmapOfBy
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    , minView
+    , maxView
+    , minViewWithKey
+    , maxViewWithKey
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+    ) where
+
+import Data.IntMap.Base as IM
+
+-- $strictness
+--
+-- This module satisfies the following strictness property:
+--
+-- * Key arguments are evaluated to WHNF
+--
+-- Here are some examples that illustrate the property:
+--
+-- > insertWith (\ new old -> old) undefined v m  ==  undefined
+-- > insertWith (\ new old -> old) k undefined m  ==  OK
+-- > delete undefined m  ==  undefined
diff --git a/Data/IntMap/Strict.hs b/Data/IntMap/Strict.hs
new file mode 100644
--- /dev/null
+++ b/Data/IntMap/Strict.hs
@@ -0,0 +1,978 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.IntMap.Strict
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of maps from integer keys to values
+-- (dictionaries).
+--
+-- API of this module is strict in both the keys and the values.
+-- If you need value-lazy maps, use "Data.IntMap.Lazy" instead.
+-- The 'IntMap' type itself is shared between the lazy and strict modules,
+-- meaning that the same 'IntMap' value can be passed to functions in
+-- both modules (although that is rarely needed).
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.IntMap.Strict (IntMap)
+-- >  import qualified Data.IntMap.Strict as IntMap
+--
+-- The implementation is based on /big-endian patricia trees/.  This data
+-- structure performs especially well on binary operations like 'union'
+-- and 'intersection'.  However, my benchmarks show that it is also
+-- (much) faster on insertions and deletions when compared to a generic
+-- size-balanced map implementation (see "Data.Map").
+--
+--    * Chris Okasaki and Andy Gill,  \"/Fast Mergeable Integer Maps/\",
+--      Workshop on ML, September 1998, pages 77-86,
+--      <http://citeseer.ist.psu.edu/okasaki98fast.html>
+--
+--    * D.R. Morrison, \"/PATRICIA -- Practical Algorithm To Retrieve
+--      Information Coded In Alphanumeric/\", Journal of the ACM, 15(4),
+--      October 1968, pages 514-534.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation <http://en.wikipedia.org/wiki/Big_O_notation>.
+-- Many operations have a worst-case complexity of /O(min(n,W))/.
+-- This means that the operation can become linear in the number of
+-- elements with a maximum of /W/ -- the number of bits in an 'Int'
+-- (32 or 64).
+--
+-- Be aware that the 'Functor', 'Traversable' and 'Data' instances
+-- are the same as for the "Data.IntMap.Lazy" module, so if they are used
+-- on strict maps, the resulting maps will be lazy.
+-----------------------------------------------------------------------------
+
+-- See the notes at the beginning of Data.IntMap.Base.
+
+module Data.IntMap.Strict (
+    -- * Strictness properties
+    -- $strictness
+
+    -- * Map type
+#if !defined(TESTING)
+    IntMap, Key          -- instance Eq,Show
+#else
+    IntMap(..), Key          -- instance Eq,Show
+#endif
+
+    -- * Operators
+    , (!), (\\)
+
+    -- * Query
+    , null
+    , size
+    , member
+    , notMember
+    , lookup
+    , findWithDefault
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+
+    -- * Construction
+    , empty
+    , singleton
+
+    -- ** Insertion
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+
+    -- ** Delete\/Update
+    , delete
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+
+    -- * Combine
+
+    -- ** Union
+    , union
+    , unionWith
+    , unionWithKey
+    , unions
+    , unionsWith
+
+    -- ** Difference
+    , difference
+    , differenceWith
+    , differenceWithKey
+
+    -- ** Intersection
+    , intersection
+    , intersectionWith
+    , intersectionWithKey
+
+    -- ** Universal combining function
+    , mergeWithKey
+
+    -- * Traversal
+    -- ** Map
+    , map
+    , mapWithKey
+    , traverseWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeys
+    , mapKeysWith
+    , mapKeysMonotonic
+
+    -- * Folds
+    , foldr
+    , foldl
+    , foldrWithKey
+    , foldlWithKey
+    , foldMapWithKey
+
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    , foldrWithKey'
+    , foldlWithKey'
+
+    -- * Conversion
+    , elems
+    , keys
+    , assocs
+    , keysSet
+    , fromSet
+
+    -- ** Lists
+    , toList
+    , fromList
+    , fromListWith
+    , fromListWithKey
+
+    -- ** Ordered lists
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+
+    -- * Filter
+    , filter
+    , filterWithKey
+    , partition
+    , partitionWithKey
+
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+
+    , split
+    , splitLookup
+    , splitRoot
+
+    -- * Submap
+    , isSubmapOf, isSubmapOfBy
+    , isProperSubmapOf, isProperSubmapOfBy
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    , minView
+    , maxView
+    , minViewWithKey
+    , maxViewWithKey
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+    ) where
+
+import Prelude hiding (lookup,map,filter,foldr,foldl,null)
+
+import Data.Bits
+import Data.IntMap.Base hiding
+    ( findWithDefault
+    , singleton
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+    , unionsWith
+    , unionWith
+    , unionWithKey
+    , differenceWith
+    , differenceWithKey
+    , intersectionWith
+    , intersectionWithKey
+    , mergeWithKey
+    , updateMinWithKey
+    , updateMaxWithKey
+    , updateMax
+    , updateMin
+    , map
+    , mapWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeysWith
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+    , fromSet
+    , fromList
+    , fromListWith
+    , fromListWithKey
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+    )
+
+import Data.BitUtil
+import qualified Data.IntSet.Base as IntSet
+import Data.StrictPair
+
+-- $strictness
+--
+-- This module satisfies the following strictness properties:
+--
+-- 1. Key arguments are evaluated to WHNF;
+--
+-- 2. Keys and values are evaluated to WHNF before they are stored in
+--    the map.
+--
+-- Here's an example illustrating the first property:
+--
+-- > delete undefined m  ==  undefined
+--
+-- Here are some examples that illustrate the second property:
+--
+-- > map (\ v -> undefined) m  ==  undefined      -- m is not empty
+-- > mapKeys (\ k -> undefined) m  ==  undefined  -- m is not empty
+
+{--------------------------------------------------------------------
+  Query
+--------------------------------------------------------------------}
+
+-- | /O(min(n,W))/. The expression @('findWithDefault' def k map)@
+-- returns the value at key @k@ or returns @def@ when the key is not an
+-- element of the map.
+--
+-- > findWithDefault 'x' 1 (fromList [(5,'a'), (3,'b')]) == 'x'
+-- > findWithDefault 'x' 5 (fromList [(5,'a'), (3,'b')]) == 'a'
+
+-- See IntMap.Base.Note: Local 'go' functions and capturing]
+findWithDefault :: a -> Key -> IntMap a -> a
+findWithDefault def k = k `seq` go
+  where
+    go (Bin p m l r) | nomatch k p m = def
+                     | zero k m  = go l
+                     | otherwise = go r
+    go (Tip kx x) | k == kx   = x
+                  | otherwise = def
+    go Nil = def
+
+{--------------------------------------------------------------------
+  Construction
+--------------------------------------------------------------------}
+-- | /O(1)/. A map of one element.
+--
+-- > singleton 1 'a'        == fromList [(1, 'a')]
+-- > size (singleton 1 'a') == 1
+
+singleton :: Key -> a -> IntMap a
+singleton k x
+  = x `seq` Tip k x
+{-# INLINE singleton #-}
+
+{--------------------------------------------------------------------
+  Insert
+--------------------------------------------------------------------}
+-- | /O(min(n,W))/. Insert a new key\/value pair in the map.
+-- If the key is already present in the map, the associated value is
+-- replaced with the supplied value, i.e. 'insert' is equivalent to
+-- @'insertWith' 'const'@.
+--
+-- > insert 5 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'x')]
+-- > insert 7 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+-- > insert 5 'x' empty                         == singleton 5 'x'
+
+insert :: Key -> a -> IntMap a -> IntMap a
+insert k x t = k `seq` x `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> link k (Tip k x) p t
+      | zero k m      -> Bin p m (insert k x l) r
+      | otherwise     -> Bin p m l (insert k x r)
+    Tip ky _
+      | k==ky         -> Tip k x
+      | otherwise     -> link k (Tip k x) ky t
+    Nil -> Tip k x
+
+-- right-biased insertion, used by 'union'
+-- | /O(min(n,W))/. Insert with a combining function.
+-- @'insertWith' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert @f new_value old_value@.
+--
+-- > insertWith (++) 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "xxxa")]
+-- > insertWith (++) 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWith (++) 5 "xxx" empty                         == singleton 5 "xxx"
+
+insertWith :: (a -> a -> a) -> Key -> a -> IntMap a -> IntMap a
+insertWith f k x t
+  = insertWithKey (\_ x' y' -> f x' y') k x t
+
+-- | /O(min(n,W))/. Insert with a combining function.
+-- @'insertWithKey' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert @f key new_value old_value@.
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:xxx|a")]
+-- > insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWithKey f 5 "xxx" empty                         == singleton 5 "xxx"
+--
+-- If the key exists in the map, this function is lazy in @x@ but strict
+-- in the result of @f@.
+
+insertWithKey :: (Key -> a -> a -> a) -> Key -> a -> IntMap a -> IntMap a
+insertWithKey f k x t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> link k (singleton k x) p t
+      | zero k m      -> Bin p m (insertWithKey f k x l) r
+      | otherwise     -> Bin p m l (insertWithKey f k x r)
+    Tip ky y
+      | k==ky         -> Tip k $! f k x y
+      | otherwise     -> link k (singleton k x) ky t
+    Nil -> singleton k x
+
+-- | /O(min(n,W))/. The expression (@'insertLookupWithKey' f k x map@)
+-- is a pair where the first element is equal to (@'lookup' k map@)
+-- and the second element equal to (@'insertWithKey' f k x map@).
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:xxx|a")])
+-- > insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "xxx")])
+-- > insertLookupWithKey f 5 "xxx" empty                         == (Nothing,  singleton 5 "xxx")
+--
+-- This is how to define @insertLookup@ using @insertLookupWithKey@:
+--
+-- > let insertLookup kx x t = insertLookupWithKey (\_ a _ -> a) kx x t
+-- > insertLookup 5 "x" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "x")])
+-- > insertLookup 7 "x" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "x")])
+
+insertLookupWithKey :: (Key -> a -> a -> a) -> Key -> a -> IntMap a -> (Maybe a, IntMap a)
+insertLookupWithKey f0 k0 x0 t0 = k0 `seq` toPair $ go f0 k0 x0 t0
+  where
+    go f k x t =
+      case t of
+        Bin p m l r
+          | nomatch k p m -> Nothing :*: link k (singleton k x) p t
+          | zero k m      -> let (found :*: l') = go f k x l in (found :*: Bin p m l' r)
+          | otherwise     -> let (found :*: r') = go f k x r in (found :*: Bin p m l r')
+        Tip ky y
+          | k==ky         -> (Just y :*: (Tip k $! f k x y))
+          | otherwise     -> (Nothing :*: link k (singleton k x) ky t)
+        Nil -> Nothing :*: (singleton k x)
+
+
+{--------------------------------------------------------------------
+  Deletion
+--------------------------------------------------------------------}
+-- | /O(min(n,W))/. Adjust a value at a specific key. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjust ("new " ++) 7 empty                         == empty
+
+adjust ::  (a -> a) -> Key -> IntMap a -> IntMap a
+adjust f k m
+  = adjustWithKey (\_ x -> f x) k m
+
+-- | /O(min(n,W))/. Adjust a value at a specific key. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > let f key x = (show key) ++ ":new " ++ x
+-- > adjustWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > adjustWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjustWithKey f 7 empty                         == empty
+
+adjustWithKey ::  (Key -> a -> a) -> Key -> IntMap a -> IntMap a
+adjustWithKey f
+  = updateWithKey (\k' x -> Just (f k' x))
+
+-- | /O(min(n,W))/. The expression (@'update' f k map@) updates the value @x@
+-- at @k@ (if it is in the map). If (@f x@) is 'Nothing', the element is
+-- deleted. If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > update f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > update f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > update f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+update ::  (a -> Maybe a) -> Key -> IntMap a -> IntMap a
+update f
+  = updateWithKey (\_ x -> f x)
+
+-- | /O(min(n,W))/. The expression (@'update' f k map@) updates the value @x@
+-- at @k@ (if it is in the map). If (@f k x@) is 'Nothing', the element is
+-- deleted. If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > updateWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > updateWithKey f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateWithKey ::  (Key -> a -> Maybe a) -> Key -> IntMap a -> IntMap a
+updateWithKey f k t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> t
+      | zero k m      -> bin p m (updateWithKey f k l) r
+      | otherwise     -> bin p m l (updateWithKey f k r)
+    Tip ky y
+      | k==ky         -> case f k y of
+                           Just y' -> y' `seq` Tip ky y'
+                           Nothing -> Nil
+      | otherwise     -> t
+    Nil -> Nil
+
+-- | /O(min(n,W))/. Lookup and update.
+-- The function returns original value, if it is updated.
+-- This is different behavior than 'Data.Map.updateLookupWithKey'.
+-- Returns the original key value if the map entry is deleted.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateLookupWithKey f 5 (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:new a")])
+-- > updateLookupWithKey f 7 (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a")])
+-- > updateLookupWithKey f 3 (fromList [(5,"a"), (3,"b")]) == (Just "b", singleton 5 "a")
+
+updateLookupWithKey ::  (Key -> a -> Maybe a) -> Key -> IntMap a -> (Maybe a,IntMap a)
+updateLookupWithKey f0 k0 t0 = k0 `seq` toPair $ go f0 k0 t0
+  where
+    go f k t =
+      case t of
+        Bin p m l r
+          | nomatch k p m -> (Nothing :*: t)
+          | zero k m      -> let (found :*: l') = go f k l in (found :*: bin p m l' r)
+          | otherwise     -> let (found :*: r') = go f k r in (found :*: bin p m l r')
+        Tip ky y
+          | k==ky         -> case f k y of
+                               Just y' -> y' `seq` (Just y :*: Tip ky y')
+                               Nothing -> (Just y :*: Nil)
+          | otherwise     -> (Nothing :*: t)
+        Nil -> (Nothing :*: Nil)
+
+
+
+-- | /O(log n)/. The expression (@'alter' f k map@) alters the value @x@ at @k@, or absence thereof.
+-- 'alter' can be used to insert, delete, or update a value in an 'IntMap'.
+-- In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.
+alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
+alter f k t = k `seq`
+  case t of
+    Bin p m l r
+      | nomatch k p m -> case f Nothing of
+                           Nothing -> t
+                           Just x  -> x `seq` link k (Tip k x) p t
+      | zero k m      -> bin p m (alter f k l) r
+      | otherwise     -> bin p m l (alter f k r)
+    Tip ky y
+      | k==ky         -> case f (Just y) of
+                           Just  x -> x `seq` Tip ky x
+                           Nothing -> Nil
+      | otherwise     -> case f Nothing of
+                           Just x  -> x `seq` link k (Tip k x) ky t
+                           Nothing -> t
+    Nil               -> case f Nothing of
+                           Just x  -> x `seq` Tip k x
+                           Nothing -> Nil
+
+
+{--------------------------------------------------------------------
+  Union
+--------------------------------------------------------------------}
+-- | The union of a list of maps, with a combining operation.
+--
+-- > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+-- >     == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
+
+unionsWith :: (a->a->a) -> [IntMap a] -> IntMap a
+unionsWith f ts
+  = foldlStrict (unionWith f) empty ts
+
+-- | /O(n+m)/. The union with a combining function.
+--
+-- > unionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "aA"), (7, "C")]
+
+unionWith :: (a -> a -> a) -> IntMap a -> IntMap a -> IntMap a
+unionWith f m1 m2
+  = unionWithKey (\_ x y -> f x y) m1 m2
+
+-- | /O(n+m)/. The union with a combining function.
+--
+-- > let f key left_value right_value = (show key) ++ ":" ++ left_value ++ "|" ++ right_value
+-- > unionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "5:a|A"), (7, "C")]
+
+unionWithKey :: (Key -> a -> a -> a) -> IntMap a -> IntMap a -> IntMap a
+unionWithKey f m1 m2
+  = mergeWithKey' Bin (\(Tip k1 x1) (Tip _k2 x2) -> Tip k1 $! f k1 x1 x2) id id m1 m2
+
+{--------------------------------------------------------------------
+  Difference
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. Difference with a combining function.
+--
+-- > let f al ar = if al == "b" then Just (al ++ ":" ++ ar) else Nothing
+-- > differenceWith f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (7, "C")])
+-- >     == singleton 3 "b:B"
+
+differenceWith :: (a -> b -> Maybe a) -> IntMap a -> IntMap b -> IntMap a
+differenceWith f m1 m2
+  = differenceWithKey (\_ x y -> f x y) m1 m2
+
+-- | /O(n+m)/. Difference with a combining function. When two equal keys are
+-- encountered, the combining function is applied to the key and both values.
+-- If it returns 'Nothing', the element is discarded (proper set difference).
+-- If it returns (@'Just' y@), the element is updated with a new value @y@.
+--
+-- > let f k al ar = if al == "b" then Just ((show k) ++ ":" ++ al ++ "|" ++ ar) else Nothing
+-- > differenceWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (10, "C")])
+-- >     == singleton 3 "3:b|B"
+
+differenceWithKey :: (Key -> a -> b -> Maybe a) -> IntMap a -> IntMap b -> IntMap a
+differenceWithKey f m1 m2
+  = mergeWithKey f id (const Nil) m1 m2
+
+{--------------------------------------------------------------------
+  Intersection
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. The intersection with a combining function.
+--
+-- > intersectionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "aA"
+
+intersectionWith :: (a -> b -> c) -> IntMap a -> IntMap b -> IntMap c
+intersectionWith f m1 m2
+  = intersectionWithKey (\_ x y -> f x y) m1 m2
+
+-- | /O(n+m)/. The intersection with a combining function.
+--
+-- > let f k al ar = (show k) ++ ":" ++ al ++ "|" ++ ar
+-- > intersectionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "5:a|A"
+
+intersectionWithKey :: (Key -> a -> b -> c) -> IntMap a -> IntMap b -> IntMap c
+intersectionWithKey f m1 m2
+  = mergeWithKey' bin (\(Tip k1 x1) (Tip _k2 x2) -> Tip k1 $! f k1 x1 x2) (const Nil) (const Nil) m1 m2
+
+{--------------------------------------------------------------------
+  MergeWithKey
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. A high-performance universal combining function. Using
+-- 'mergeWithKey', all combining functions can be defined without any loss of
+-- efficiency (with exception of 'union', 'difference' and 'intersection',
+-- where sharing of some nodes is lost with 'mergeWithKey').
+--
+-- Please make sure you know what is going on when using 'mergeWithKey',
+-- otherwise you can be surprised by unexpected code growth or even
+-- corruption of the data structure.
+--
+-- When 'mergeWithKey' is given three arguments, it is inlined to the call
+-- site. You should therefore use 'mergeWithKey' only to define your custom
+-- combining functions. For example, you could define 'unionWithKey',
+-- 'differenceWithKey' and 'intersectionWithKey' as
+--
+-- > myUnionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) id id m1 m2
+-- > myDifferenceWithKey f m1 m2 = mergeWithKey f id (const empty) m1 m2
+-- > myIntersectionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) (const empty) (const empty) m1 m2
+--
+-- When calling @'mergeWithKey' combine only1 only2@, a function combining two
+-- 'IntMap's is created, such that
+--
+-- * if a key is present in both maps, it is passed with both corresponding
+--   values to the @combine@ function. Depending on the result, the key is either
+--   present in the result with specified value, or is left out;
+--
+-- * a nonempty subtree present only in the first map is passed to @only1@ and
+--   the output is added to the result;
+--
+-- * a nonempty subtree present only in the second map is passed to @only2@ and
+--   the output is added to the result.
+--
+-- The @only1@ and @only2@ methods /must return a map with a subset (possibly empty) of the keys of the given map/.
+-- The values can be modified arbitrarily.  Most common variants of @only1@ and
+-- @only2@ are 'id' and @'const' 'empty'@, but for example @'map' f@ or
+-- @'filterWithKey' f@ could be used for any @f@.
+
+mergeWithKey :: (Key -> a -> b -> Maybe c) -> (IntMap a -> IntMap c) -> (IntMap b -> IntMap c)
+             -> IntMap a -> IntMap b -> IntMap c
+mergeWithKey f g1 g2 = mergeWithKey' bin combine g1 g2
+  where -- We use the lambda form to avoid non-exhaustive pattern matches warning.
+        combine = \(Tip k1 x1) (Tip _k2 x2) -> case f k1 x1 x2 of Nothing -> Nil
+                                                                  Just x -> x `seq` Tip k1 x
+        {-# INLINE combine #-}
+{-# INLINE mergeWithKey #-}
+
+{--------------------------------------------------------------------
+  Min\/Max
+--------------------------------------------------------------------}
+
+-- | /O(log n)/. Update the value at the minimal key.
+--
+-- > updateMinWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"3:b"), (5,"a")]
+-- > updateMinWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMinWithKey :: (Key -> a -> Maybe a) -> IntMap a -> IntMap a
+updateMinWithKey f t =
+  case t of Bin p m l r | m < 0 -> bin p m l (go f r)
+            _ -> go f t
+  where
+    go f' (Bin p m l r) = bin p m (go f' l) r
+    go f' (Tip k y) = case f' k y of
+                        Just y' -> y' `seq` Tip k y'
+                        Nothing -> Nil
+    go _ Nil = error "updateMinWithKey Nil"
+
+-- | /O(log n)/. Update the value at the maximal key.
+--
+-- > updateMaxWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"b"), (5,"5:a")]
+-- > updateMaxWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMaxWithKey :: (Key -> a -> Maybe a) -> IntMap a -> IntMap a
+updateMaxWithKey f t =
+  case t of Bin p m l r | m < 0 -> bin p m (go f l) r
+            _ -> go f t
+  where
+    go f' (Bin p m l r) = bin p m l (go f' r)
+    go f' (Tip k y) = case f' k y of
+                        Just y' -> y' `seq` Tip k y'
+                        Nothing -> Nil
+    go _ Nil = error "updateMaxWithKey Nil"
+
+-- | /O(log n)/. Update the value at the maximal key.
+--
+-- > updateMax (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "Xa")]
+-- > updateMax (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMax :: (a -> Maybe a) -> IntMap a -> IntMap a
+updateMax f = updateMaxWithKey (const f)
+
+-- | /O(log n)/. Update the value at the minimal key.
+--
+-- > updateMin (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "Xb"), (5, "a")]
+-- > updateMin (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMin :: (a -> Maybe a) -> IntMap a -> IntMap a
+updateMin f = updateMinWithKey (const f)
+
+
+{--------------------------------------------------------------------
+  Mapping
+--------------------------------------------------------------------}
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > map (++ "x") (fromList [(5,"a"), (3,"b")]) == fromList [(3, "bx"), (5, "ax")]
+
+map :: (a -> b) -> IntMap a -> IntMap b
+map f t
+  = case t of
+      Bin p m l r -> Bin p m (map f l) (map f r)
+      Tip k x     -> Tip k $! f x
+      Nil         -> Nil
+
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > let f key x = (show key) ++ ":" ++ x
+-- > mapWithKey f (fromList [(5,"a"), (3,"b")]) == fromList [(3, "3:b"), (5, "5:a")]
+
+mapWithKey :: (Key -> a -> b) -> IntMap a -> IntMap b
+mapWithKey f t
+  = case t of
+      Bin p m l r -> Bin p m (mapWithKey f l) (mapWithKey f r)
+      Tip k x     -> Tip k $! f k x
+      Nil         -> Nil
+
+-- | /O(n)/. The function @'mapAccum'@ threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a b = (a ++ b, b ++ "X")
+-- > mapAccum f "Everything: " (fromList [(5,"a"), (3,"b")]) == ("Everything: ba", fromList [(3, "bX"), (5, "aX")])
+
+mapAccum :: (a -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccum f = mapAccumWithKey (\a' _ x -> f a' x)
+
+-- | /O(n)/. The function @'mapAccumWithKey'@ threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+-- > mapAccumWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) == ("Everything: 3-b 5-a", fromList [(3, "bX"), (5, "aX")])
+
+mapAccumWithKey :: (a -> Key -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccumWithKey f a t
+  = mapAccumL f a t
+
+-- | /O(n)/. The function @'mapAccumL'@ threads an accumulating
+-- argument through the map in ascending order of keys.  Strict in
+-- the accumulating argument and the both elements of the
+-- result of the function.
+mapAccumL :: (a -> Key -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccumL f0 a0 t0 = toPair $ go f0 a0 t0
+  where
+    go f a t
+      = case t of
+          Bin p m l r -> let (a1 :*: l') = go f a l
+                             (a2 :*: r') = go f a1 r
+                         in (a2 :*: Bin p m l' r')
+          Tip k x     -> let (a',x') = f a k x in x' `seq` (a' :*: Tip k x')
+          Nil         -> (a :*: Nil)
+
+-- | /O(n)/. The function @'mapAccumR'@ threads an accumulating
+-- argument through the map in descending order of keys.
+mapAccumRWithKey :: (a -> Key -> b -> (a,c)) -> a -> IntMap b -> (a,IntMap c)
+mapAccumRWithKey f0 a0 t0 = toPair $ go f0 a0 t0
+  where
+    go f a t
+      = case t of
+          Bin p m l r -> let (a1 :*: r') = go f a r
+                             (a2 :*: l') = go f a1 l
+                         in (a2 :*: Bin p m l' r')
+          Tip k x     -> let (a',x') = f a k x in x' `seq` (a' :*: Tip k x')
+          Nil         -> (a :*: Nil)
+
+-- | /O(n*log n)/.
+-- @'mapKeysWith' c f s@ is the map obtained by applying @f@ to each key of @s@.
+--
+-- The size of the result may be smaller if @f@ maps two or more distinct
+-- keys to the same new key.  In this case the associated values will be
+-- combined using @c@.
+--
+-- > mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "cdab"
+-- > mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "cdab"
+
+mapKeysWith :: (a -> a -> a) -> (Key->Key) -> IntMap a -> IntMap a
+mapKeysWith c f = fromListWith c . foldrWithKey (\k x xs -> (f k, x) : xs) []
+
+{--------------------------------------------------------------------
+  Filter
+--------------------------------------------------------------------}
+-- | /O(n)/. Map values and collect the 'Just' results.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > mapMaybe f (fromList [(5,"a"), (3,"b")]) == singleton 5 "new a"
+
+mapMaybe :: (a -> Maybe b) -> IntMap a -> IntMap b
+mapMaybe f = mapMaybeWithKey (\_ x -> f x)
+
+-- | /O(n)/. Map keys\/values and collect the 'Just' results.
+--
+-- > let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
+-- > mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
+
+mapMaybeWithKey :: (Key -> a -> Maybe b) -> IntMap a -> IntMap b
+mapMaybeWithKey f (Bin p m l r)
+  = bin p m (mapMaybeWithKey f l) (mapMaybeWithKey f r)
+mapMaybeWithKey f (Tip k x) = case f k x of
+  Just y  -> y `seq` Tip k y
+  Nothing -> Nil
+mapMaybeWithKey _ Nil = Nil
+
+-- | /O(n)/. Map values and separate the 'Left' and 'Right' results.
+--
+-- > let f a = if a < "c" then Left a else Right a
+-- > mapEither f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(3,"b"), (5,"a")], fromList [(1,"x"), (7,"z")])
+-- >
+-- > mapEither (\ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+
+mapEither :: (a -> Either b c) -> IntMap a -> (IntMap b, IntMap c)
+mapEither f m
+  = mapEitherWithKey (\_ x -> f x) m
+
+-- | /O(n)/. Map keys\/values and separate the 'Left' and 'Right' results.
+--
+-- > let f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
+-- > mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])
+-- >
+-- > mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])
+
+mapEitherWithKey :: (Key -> a -> Either b c) -> IntMap a -> (IntMap b, IntMap c)
+mapEitherWithKey f0 t0 = toPair $ go f0 t0
+  where
+    go f (Bin p m l r)
+      = bin p m l1 r1 :*: bin p m l2 r2
+      where
+        (l1 :*: l2) = go f l
+        (r1 :*: r2) = go f r
+    go f (Tip k x) = case f k x of
+      Left y  -> y `seq` (Tip k y :*: Nil)
+      Right z -> z `seq` (Nil :*: Tip k z)
+    go _ Nil = (Nil :*: Nil)
+
+{--------------------------------------------------------------------
+  Conversions
+--------------------------------------------------------------------}
+
+-- | /O(n)/. Build a map from a set of keys and a function which for each key
+-- computes its value.
+--
+-- > fromSet (\k -> replicate k 'a') (Data.IntSet.fromList [3, 5]) == fromList [(5,"aaaaa"), (3,"aaa")]
+-- > fromSet undefined Data.IntSet.empty == empty
+
+fromSet :: (Key -> a) -> IntSet.IntSet -> IntMap a
+fromSet _ IntSet.Nil = Nil
+fromSet f (IntSet.Bin p m l r) = Bin p m (fromSet f l) (fromSet f r)
+fromSet f (IntSet.Tip kx bm) = buildTree f kx bm (IntSet.suffixBitMask + 1)
+  where -- This is slightly complicated, as we to convert the dense
+        -- representation of IntSet into tree representation of IntMap.
+        --
+        -- We are given a nonzero bit mask 'bmask' of 'bits' bits with prefix 'prefix'.
+        -- We split bmask into halves corresponding to left and right subtree.
+        -- If they are both nonempty, we create a Bin node, otherwise exactly
+        -- one of them is nonempty and we construct the IntMap from that half.
+        buildTree g prefix bmask bits = prefix `seq` bmask `seq` case bits of
+          0 -> Tip prefix $! g prefix
+          _ -> case intFromNat ((natFromInt bits) `shiftRL` 1) of
+                 bits2 | bmask .&. ((1 `shiftLL` bits2) - 1) == 0 ->
+                           buildTree g (prefix + bits2) (bmask `shiftRL` bits2) bits2
+                       | (bmask `shiftRL` bits2) .&. ((1 `shiftLL` bits2) - 1) == 0 ->
+                           buildTree g prefix bmask bits2
+                       | otherwise ->
+                           Bin prefix bits2 (buildTree g prefix bmask bits2) (buildTree g (prefix + bits2) (bmask `shiftRL` bits2) bits2)
+
+{--------------------------------------------------------------------
+  Lists
+--------------------------------------------------------------------}
+-- | /O(n*min(n,W))/. Create a map from a list of key\/value pairs.
+--
+-- > fromList [] == empty
+-- > fromList [(5,"a"), (3,"b"), (5, "c")] == fromList [(5,"c"), (3,"b")]
+-- > fromList [(5,"c"), (3,"b"), (5, "a")] == fromList [(5,"a"), (3,"b")]
+
+fromList :: [(Key,a)] -> IntMap a
+fromList xs
+  = foldlStrict ins empty xs
+  where
+    ins t (k,x)  = insert k x t
+
+-- | /O(n*min(n,W))/. Create a map from a list of key\/value pairs with a combining function. See also 'fromAscListWith'.
+--
+-- > fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] == fromList [(3, "ab"), (5, "aba")]
+-- > fromListWith (++) [] == empty
+
+fromListWith :: (a -> a -> a) -> [(Key,a)] -> IntMap a
+fromListWith f xs
+  = fromListWithKey (\_ x y -> f x y) xs
+
+-- | /O(n*min(n,W))/. Build a map from a list of key\/value pairs with a combining function. See also fromAscListWithKey'.
+--
+-- > fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] == fromList [(3, "ab"), (5, "aba")]
+-- > fromListWith (++) [] == empty
+
+fromListWithKey :: (Key -> a -> a -> a) -> [(Key,a)] -> IntMap a
+fromListWithKey f xs
+  = foldlStrict ins empty xs
+  where
+    ins t (k,x) = insertWithKey f k x t
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order.
+--
+-- > fromAscList [(3,"b"), (5,"a")]          == fromList [(3, "b"), (5, "a")]
+-- > fromAscList [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "b")]
+
+fromAscList :: [(Key,a)] -> IntMap a
+fromAscList xs
+  = fromAscListWithKey (\_ x _ -> x) xs
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order, with a combining function on equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "ba")]
+
+fromAscListWith :: (a -> a -> a) -> [(Key,a)] -> IntMap a
+fromAscListWith f xs
+  = fromAscListWithKey (\_ x y -> f x y) xs
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order, with a combining function on equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "ba")]
+
+fromAscListWithKey :: (Key -> a -> a -> a) -> [(Key,a)] -> IntMap a
+fromAscListWithKey _ []         = Nil
+fromAscListWithKey f (x0 : xs0) = fromDistinctAscList (combineEq x0 xs0)
+  where
+    -- [combineEq f xs] combines equal elements with function [f] in an ordered list [xs]
+    combineEq z [] = [z]
+    combineEq z@(kz,zz) (x@(kx,xx):xs)
+      | kx==kz    = let yy = f kx xx zz in yy `seq` combineEq (kx,yy) xs
+      | otherwise = z:combineEq x xs
+
+-- | /O(n)/. Build a map from a list of key\/value pairs where
+-- the keys are in ascending order and all distinct.
+-- /The precondition (input list is strictly ascending) is not checked./
+--
+-- > fromDistinctAscList [(3,"b"), (5,"a")] == fromList [(3, "b"), (5, "a")]
+
+fromDistinctAscList :: [(Key,a)] -> IntMap a
+fromDistinctAscList []         = Nil
+fromDistinctAscList (z0 : zs0) = work z0 zs0 Nada
+  where
+    work (kx,vx) []            stk = vx `seq` finish kx (Tip kx vx) stk
+    work (kx,vx) (z@(kz,_):zs) stk = vx `seq` reduce z zs (branchMask kx kz) kx (Tip kx vx) stk
+
+    reduce :: (Key,a) -> [(Key,a)] -> Mask -> Prefix -> IntMap a -> Stack a -> IntMap a
+    reduce z zs _ px tx Nada = work z zs (Push px tx Nada)
+    reduce z zs m px tx stk@(Push py ty stk') =
+        let mxy = branchMask px py
+            pxy = mask px mxy
+        in  if shorter m mxy
+                 then reduce z zs m pxy (Bin pxy mxy ty tx) stk'
+                 else work z zs (Push px tx stk)
+
+    finish _  t  Nada = t
+    finish px tx (Push py ty stk) = finish p (link py ty px tx) stk
+        where m = branchMask px py
+              p = mask px m
+
+data Stack a = Push {-# UNPACK #-} !Prefix !(IntMap a) !(Stack a) | Nada
diff --git a/Data/IntSet.hs b/Data/IntSet.hs
new file mode 100644
--- /dev/null
+++ b/Data/IntSet.hs
@@ -0,0 +1,150 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Safe #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.IntSet
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Joachim Breitner 2011
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of integer sets.
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.IntSet (IntSet)
+-- >  import qualified Data.IntSet as IntSet
+--
+-- The implementation is based on /big-endian patricia trees/.  This data
+-- structure performs especially well on binary operations like 'union'
+-- and 'intersection'.  However, my benchmarks show that it is also
+-- (much) faster on insertions and deletions when compared to a generic
+-- size-balanced set implementation (see "Data.Set").
+--
+--    * Chris Okasaki and Andy Gill,  \"/Fast Mergeable Integer Maps/\",
+--      Workshop on ML, September 1998, pages 77-86,
+--      <http://citeseer.ist.psu.edu/okasaki98fast.html>
+--
+--    * D.R. Morrison, \"/PATRICIA -- Practical Algorithm To Retrieve
+--      Information Coded In Alphanumeric/\", Journal of the ACM, 15(4),
+--      October 1968, pages 514-534.
+--
+-- Additionally, this implementation places bitmaps in the leaves of the tree.
+-- Their size is the natural size of a machine word (32 or 64 bits) and greatly
+-- reduce memory footprint and execution times for dense sets, e.g. sets where
+-- it is likely that many values lie close to each other. The asymptotics are
+-- not affected by this optimization.
+--
+-- Many operations have a worst-case complexity of /O(min(n,W))/.
+-- This means that the operation can become linear in the number of
+-- elements with a maximum of /W/ -- the number of bits in an 'Int'
+-- (32 or 64).
+-----------------------------------------------------------------------------
+
+module Data.IntSet (
+            -- * Strictness properties
+            -- $strictness
+
+            -- * Set type
+#if !defined(TESTING)
+              IntSet          -- instance Eq,Show
+#else
+              IntSet(..)      -- instance Eq,Show
+#endif
+            , Key
+
+            -- * Operators
+            , (\\)
+
+            -- * Query
+            , IS.null
+            , size
+            , member
+            , notMember
+            , lookupLT
+            , lookupGT
+            , lookupLE
+            , lookupGE
+            , isSubsetOf
+            , isProperSubsetOf
+
+            -- * Construction
+            , empty
+            , singleton
+            , insert
+            , delete
+
+            -- * Combine
+            , union
+            , unions
+            , difference
+            , intersection
+
+            -- * Filter
+            , IS.filter
+            , partition
+            , split
+            , splitMember
+            , splitRoot
+
+            -- * Map
+            , IS.map
+
+            -- * Folds
+            , IS.foldr
+            , IS.foldl
+            -- ** Strict folds
+            , foldr'
+            , foldl'
+            -- ** Legacy folds
+            , fold
+
+            -- * Min\/Max
+            , findMin
+            , findMax
+            , deleteMin
+            , deleteMax
+            , deleteFindMin
+            , deleteFindMax
+            , maxView
+            , minView
+
+            -- * Conversion
+
+            -- ** List
+            , elems
+            , toList
+            , fromList
+
+            -- ** Ordered list
+            , toAscList
+            , toDescList
+            , fromAscList
+            , fromDistinctAscList
+
+            -- * Debugging
+            , showTree
+            , showTreeWith
+
+#if defined(TESTING)
+            -- * Internals
+            , match
+#endif
+            ) where
+
+import Data.IntSet.Base as IS
+
+-- $strictness
+--
+-- This module satisfies the following strictness property:
+--
+-- * Key arguments are evaluated to WHNF
+--
+-- Here are some examples that illustrate the property:
+--
+-- > delete undefined s  ==  undefined
diff --git a/Data/IntSet/Base.hs b/Data/IntSet/Base.hs
new file mode 100644
--- /dev/null
+++ b/Data/IntSet/Base.hs
@@ -0,0 +1,1534 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE MagicHash, BangPatterns, DeriveDataTypeable, StandaloneDeriving #-}
+#endif
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE TypeFamilies #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.IntSet.Base
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Joachim Breitner 2011
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of integer sets.
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.IntSet (IntSet)
+-- >  import qualified Data.IntSet as IntSet
+--
+-- The implementation is based on /big-endian patricia trees/.  This data
+-- structure performs especially well on binary operations like 'union'
+-- and 'intersection'.  However, my benchmarks show that it is also
+-- (much) faster on insertions and deletions when compared to a generic
+-- size-balanced set implementation (see "Data.Set").
+--
+--    * Chris Okasaki and Andy Gill,  \"/Fast Mergeable Integer Maps/\",
+--      Workshop on ML, September 1998, pages 77-86,
+--      <http://citeseer.ist.psu.edu/okasaki98fast.html>
+--
+--    * D.R. Morrison, \"/PATRICIA -- Practical Algorithm To Retrieve
+--      Information Coded In Alphanumeric/\", Journal of the ACM, 15(4),
+--      October 1968, pages 514-534.
+--
+-- Additionally, this implementation places bitmaps in the leaves of the tree.
+-- Their size is the natural size of a machine word (32 or 64 bits) and greatly
+-- reduce memory footprint and execution times for dense sets, e.g. sets where
+-- it is likely that many values lie close to each other. The asymptotics are
+-- not affected by this optimization.
+--
+-- Many operations have a worst-case complexity of /O(min(n,W))/.
+-- This means that the operation can become linear in the number of
+-- elements with a maximum of /W/ -- the number of bits in an 'Int'
+-- (32 or 64).
+-----------------------------------------------------------------------------
+
+-- [Note: INLINE bit fiddling]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- It is essential that the bit fiddling functions like mask, zero, branchMask
+-- etc are inlined. If they do not, the memory allocation skyrockets. The GHC
+-- usually gets it right, but it is disastrous if it does not. Therefore we
+-- explicitly mark these functions INLINE.
+
+
+-- [Note: Local 'go' functions and capturing]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- Care must be taken when using 'go' function which captures an argument.
+-- Sometimes (for example when the argument is passed to a data constructor,
+-- as in insert), GHC heap-allocates more than necessary. Therefore C-- code
+-- must be checked for increased allocation when creating and modifying such
+-- functions.
+
+
+-- [Note: Order of constructors]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- The order of constructors of IntSet matters when considering performance.
+-- Currently in GHC 7.0, when type has 3 constructors, they are matched from
+-- the first to the last -- the best performance is achieved when the
+-- constructors are ordered by frequency.
+-- On GHC 7.0, reordering constructors from Nil | Tip | Bin to Bin | Tip | Nil
+-- improves the benchmark by circa 10%.
+
+module Data.IntSet.Base (
+    -- * Set type
+      IntSet(..), Key -- instance Eq,Show
+
+    -- * Operators
+    , (\\)
+
+    -- * Query
+    , null
+    , size
+    , member
+    , notMember
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+    , isSubsetOf
+    , isProperSubsetOf
+
+    -- * Construction
+    , empty
+    , singleton
+    , insert
+    , delete
+
+    -- * Combine
+    , union
+    , unions
+    , difference
+    , intersection
+
+    -- * Filter
+    , filter
+    , partition
+    , split
+    , splitMember
+    , splitRoot
+
+    -- * Map
+    , map
+
+    -- * Folds
+    , foldr
+    , foldl
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    -- ** Legacy folds
+    , fold
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , maxView
+    , minView
+
+    -- * Conversion
+
+    -- ** List
+    , elems
+    , toList
+    , fromList
+
+    -- ** Ordered list
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromDistinctAscList
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+
+    -- * Internals
+    , match
+    , suffixBitMask
+    , prefixBitMask
+    , bitmapOf
+    ) where
+
+-- We want to be able to compile without cabal. Nevertheless
+-- #if defined(MIN_VERSION_base) && MIN_VERSION_base(4,5,0)
+-- does not work, because if MIN_VERSION_base is undefined,
+-- the last condition is syntactically wrong.
+#define MIN_VERSION_base_4_5_0 0
+#ifdef MIN_VERSION_base
+#if MIN_VERSION_base(4,5,0)
+#undef MIN_VERSION_base_4_5_0
+#define MIN_VERSION_base_4_5_0 1
+#endif
+#endif
+
+#define MIN_VERSION_base_4_7_0 0
+#ifdef MIN_VERSION_base
+#if MIN_VERSION_base(4,7,0)
+#undef MIN_VERSION_base_4_7_0
+#define MIN_VERSION_base_4_7_0 1
+#endif
+#endif
+
+import Control.DeepSeq (NFData)
+import Data.Bits
+import qualified Data.List as List
+import Data.Maybe (fromMaybe)
+import Data.Monoid (Monoid(..))
+import Data.Typeable
+import Data.Word (Word)
+import Prelude hiding (filter, foldr, foldl, null, map)
+
+import Data.BitUtil
+import Data.StrictPair
+
+#if __GLASGOW_HASKELL__
+import Data.Data (Data(..), Constr, mkConstr, constrIndex, Fixity(Prefix), DataType, mkDataType)
+import Text.Read
+#endif
+
+#if __GLASGOW_HASKELL__
+import GHC.Exts (Int(..), build)
+#if __GLASGOW_HASKELL__ >= 708
+import qualified GHC.Exts as GHCExts
+#endif
+import GHC.Prim (indexInt8OffAddr#)
+#endif
+
+-- On GHC, include MachDeps.h to get WORD_SIZE_IN_BITS macro.
+#if defined(__GLASGOW_HASKELL__)
+# include "MachDeps.h"
+#endif
+
+-- Use macros to define strictness of functions.
+-- STRICT_x_OF_y denotes an y-ary function strict in the x-th parameter.
+-- We do not use BangPatterns, because they are not in any standard and we
+-- want the compilers to be compiled by as many compilers as possible.
+#define STRICT_1_OF_2(fn) fn arg _ | arg `seq` False = undefined
+#define STRICT_2_OF_2(fn) fn _ arg | arg `seq` False = undefined
+#define STRICT_1_OF_3(fn) fn arg _ _ | arg `seq` False = undefined
+#define STRICT_2_OF_3(fn) fn _ arg _ | arg `seq` False = undefined
+
+infixl 9 \\{-This comment teaches CPP correct behaviour -}
+
+-- A "Nat" is a natural machine word (an unsigned Int)
+type Nat = Word
+
+natFromInt :: Int -> Nat
+natFromInt i = fromIntegral i
+{-# INLINE natFromInt #-}
+
+intFromNat :: Nat -> Int
+intFromNat w = fromIntegral w
+{-# INLINE intFromNat #-}
+
+{--------------------------------------------------------------------
+  Operators
+--------------------------------------------------------------------}
+-- | /O(n+m)/. See 'difference'.
+(\\) :: IntSet -> IntSet -> IntSet
+m1 \\ m2 = difference m1 m2
+
+{--------------------------------------------------------------------
+  Types
+--------------------------------------------------------------------}
+
+-- | A set of integers.
+
+-- See Note: Order of constructors
+data IntSet = Bin {-# UNPACK #-} !Prefix {-# UNPACK #-} !Mask !IntSet !IntSet
+-- Invariant: Nil is never found as a child of Bin.
+-- Invariant: The Mask is a power of 2.  It is the largest bit position at which
+--            two elements of the set differ.
+-- Invariant: Prefix is the common high-order bits that all elements share to
+--            the left of the Mask bit.
+-- Invariant: In Bin prefix mask left right, left consists of the elements that
+--            don't have the mask bit set; right is all the elements that do.
+            | Tip {-# UNPACK #-} !Prefix {-# UNPACK #-} !BitMap
+-- Invariant: The Prefix is zero for all but the last 5 (on 32 bit arches) or 6
+--            bits (on 64 bit arches). The values of the map represented by a tip
+--            are the prefix plus the indices of the set bits in the bit map.
+            | Nil
+
+-- A number stored in a set is stored as
+-- * Prefix (all but last 5-6 bits) and
+-- * BitMap (last 5-6 bits stored as a bitmask)
+--   Last 5-6 bits are called a Suffix.
+
+type Prefix = Int
+type Mask   = Int
+type BitMap = Word
+type Key    = Int
+
+instance Monoid IntSet where
+    mempty  = empty
+    mappend = union
+    mconcat = unions
+
+#if __GLASGOW_HASKELL__
+
+{--------------------------------------------------------------------
+  A Data instance
+--------------------------------------------------------------------}
+
+-- This instance preserves data abstraction at the cost of inefficiency.
+-- We provide limited reflection services for the sake of data abstraction.
+
+instance Data IntSet where
+  gfoldl f z is = z fromList `f` (toList is)
+  toConstr _     = fromListConstr
+  gunfold k z c  = case constrIndex c of
+    1 -> k (z fromList)
+    _ -> error "gunfold"
+  dataTypeOf _   = intSetDataType
+
+fromListConstr :: Constr
+fromListConstr = mkConstr intSetDataType "fromList" [] Prefix
+
+intSetDataType :: DataType
+intSetDataType = mkDataType "Data.IntSet.Base.IntSet" [fromListConstr]
+
+#endif
+
+{--------------------------------------------------------------------
+  Query
+--------------------------------------------------------------------}
+-- | /O(1)/. Is the set empty?
+null :: IntSet -> Bool
+null Nil = True
+null _   = False
+{-# INLINE null #-}
+
+-- | /O(n)/. Cardinality of the set.
+size :: IntSet -> Int
+size t
+  = case t of
+      Bin _ _ l r -> size l + size r
+      Tip _ bm -> bitcount 0 bm
+      Nil   -> 0
+
+-- | /O(min(n,W))/. Is the value a member of the set?
+
+-- See Note: Local 'go' functions and capturing]
+member :: Key -> IntSet -> Bool
+member x = x `seq` go
+  where
+    go (Bin p m l r)
+      | nomatch x p m = False
+      | zero x m      = go l
+      | otherwise     = go r
+    go (Tip y bm) = prefixOf x == y && bitmapOf x .&. bm /= 0
+    go Nil = False
+
+infix 4 `member`
+
+-- | /O(min(n,W))/. Is the element not in the set?
+notMember :: Key -> IntSet -> Bool
+notMember k = not . member k
+
+infix 4 `notMember`
+
+-- | /O(log n)/. Find largest element smaller than the given one.
+--
+-- > lookupLT 3 (fromList [3, 5]) == Nothing
+-- > lookupLT 5 (fromList [3, 5]) == Just 3
+
+-- See Note: Local 'go' functions and capturing.
+lookupLT :: Key -> IntSet -> Maybe Key
+lookupLT x t = x `seq` case t of
+    Bin _ m l r | m < 0 -> if x >= 0 then go r l else go Nil r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch x p m = if x < p then unsafeFindMax def else unsafeFindMax r
+                         | zero x m  = go def l
+                         | otherwise = go l r
+    go def (Tip kx bm) | prefixOf x > kx = Just $ kx + highestBitSet bm
+                       | prefixOf x == kx && maskLT /= 0 = Just $ kx + highestBitSet maskLT
+                       | otherwise = unsafeFindMax def
+                       where maskLT = (bitmapOf x - 1) .&. bm
+    go def Nil = unsafeFindMax def
+
+
+-- | /O(log n)/. Find smallest element greater than the given one.
+--
+-- > lookupGT 4 (fromList [3, 5]) == Just 5
+-- > lookupGT 5 (fromList [3, 5]) == Nothing
+
+-- See Note: Local 'go' functions and capturing.
+lookupGT :: Key -> IntSet -> Maybe Key
+lookupGT x t = x `seq` case t of
+    Bin _ m l r | m < 0 -> if x >= 0 then go Nil l else go l r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch x p m = if x < p then unsafeFindMin l else unsafeFindMin def
+                         | zero x m  = go r l
+                         | otherwise = go def r
+    go def (Tip kx bm) | prefixOf x < kx = Just $ kx + lowestBitSet bm
+                       | prefixOf x == kx && maskGT /= 0 = Just $ kx + lowestBitSet maskGT
+                       | otherwise = unsafeFindMin def
+                       where maskGT = (- ((bitmapOf x) `shiftLL` 1)) .&. bm
+    go def Nil = unsafeFindMin def
+
+
+-- | /O(log n)/. Find largest element smaller or equal to the given one.
+--
+-- > lookupLE 2 (fromList [3, 5]) == Nothing
+-- > lookupLE 4 (fromList [3, 5]) == Just 3
+-- > lookupLE 5 (fromList [3, 5]) == Just 5
+
+-- See Note: Local 'go' functions and capturing.
+lookupLE :: Key -> IntSet -> Maybe Key
+lookupLE x t = x `seq` case t of
+    Bin _ m l r | m < 0 -> if x >= 0 then go r l else go Nil r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch x p m = if x < p then unsafeFindMax def else unsafeFindMax r
+                         | zero x m  = go def l
+                         | otherwise = go l r
+    go def (Tip kx bm) | prefixOf x > kx = Just $ kx + highestBitSet bm
+                       | prefixOf x == kx && maskLE /= 0 = Just $ kx + highestBitSet maskLE
+                       | otherwise = unsafeFindMax def
+                       where maskLE = (((bitmapOf x) `shiftLL` 1) - 1) .&. bm
+    go def Nil = unsafeFindMax def
+
+
+-- | /O(log n)/. Find smallest element greater or equal to the given one.
+--
+-- > lookupGE 3 (fromList [3, 5]) == Just 3
+-- > lookupGE 4 (fromList [3, 5]) == Just 5
+-- > lookupGE 6 (fromList [3, 5]) == Nothing
+
+-- See Note: Local 'go' functions and capturing.
+lookupGE :: Key -> IntSet -> Maybe Key
+lookupGE x t = x `seq` case t of
+    Bin _ m l r | m < 0 -> if x >= 0 then go Nil l else go l r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r) | nomatch x p m = if x < p then unsafeFindMin l else unsafeFindMin def
+                         | zero x m  = go r l
+                         | otherwise = go def r
+    go def (Tip kx bm) | prefixOf x < kx = Just $ kx + lowestBitSet bm
+                       | prefixOf x == kx && maskGE /= 0 = Just $ kx + lowestBitSet maskGE
+                       | otherwise = unsafeFindMin def
+                       where maskGE = (- (bitmapOf x)) .&. bm
+    go def Nil = unsafeFindMin def
+
+
+
+-- Helper function for lookupGE and lookupGT. It assumes that if a Bin node is
+-- given, it has m > 0.
+unsafeFindMin :: IntSet -> Maybe Key
+unsafeFindMin Nil = Nothing
+unsafeFindMin (Tip kx bm) = Just $ kx + lowestBitSet bm
+unsafeFindMin (Bin _ _ l _) = unsafeFindMin l
+
+-- Helper function for lookupLE and lookupLT. It assumes that if a Bin node is
+-- given, it has m > 0.
+unsafeFindMax :: IntSet -> Maybe Key
+unsafeFindMax Nil = Nothing
+unsafeFindMax (Tip kx bm) = Just $ kx + highestBitSet bm
+unsafeFindMax (Bin _ _ _ r) = unsafeFindMax r
+
+{--------------------------------------------------------------------
+  Construction
+--------------------------------------------------------------------}
+-- | /O(1)/. The empty set.
+empty :: IntSet
+empty
+  = Nil
+{-# INLINE empty #-}
+
+-- | /O(1)/. A set of one element.
+singleton :: Key -> IntSet
+singleton x
+  = Tip (prefixOf x) (bitmapOf x)
+{-# INLINE singleton #-}
+
+{--------------------------------------------------------------------
+  Insert
+--------------------------------------------------------------------}
+-- | /O(min(n,W))/. Add a value to the set. There is no left- or right bias for
+-- IntSets.
+insert :: Key -> IntSet -> IntSet
+insert x = x `seq` insertBM (prefixOf x) (bitmapOf x)
+
+-- Helper function for insert and union.
+insertBM :: Prefix -> BitMap -> IntSet -> IntSet
+insertBM kx bm t = kx `seq` bm `seq`
+  case t of
+    Bin p m l r
+      | nomatch kx p m -> link kx (Tip kx bm) p t
+      | zero kx m      -> Bin p m (insertBM kx bm l) r
+      | otherwise      -> Bin p m l (insertBM kx bm r)
+    Tip kx' bm'
+      | kx' == kx -> Tip kx' (bm .|. bm')
+      | otherwise -> link kx (Tip kx bm) kx' t
+    Nil -> Tip kx bm
+
+-- | /O(min(n,W))/. Delete a value in the set. Returns the
+-- original set when the value was not present.
+delete :: Key -> IntSet -> IntSet
+delete x = x `seq` deleteBM (prefixOf x) (bitmapOf x)
+
+-- Deletes all values mentioned in the BitMap from the set.
+-- Helper function for delete and difference.
+deleteBM :: Prefix -> BitMap -> IntSet -> IntSet
+deleteBM kx bm t = kx `seq` bm `seq`
+  case t of
+    Bin p m l r
+      | nomatch kx p m -> t
+      | zero kx m      -> bin p m (deleteBM kx bm l) r
+      | otherwise      -> bin p m l (deleteBM kx bm r)
+    Tip kx' bm'
+      | kx' == kx -> tip kx (bm' .&. complement bm)
+      | otherwise -> t
+    Nil -> Nil
+
+
+{--------------------------------------------------------------------
+  Union
+--------------------------------------------------------------------}
+-- | The union of a list of sets.
+unions :: [IntSet] -> IntSet
+unions xs
+  = foldlStrict union empty xs
+
+
+-- | /O(n+m)/. The union of two sets.
+union :: IntSet -> IntSet -> IntSet
+union t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
+  | shorter m1 m2  = union1
+  | shorter m2 m1  = union2
+  | p1 == p2       = Bin p1 m1 (union l1 l2) (union r1 r2)
+  | otherwise      = link p1 t1 p2 t2
+  where
+    union1  | nomatch p2 p1 m1  = link p1 t1 p2 t2
+            | zero p2 m1        = Bin p1 m1 (union l1 t2) r1
+            | otherwise         = Bin p1 m1 l1 (union r1 t2)
+
+    union2  | nomatch p1 p2 m2  = link p1 t1 p2 t2
+            | zero p1 m2        = Bin p2 m2 (union t1 l2) r2
+            | otherwise         = Bin p2 m2 l2 (union t1 r2)
+
+union t@(Bin _ _ _ _) (Tip kx bm) = insertBM kx bm t
+union t@(Bin _ _ _ _) Nil = t
+union (Tip kx bm) t = insertBM kx bm t
+union Nil t = t
+
+infixl 5 `union`
+
+{--------------------------------------------------------------------
+  Difference
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Difference between two sets.
+difference :: IntSet -> IntSet -> IntSet
+difference t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
+  | shorter m1 m2  = difference1
+  | shorter m2 m1  = difference2
+  | p1 == p2       = bin p1 m1 (difference l1 l2) (difference r1 r2)
+  | otherwise      = t1
+  where
+    difference1 | nomatch p2 p1 m1  = t1
+                | zero p2 m1        = bin p1 m1 (difference l1 t2) r1
+                | otherwise         = bin p1 m1 l1 (difference r1 t2)
+
+    difference2 | nomatch p1 p2 m2  = t1
+                | zero p1 m2        = difference t1 l2
+                | otherwise         = difference t1 r2
+
+difference t@(Bin _ _ _ _) (Tip kx bm) = deleteBM kx bm t
+difference t@(Bin _ _ _ _) Nil = t
+
+difference t1@(Tip kx bm) t2 = differenceTip t2
+  where differenceTip (Bin p2 m2 l2 r2) | nomatch kx p2 m2 = t1
+                                        | zero kx m2 = differenceTip l2
+                                        | otherwise = differenceTip r2
+        differenceTip (Tip kx2 bm2) | kx == kx2 = tip kx (bm .&. complement bm2)
+                                    | otherwise = t1
+        differenceTip Nil = t1
+
+difference Nil _     = Nil
+
+
+
+{--------------------------------------------------------------------
+  Intersection
+--------------------------------------------------------------------}
+-- | /O(n+m)/. The intersection of two sets.
+intersection :: IntSet -> IntSet -> IntSet
+intersection t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
+  | shorter m1 m2  = intersection1
+  | shorter m2 m1  = intersection2
+  | p1 == p2       = bin p1 m1 (intersection l1 l2) (intersection r1 r2)
+  | otherwise      = Nil
+  where
+    intersection1 | nomatch p2 p1 m1  = Nil
+                  | zero p2 m1        = intersection l1 t2
+                  | otherwise         = intersection r1 t2
+
+    intersection2 | nomatch p1 p2 m2  = Nil
+                  | zero p1 m2        = intersection t1 l2
+                  | otherwise         = intersection t1 r2
+
+intersection t1@(Bin _ _ _ _) (Tip kx2 bm2) = intersectBM t1
+  where intersectBM (Bin p1 m1 l1 r1) | nomatch kx2 p1 m1 = Nil
+                                      | zero kx2 m1       = intersectBM l1
+                                      | otherwise         = intersectBM r1
+        intersectBM (Tip kx1 bm1) | kx1 == kx2 = tip kx1 (bm1 .&. bm2)
+                                  | otherwise = Nil
+        intersectBM Nil = Nil
+
+intersection (Bin _ _ _ _) Nil = Nil
+
+intersection (Tip kx1 bm1) t2 = intersectBM t2
+  where intersectBM (Bin p2 m2 l2 r2) | nomatch kx1 p2 m2 = Nil
+                                      | zero kx1 m2       = intersectBM l2
+                                      | otherwise         = intersectBM r2
+        intersectBM (Tip kx2 bm2) | kx1 == kx2 = tip kx1 (bm1 .&. bm2)
+                                  | otherwise = Nil
+        intersectBM Nil = Nil
+
+intersection Nil _ = Nil
+
+infixl 5 `intersection`
+
+{--------------------------------------------------------------------
+  Subset
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Is this a proper subset? (ie. a subset but not equal).
+isProperSubsetOf :: IntSet -> IntSet -> Bool
+isProperSubsetOf t1 t2
+  = case subsetCmp t1 t2 of
+      LT -> True
+      _  -> False
+
+subsetCmp :: IntSet -> IntSet -> Ordering
+subsetCmp t1@(Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  | shorter m1 m2  = GT
+  | shorter m2 m1  = case subsetCmpLt of
+                       GT -> GT
+                       _  -> LT
+  | p1 == p2       = subsetCmpEq
+  | otherwise      = GT  -- disjoint
+  where
+    subsetCmpLt | nomatch p1 p2 m2  = GT
+                | zero p1 m2        = subsetCmp t1 l2
+                | otherwise         = subsetCmp t1 r2
+    subsetCmpEq = case (subsetCmp l1 l2, subsetCmp r1 r2) of
+                    (GT,_ ) -> GT
+                    (_ ,GT) -> GT
+                    (EQ,EQ) -> EQ
+                    _       -> LT
+
+subsetCmp (Bin _ _ _ _) _  = GT
+subsetCmp (Tip kx1 bm1) (Tip kx2 bm2)
+  | kx1 /= kx2                  = GT -- disjoint
+  | bm1 == bm2                  = EQ
+  | bm1 .&. complement bm2 == 0 = LT
+  | otherwise                   = GT
+subsetCmp t1@(Tip kx _) (Bin p m l r)
+  | nomatch kx p m = GT
+  | zero kx m      = case subsetCmp t1 l of GT -> GT ; _ -> LT
+  | otherwise      = case subsetCmp t1 r of GT -> GT ; _ -> LT
+subsetCmp (Tip _ _) Nil = GT -- disjoint
+subsetCmp Nil Nil = EQ
+subsetCmp Nil _   = LT
+
+-- | /O(n+m)/. Is this a subset?
+-- @(s1 `isSubsetOf` s2)@ tells whether @s1@ is a subset of @s2@.
+
+isSubsetOf :: IntSet -> IntSet -> Bool
+isSubsetOf t1@(Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  | shorter m1 m2  = False
+  | shorter m2 m1  = match p1 p2 m2 && (if zero p1 m2 then isSubsetOf t1 l2
+                                                      else isSubsetOf t1 r2)
+  | otherwise      = (p1==p2) && isSubsetOf l1 l2 && isSubsetOf r1 r2
+isSubsetOf (Bin _ _ _ _) _  = False
+isSubsetOf (Tip kx1 bm1) (Tip kx2 bm2) = kx1 == kx2 && bm1 .&. complement bm2 == 0
+isSubsetOf t1@(Tip kx _) (Bin p m l r)
+  | nomatch kx p m = False
+  | zero kx m      = isSubsetOf t1 l
+  | otherwise      = isSubsetOf t1 r
+isSubsetOf (Tip _ _) Nil = False
+isSubsetOf Nil _         = True
+
+
+{--------------------------------------------------------------------
+  Filter
+--------------------------------------------------------------------}
+-- | /O(n)/. Filter all elements that satisfy some predicate.
+filter :: (Key -> Bool) -> IntSet -> IntSet
+filter predicate t
+  = case t of
+      Bin p m l r
+        -> bin p m (filter predicate l) (filter predicate r)
+      Tip kx bm
+        -> tip kx (foldl'Bits 0 (bitPred kx) 0 bm)
+      Nil -> Nil
+  where bitPred kx bm bi | predicate (kx + bi) = bm .|. bitmapOfSuffix bi
+                         | otherwise           = bm
+        {-# INLINE bitPred #-}
+
+-- | /O(n)/. partition the set according to some predicate.
+partition :: (Key -> Bool) -> IntSet -> (IntSet,IntSet)
+partition predicate0 t0 = toPair $ go predicate0 t0
+  where
+    go predicate t
+      = case t of
+          Bin p m l r
+            -> let (l1 :*: l2) = go predicate l
+                   (r1 :*: r2) = go predicate r
+               in bin p m l1 r1 :*: bin p m l2 r2
+          Tip kx bm
+            -> let bm1 = foldl'Bits 0 (bitPred kx) 0 bm
+               in  tip kx bm1 :*: tip kx (bm `xor` bm1)
+          Nil -> (Nil :*: Nil)
+      where bitPred kx bm bi | predicate (kx + bi) = bm .|. bitmapOfSuffix bi
+                             | otherwise           = bm
+            {-# INLINE bitPred #-}
+
+
+-- | /O(min(n,W))/. The expression (@'split' x set@) is a pair @(set1,set2)@
+-- where @set1@ comprises the elements of @set@ less than @x@ and @set2@
+-- comprises the elements of @set@ greater than @x@.
+--
+-- > split 3 (fromList [1..5]) == (fromList [1,2], fromList [4,5])
+split :: Key -> IntSet -> (IntSet,IntSet)
+split x t =
+  case t of
+      Bin _ m l r
+          | m < 0 -> if x >= 0  -- handle negative numbers.
+                     then case go x l of (lt :*: gt) -> let lt' = union lt r
+                                                        in lt' `seq` (lt', gt)
+                     else case go x r of (lt :*: gt) -> let gt' = union gt l
+                                                        in gt' `seq` (lt, gt')
+      _ -> case go x t of
+          (lt :*: gt) -> (lt, gt)
+  where
+    go !x' t'@(Bin p m l r)
+        | match x' p m = if zero x' m
+                         then case go x' l of
+                             (lt :*: gt) -> lt :*: union gt r
+                         else case go x' r of
+                             (lt :*: gt) -> union lt l :*: gt
+        | otherwise   = if x' < p then (Nil :*: t')
+                        else (t' :*: Nil)
+    go x' t'@(Tip kx' bm)
+        | kx' > x'          = (Nil :*: t')
+          -- equivalent to kx' > prefixOf x'
+        | kx' < prefixOf x' = (t' :*: Nil)
+        | otherwise = tip kx' (bm .&. lowerBitmap) :*: tip kx' (bm .&. higherBitmap)
+            where lowerBitmap = bitmapOf x' - 1
+                  higherBitmap = complement (lowerBitmap + bitmapOf x')
+    go _ Nil = (Nil :*: Nil)
+
+-- | /O(min(n,W))/. Performs a 'split' but also returns whether the pivot
+-- element was found in the original set.
+splitMember :: Key -> IntSet -> (IntSet,Bool,IntSet)
+splitMember x t =
+  case t of
+      Bin _ m l r | m < 0 -> if x >= 0
+                             then case go x l of
+                                 (lt, fnd, gt) -> let lt' = union lt r
+                                                  in lt' `seq` (lt', fnd, gt)
+                             else case go x r of
+                                 (lt, fnd, gt) -> let gt' = union gt l
+                                                  in gt' `seq` (lt, fnd, gt')
+      _ -> go x t
+  where
+    go x' t'@(Bin p m l r)
+        | match x' p m = if zero x' m
+                         then case go x' l of
+                             (lt, fnd, gt) -> (lt, fnd, union gt r)
+                         else case go x' r of
+                             (lt, fnd, gt) -> (union lt l, fnd, gt)
+        | otherwise   = if x' < p then (Nil, False, t') else (t', False, Nil)
+    go x' t'@(Tip kx' bm)
+        | kx' > x'          = (Nil, False, t')
+          -- equivalent to kx' > prefixOf x'
+        | kx' < prefixOf x' = (t', False, Nil)
+        | otherwise = let lt = tip kx' (bm .&. lowerBitmap)
+                          found = (bm .&. bitmapOfx') /= 0
+                          gt = tip kx' (bm .&. higherBitmap)
+                      in lt `seq` found `seq` gt `seq` (lt, found, gt)
+            where bitmapOfx' = bitmapOf x'
+                  lowerBitmap = bitmapOfx' - 1
+                  higherBitmap = complement (lowerBitmap + bitmapOfx')
+    go _ Nil = (Nil, False, Nil)
+
+
+{----------------------------------------------------------------------
+  Min/Max
+----------------------------------------------------------------------}
+
+-- | /O(min(n,W))/. Retrieves the maximal key of the set, and the set
+-- stripped of that element, or 'Nothing' if passed an empty set.
+maxView :: IntSet -> Maybe (Key, IntSet)
+maxView t =
+  case t of Nil -> Nothing
+            Bin p m l r | m < 0 -> case go l of (result, l') -> Just (result, bin p m l' r)
+            _ -> Just (go t)
+  where
+    go (Bin p m l r) = case go r of (result, r') -> (result, bin p m l r')
+    go (Tip kx bm) = case highestBitSet bm of bi -> (kx + bi, tip kx (bm .&. complement (bitmapOfSuffix bi)))
+    go Nil = error "maxView Nil"
+
+-- | /O(min(n,W))/. Retrieves the minimal key of the set, and the set
+-- stripped of that element, or 'Nothing' if passed an empty set.
+minView :: IntSet -> Maybe (Key, IntSet)
+minView t =
+  case t of Nil -> Nothing
+            Bin p m l r | m < 0 -> case go r of (result, r') -> Just (result, bin p m l r')
+            _ -> Just (go t)
+  where
+    go (Bin p m l r) = case go l of (result, l') -> (result, bin p m l' r)
+    go (Tip kx bm) = case lowestBitSet bm of bi -> (kx + bi, tip kx (bm .&. complement (bitmapOfSuffix bi)))
+    go Nil = error "minView Nil"
+
+-- | /O(min(n,W))/. Delete and find the minimal element.
+--
+-- > deleteFindMin set = (findMin set, deleteMin set)
+deleteFindMin :: IntSet -> (Key, IntSet)
+deleteFindMin = fromMaybe (error "deleteFindMin: empty set has no minimal element") . minView
+
+-- | /O(min(n,W))/. Delete and find the maximal element.
+--
+-- > deleteFindMax set = (findMax set, deleteMax set)
+deleteFindMax :: IntSet -> (Key, IntSet)
+deleteFindMax = fromMaybe (error "deleteFindMax: empty set has no maximal element") . maxView
+
+
+-- | /O(min(n,W))/. The minimal element of the set.
+findMin :: IntSet -> Key
+findMin Nil = error "findMin: empty set has no minimal element"
+findMin (Tip kx bm) = kx + lowestBitSet bm
+findMin (Bin _ m l r)
+  |   m < 0   = find r
+  | otherwise = find l
+    where find (Tip kx bm) = kx + lowestBitSet bm
+          find (Bin _ _ l' _) = find l'
+          find Nil            = error "findMin Nil"
+
+-- | /O(min(n,W))/. The maximal element of a set.
+findMax :: IntSet -> Key
+findMax Nil = error "findMax: empty set has no maximal element"
+findMax (Tip kx bm) = kx + highestBitSet bm
+findMax (Bin _ m l r)
+  |   m < 0   = find l
+  | otherwise = find r
+    where find (Tip kx bm) = kx + highestBitSet bm
+          find (Bin _ _ _ r') = find r'
+          find Nil            = error "findMax Nil"
+
+
+-- | /O(min(n,W))/. Delete the minimal element. Returns an empty set if the set is empty.
+--
+-- Note that this is a change of behaviour for consistency with 'Data.Set.Set' &#8211;
+-- versions prior to 0.5 threw an error if the 'IntSet' was already empty.
+deleteMin :: IntSet -> IntSet
+deleteMin = maybe Nil snd . minView
+
+-- | /O(min(n,W))/. Delete the maximal element. Returns an empty set if the set is empty.
+--
+-- Note that this is a change of behaviour for consistency with 'Data.Set.Set' &#8211;
+-- versions prior to 0.5 threw an error if the 'IntSet' was already empty.
+deleteMax :: IntSet -> IntSet
+deleteMax = maybe Nil snd . maxView
+
+{----------------------------------------------------------------------
+  Map
+----------------------------------------------------------------------}
+
+-- | /O(n*min(n,W))/.
+-- @'map' f s@ is the set obtained by applying @f@ to each element of @s@.
+--
+-- It's worth noting that the size of the result may be smaller if,
+-- for some @(x,y)@, @x \/= y && f x == f y@
+
+map :: (Key -> Key) -> IntSet -> IntSet
+map f = fromList . List.map f . toList
+
+{--------------------------------------------------------------------
+  Fold
+--------------------------------------------------------------------}
+-- | /O(n)/. Fold the elements in the set using the given right-associative
+-- binary operator. This function is an equivalent of 'foldr' and is present
+-- for compatibility only.
+--
+-- /Please note that fold will be deprecated in the future and removed./
+fold :: (Key -> b -> b) -> b -> IntSet -> b
+fold = foldr
+{-# INLINE fold #-}
+
+-- | /O(n)/. Fold the elements in the set using the given right-associative
+-- binary operator, such that @'foldr' f z == 'Prelude.foldr' f z . 'toAscList'@.
+--
+-- For example,
+--
+-- > toAscList set = foldr (:) [] set
+foldr :: (Key -> b -> b) -> b -> IntSet -> b
+foldr f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z l) r -- put negative numbers before
+                        | otherwise -> go (go z r) l
+            _ -> go z t
+  where
+    go z' Nil           = z'
+    go z' (Tip kx bm)   = foldrBits kx f z' bm
+    go z' (Bin _ _ l r) = go (go z' r) l
+{-# INLINE foldr #-}
+
+-- | /O(n)/. A strict version of 'foldr'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldr' :: (Key -> b -> b) -> b -> IntSet -> b
+foldr' f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z l) r -- put negative numbers before
+                        | otherwise -> go (go z r) l
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip kx bm)   = foldr'Bits kx f z' bm
+    go z' (Bin _ _ l r) = go (go z' r) l
+{-# INLINE foldr' #-}
+
+-- | /O(n)/. Fold the elements in the set using the given left-associative
+-- binary operator, such that @'foldl' f z == 'Prelude.foldl' f z . 'toAscList'@.
+--
+-- For example,
+--
+-- > toDescList set = foldl (flip (:)) [] set
+foldl :: (a -> Key -> a) -> a -> IntSet -> a
+foldl f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z r) l -- put negative numbers before
+                        | otherwise -> go (go z l) r
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip kx bm)   = foldlBits kx f z' bm
+    go z' (Bin _ _ l r) = go (go z' l) r
+{-# INLINE foldl #-}
+
+-- | /O(n)/. A strict version of 'foldl'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldl' :: (a -> Key -> a) -> a -> IntSet -> a
+foldl' f z = \t ->      -- Use lambda t to be inlinable with two arguments only.
+  case t of Bin _ m l r | m < 0 -> go (go z r) l -- put negative numbers before
+                        | otherwise -> go (go z l) r
+            _ -> go z t
+  where
+    STRICT_1_OF_2(go)
+    go z' Nil           = z'
+    go z' (Tip kx bm)   = foldl'Bits kx f z' bm
+    go z' (Bin _ _ l r) = go (go z' l) r
+{-# INLINE foldl' #-}
+
+{--------------------------------------------------------------------
+  List variations
+--------------------------------------------------------------------}
+-- | /O(n)/. An alias of 'toAscList'. The elements of a set in ascending order.
+-- Subject to list fusion.
+elems :: IntSet -> [Key]
+elems
+  = toAscList
+
+{--------------------------------------------------------------------
+  Lists
+--------------------------------------------------------------------}
+#if __GLASGOW_HASKELL__ >= 708
+instance GHCExts.IsList IntSet where
+  type Item IntSet = Key
+  fromList = fromList
+  toList   = toList
+#endif
+
+-- | /O(n)/. Convert the set to a list of elements. Subject to list fusion.
+toList :: IntSet -> [Key]
+toList
+  = toAscList
+
+-- | /O(n)/. Convert the set to an ascending list of elements. Subject to list
+-- fusion.
+toAscList :: IntSet -> [Key]
+toAscList = foldr (:) []
+
+-- | /O(n)/. Convert the set to a descending list of elements. Subject to list
+-- fusion.
+toDescList :: IntSet -> [Key]
+toDescList = foldl (flip (:)) []
+
+-- List fusion for the list generating functions.
+#if __GLASGOW_HASKELL__
+-- The foldrFB and foldlFB are foldr and foldl equivalents, used for list fusion.
+-- They are important to convert unfused to{Asc,Desc}List back, see mapFB in prelude.
+foldrFB :: (Key -> b -> b) -> b -> IntSet -> b
+foldrFB = foldr
+{-# INLINE[0] foldrFB #-}
+foldlFB :: (a -> Key -> a) -> a -> IntSet -> a
+foldlFB = foldl
+{-# INLINE[0] foldlFB #-}
+
+-- Inline elems and toList, so that we need to fuse only toAscList.
+{-# INLINE elems #-}
+{-# INLINE toList #-}
+
+-- The fusion is enabled up to phase 2 included. If it does not succeed,
+-- convert in phase 1 the expanded to{Asc,Desc}List calls back to
+-- to{Asc,Desc}List.  In phase 0, we inline fold{lr}FB (which were used in
+-- a list fusion, otherwise it would go away in phase 1), and let compiler do
+-- whatever it wants with to{Asc,Desc}List -- it was forbidden to inline it
+-- before phase 0, otherwise the fusion rules would not fire at all.
+{-# NOINLINE[0] toAscList #-}
+{-# NOINLINE[0] toDescList #-}
+{-# RULES "IntSet.toAscList" [~1] forall s . toAscList s = build (\c n -> foldrFB c n s) #-}
+{-# RULES "IntSet.toAscListBack" [1] foldrFB (:) [] = toAscList #-}
+{-# RULES "IntSet.toDescList" [~1] forall s . toDescList s = build (\c n -> foldlFB (\xs x -> c x xs) n s) #-}
+{-# RULES "IntSet.toDescListBack" [1] foldlFB (\xs x -> x : xs) [] = toDescList #-}
+#endif
+
+
+-- | /O(n*min(n,W))/. Create a set from a list of integers.
+fromList :: [Key] -> IntSet
+fromList xs
+  = foldlStrict ins empty xs
+  where
+    ins t x  = insert x t
+
+-- | /O(n)/. Build a set from an ascending list of elements.
+-- /The precondition (input list is ascending) is not checked./
+fromAscList :: [Key] -> IntSet
+fromAscList [] = Nil
+fromAscList (x0 : xs0) = fromDistinctAscList (combineEq x0 xs0)
+  where
+    combineEq x' [] = [x']
+    combineEq x' (x:xs)
+      | x==x'     = combineEq x' xs
+      | otherwise = x' : combineEq x xs
+
+-- | /O(n)/. Build a set from an ascending list of distinct elements.
+-- /The precondition (input list is strictly ascending) is not checked./
+fromDistinctAscList :: [Key] -> IntSet
+fromDistinctAscList []         = Nil
+fromDistinctAscList (z0 : zs0) = work (prefixOf z0) (bitmapOf z0) zs0 Nada
+  where
+    -- 'work' accumulates all values that go into one tip, before passing this Tip
+    -- to 'reduce'
+    work kx bm []     stk = finish kx (Tip kx bm) stk
+    work kx bm (z:zs) stk | kx == prefixOf z = work kx (bm .|. bitmapOf z) zs stk
+    work kx bm (z:zs) stk = reduce z zs (branchMask z kx) kx (Tip kx bm) stk
+
+    reduce z zs _ px tx Nada = work (prefixOf z) (bitmapOf z) zs (Push px tx Nada)
+    reduce z zs m px tx stk@(Push py ty stk') =
+        let mxy = branchMask px py
+            pxy = mask px mxy
+        in  if shorter m mxy
+                 then reduce z zs m pxy (Bin pxy mxy ty tx) stk'
+                 else work (prefixOf z) (bitmapOf z) zs (Push px tx stk)
+
+    finish _  t  Nada = t
+    finish px tx (Push py ty stk) = finish p (link py ty px tx) stk
+        where m = branchMask px py
+              p = mask px m
+
+data Stack = Push {-# UNPACK #-} !Prefix !IntSet !Stack | Nada
+
+
+{--------------------------------------------------------------------
+  Eq
+--------------------------------------------------------------------}
+instance Eq IntSet where
+  t1 == t2  = equal t1 t2
+  t1 /= t2  = nequal t1 t2
+
+equal :: IntSet -> IntSet -> Bool
+equal (Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  = (m1 == m2) && (p1 == p2) && (equal l1 l2) && (equal r1 r2)
+equal (Tip kx1 bm1) (Tip kx2 bm2)
+  = kx1 == kx2 && bm1 == bm2
+equal Nil Nil = True
+equal _   _   = False
+
+nequal :: IntSet -> IntSet -> Bool
+nequal (Bin p1 m1 l1 r1) (Bin p2 m2 l2 r2)
+  = (m1 /= m2) || (p1 /= p2) || (nequal l1 l2) || (nequal r1 r2)
+nequal (Tip kx1 bm1) (Tip kx2 bm2)
+  = kx1 /= kx2 || bm1 /= bm2
+nequal Nil Nil = False
+nequal _   _   = True
+
+{--------------------------------------------------------------------
+  Ord
+--------------------------------------------------------------------}
+
+instance Ord IntSet where
+    compare s1 s2 = compare (toAscList s1) (toAscList s2)
+    -- tentative implementation. See if more efficient exists.
+
+{--------------------------------------------------------------------
+  Show
+--------------------------------------------------------------------}
+instance Show IntSet where
+  showsPrec p xs = showParen (p > 10) $
+    showString "fromList " . shows (toList xs)
+
+{--------------------------------------------------------------------
+  Read
+--------------------------------------------------------------------}
+instance Read IntSet where
+#ifdef __GLASGOW_HASKELL__
+  readPrec = parens $ prec 10 $ do
+    Ident "fromList" <- lexP
+    xs <- readPrec
+    return (fromList xs)
+
+  readListPrec = readListPrecDefault
+#else
+  readsPrec p = readParen (p > 10) $ \ r -> do
+    ("fromList",s) <- lex r
+    (xs,t) <- reads s
+    return (fromList xs,t)
+#endif
+
+{--------------------------------------------------------------------
+  Typeable
+--------------------------------------------------------------------}
+
+#include "Typeable.h"
+INSTANCE_TYPEABLE0(IntSet,intSetTc,"IntSet")
+
+{--------------------------------------------------------------------
+  NFData
+--------------------------------------------------------------------}
+
+-- The IntSet constructors consist only of strict fields of Ints and
+-- IntSets, thus the default NFData instance which evaluates to whnf
+-- should suffice
+instance NFData IntSet
+
+{--------------------------------------------------------------------
+  Debugging
+--------------------------------------------------------------------}
+-- | /O(n)/. Show the tree that implements the set. The tree is shown
+-- in a compressed, hanging format.
+showTree :: IntSet -> String
+showTree s
+  = showTreeWith True False s
+
+
+{- | /O(n)/. The expression (@'showTreeWith' hang wide map@) shows
+ the tree that implements the set. If @hang@ is
+ 'True', a /hanging/ tree is shown otherwise a rotated tree is shown. If
+ @wide@ is 'True', an extra wide version is shown.
+-}
+showTreeWith :: Bool -> Bool -> IntSet -> String
+showTreeWith hang wide t
+  | hang      = (showsTreeHang wide [] t) ""
+  | otherwise = (showsTree wide [] [] t) ""
+
+showsTree :: Bool -> [String] -> [String] -> IntSet -> ShowS
+showsTree wide lbars rbars t
+  = case t of
+      Bin p m l r
+          -> showsTree wide (withBar rbars) (withEmpty rbars) r .
+             showWide wide rbars .
+             showsBars lbars . showString (showBin p m) . showString "\n" .
+             showWide wide lbars .
+             showsTree wide (withEmpty lbars) (withBar lbars) l
+      Tip kx bm
+          -> showsBars lbars . showString " " . shows kx . showString " + " .
+                                                showsBitMap bm . showString "\n"
+      Nil -> showsBars lbars . showString "|\n"
+
+showsTreeHang :: Bool -> [String] -> IntSet -> ShowS
+showsTreeHang wide bars t
+  = case t of
+      Bin p m l r
+          -> showsBars bars . showString (showBin p m) . showString "\n" .
+             showWide wide bars .
+             showsTreeHang wide (withBar bars) l .
+             showWide wide bars .
+             showsTreeHang wide (withEmpty bars) r
+      Tip kx bm
+          -> showsBars bars . showString " " . shows kx . showString " + " .
+                                               showsBitMap bm . showString "\n"
+      Nil -> showsBars bars . showString "|\n"
+
+showBin :: Prefix -> Mask -> String
+showBin _ _
+  = "*" -- ++ show (p,m)
+
+showWide :: Bool -> [String] -> String -> String
+showWide wide bars
+  | wide      = showString (concat (reverse bars)) . showString "|\n"
+  | otherwise = id
+
+showsBars :: [String] -> ShowS
+showsBars bars
+  = case bars of
+      [] -> id
+      _  -> showString (concat (reverse (tail bars))) . showString node
+
+showsBitMap :: Word -> ShowS
+showsBitMap = showString . showBitMap
+
+showBitMap :: Word -> String
+showBitMap w = show $ foldrBits 0 (:) [] w
+
+node :: String
+node           = "+--"
+
+withBar, withEmpty :: [String] -> [String]
+withBar bars   = "|  ":bars
+withEmpty bars = "   ":bars
+
+
+{--------------------------------------------------------------------
+  Helpers
+--------------------------------------------------------------------}
+{--------------------------------------------------------------------
+  Link
+--------------------------------------------------------------------}
+link :: Prefix -> IntSet -> Prefix -> IntSet -> IntSet
+link p1 t1 p2 t2
+  | zero p1 m = Bin p m t1 t2
+  | otherwise = Bin p m t2 t1
+  where
+    m = branchMask p1 p2
+    p = mask p1 m
+{-# INLINE link #-}
+
+{--------------------------------------------------------------------
+  @bin@ assures that we never have empty trees within a tree.
+--------------------------------------------------------------------}
+bin :: Prefix -> Mask -> IntSet -> IntSet -> IntSet
+bin _ _ l Nil = l
+bin _ _ Nil r = r
+bin p m l r   = Bin p m l r
+{-# INLINE bin #-}
+
+{--------------------------------------------------------------------
+  @tip@ assures that we never have empty bitmaps within a tree.
+--------------------------------------------------------------------}
+tip :: Prefix -> BitMap -> IntSet
+tip _ 0 = Nil
+tip kx bm = Tip kx bm
+{-# INLINE tip #-}
+
+
+{----------------------------------------------------------------------
+  Functions that generate Prefix and BitMap of a Key or a Suffix.
+----------------------------------------------------------------------}
+
+suffixBitMask :: Int
+#if MIN_VERSION_base_4_7_0
+suffixBitMask = finiteBitSize (undefined::Word) - 1
+#else
+suffixBitMask = bitSize (undefined::Word) - 1
+#endif
+{-# INLINE suffixBitMask #-}
+
+prefixBitMask :: Int
+prefixBitMask = complement suffixBitMask
+{-# INLINE prefixBitMask #-}
+
+prefixOf :: Int -> Prefix
+prefixOf x = x .&. prefixBitMask
+{-# INLINE prefixOf #-}
+
+suffixOf :: Int -> Int
+suffixOf x = x .&. suffixBitMask
+{-# INLINE suffixOf #-}
+
+bitmapOfSuffix :: Int -> BitMap
+bitmapOfSuffix s = 1 `shiftLL` s
+{-# INLINE bitmapOfSuffix #-}
+
+bitmapOf :: Int -> BitMap
+bitmapOf x = bitmapOfSuffix (suffixOf x)
+{-# INLINE bitmapOf #-}
+
+
+{--------------------------------------------------------------------
+  Endian independent bit twiddling
+--------------------------------------------------------------------}
+zero :: Int -> Mask -> Bool
+zero i m
+  = (natFromInt i) .&. (natFromInt m) == 0
+{-# INLINE zero #-}
+
+nomatch,match :: Int -> Prefix -> Mask -> Bool
+nomatch i p m
+  = (mask i m) /= p
+{-# INLINE nomatch #-}
+
+match i p m
+  = (mask i m) == p
+{-# INLINE match #-}
+
+-- Suppose a is largest such that 2^a divides 2*m.
+-- Then mask i m is i with the low a bits zeroed out.
+mask :: Int -> Mask -> Prefix
+mask i m
+  = maskW (natFromInt i) (natFromInt m)
+{-# INLINE mask #-}
+
+{--------------------------------------------------------------------
+  Big endian operations
+--------------------------------------------------------------------}
+maskW :: Nat -> Nat -> Prefix
+maskW i m
+  = intFromNat (i .&. (complement (m-1) `xor` m))
+{-# INLINE maskW #-}
+
+shorter :: Mask -> Mask -> Bool
+shorter m1 m2
+  = (natFromInt m1) > (natFromInt m2)
+{-# INLINE shorter #-}
+
+branchMask :: Prefix -> Prefix -> Mask
+branchMask p1 p2
+  = intFromNat (highestBitMask (natFromInt p1 `xor` natFromInt p2))
+{-# INLINE branchMask #-}
+
+{----------------------------------------------------------------------
+  To get best performance, we provide fast implementations of
+  lowestBitSet, highestBitSet and fold[lr][l]Bits for GHC.
+  If the intel bsf and bsr instructions ever become GHC primops,
+  this code should be reimplemented using these.
+
+  Performance of this code is crucial for folds, toList, filter, partition.
+
+  The signatures of methods in question are placed after this comment.
+----------------------------------------------------------------------}
+
+lowestBitSet :: Nat -> Int
+highestBitSet :: Nat -> Int
+foldlBits :: Int -> (a -> Int -> a) -> a -> Nat -> a
+foldl'Bits :: Int -> (a -> Int -> a) -> a -> Nat -> a
+foldrBits :: Int -> (Int -> a -> a) -> a -> Nat -> a
+foldr'Bits :: Int -> (Int -> a -> a) -> a -> Nat -> a
+
+{-# INLINE lowestBitSet #-}
+{-# INLINE highestBitSet #-}
+{-# INLINE foldlBits #-}
+{-# INLINE foldl'Bits #-}
+{-# INLINE foldrBits #-}
+{-# INLINE foldr'Bits #-}
+
+#if defined(__GLASGOW_HASKELL__) && (WORD_SIZE_IN_BITS==32 || WORD_SIZE_IN_BITS==64)
+{----------------------------------------------------------------------
+  For lowestBitSet we use wordsize-dependant implementation based on
+  multiplication and DeBrujn indeces, which was proposed by Edward Kmett
+  <http://haskell.org/pipermail/libraries/2011-September/016749.html>
+
+  The core of this implementation is fast indexOfTheOnlyBit,
+  which is given a Nat with exactly one bit set, and returns
+  its index.
+
+  Lot of effort was put in these implementations, please benchmark carefully
+  before changing this code.
+----------------------------------------------------------------------}
+
+indexOfTheOnlyBit :: Nat -> Int
+{-# INLINE indexOfTheOnlyBit #-}
+indexOfTheOnlyBit bitmask =
+  I# (lsbArray `indexInt8OffAddr#` unboxInt (intFromNat ((bitmask * magic) `shiftRL` offset)))
+  where unboxInt (I# i) = i
+#if WORD_SIZE_IN_BITS==32
+        magic = 0x077CB531
+        offset = 27
+        !lsbArray = "\0\1\28\2\29\14\24\3\30\22\20\15\25\17\4\8\31\27\13\23\21\19\16\7\26\12\18\6\11\5\10\9"#
+#else
+        magic = 0x07EDD5E59A4E28C2
+        offset = 58
+        !lsbArray = "\63\0\58\1\59\47\53\2\60\39\48\27\54\33\42\3\61\51\37\40\49\18\28\20\55\30\34\11\43\14\22\4\62\57\46\52\38\26\32\41\50\36\17\19\29\10\13\21\56\45\25\31\35\16\9\12\44\24\15\8\23\7\6\5"#
+#endif
+-- The lsbArray gets inlined to every call site of indexOfTheOnlyBit.
+-- That cannot be easily avoided, as GHC forbids top-level Addr# literal.
+-- One could go around that by supplying getLsbArray :: () -> Addr# marked
+-- as NOINLINE. But the code size of calling it and processing the result
+-- is 48B on 32-bit and 56B on 64-bit architectures -- so the 32B and 64B array
+-- is actually improvement on 32-bit and only a 8B size increase on 64-bit.
+
+lowestBitMask :: Nat -> Nat
+lowestBitMask x = x .&. negate x
+{-# INLINE lowestBitMask #-}
+
+-- Reverse the order of bits in the Nat.
+revNat :: Nat -> Nat
+#if WORD_SIZE_IN_BITS==32
+revNat x1 = case ((x1 `shiftRL` 1) .&. 0x55555555) .|. ((x1 .&. 0x55555555) `shiftLL` 1) of
+              x2 -> case ((x2 `shiftRL` 2) .&. 0x33333333) .|. ((x2 .&. 0x33333333) `shiftLL` 2) of
+                 x3 -> case ((x3 `shiftRL` 4) .&. 0x0F0F0F0F) .|. ((x3 .&. 0x0F0F0F0F) `shiftLL` 4) of
+                   x4 -> case ((x4 `shiftRL` 8) .&. 0x00FF00FF) .|. ((x4 .&. 0x00FF00FF) `shiftLL` 8) of
+                     x5 -> ( x5 `shiftRL` 16             ) .|. ( x5               `shiftLL` 16);
+#else
+revNat x1 = case ((x1 `shiftRL` 1) .&. 0x5555555555555555) .|. ((x1 .&. 0x5555555555555555) `shiftLL` 1) of
+              x2 -> case ((x2 `shiftRL` 2) .&. 0x3333333333333333) .|. ((x2 .&. 0x3333333333333333) `shiftLL` 2) of
+                 x3 -> case ((x3 `shiftRL` 4) .&. 0x0F0F0F0F0F0F0F0F) .|. ((x3 .&. 0x0F0F0F0F0F0F0F0F) `shiftLL` 4) of
+                   x4 -> case ((x4 `shiftRL` 8) .&. 0x00FF00FF00FF00FF) .|. ((x4 .&. 0x00FF00FF00FF00FF) `shiftLL` 8) of
+                     x5 -> case ((x5 `shiftRL` 16) .&. 0x0000FFFF0000FFFF) .|. ((x5 .&. 0x0000FFFF0000FFFF) `shiftLL` 16) of
+                       x6 -> ( x6 `shiftRL` 32             ) .|. ( x6               `shiftLL` 32);
+#endif
+
+lowestBitSet x = indexOfTheOnlyBit (lowestBitMask x)
+
+highestBitSet x = indexOfTheOnlyBit (highestBitMask x)
+
+foldlBits prefix f z bitmap = go bitmap z
+  where go bm acc | bm == 0 = acc
+                  | otherwise = case lowestBitMask bm of
+                                  bitmask -> bitmask `seq` case indexOfTheOnlyBit bitmask of
+                                    bi -> bi `seq` go (bm `xor` bitmask) ((f acc) $! (prefix+bi))
+
+foldl'Bits prefix f z bitmap = go bitmap z
+  where STRICT_2_OF_2(go)
+        go bm acc | bm == 0 = acc
+                  | otherwise = case lowestBitMask bm of
+                                  bitmask -> bitmask `seq` case indexOfTheOnlyBit bitmask of
+                                    bi -> bi `seq` go (bm `xor` bitmask) ((f acc) $! (prefix+bi))
+
+foldrBits prefix f z bitmap = go (revNat bitmap) z
+  where go bm acc | bm == 0 = acc
+                  | otherwise = case lowestBitMask bm of
+                                  bitmask -> bitmask `seq` case indexOfTheOnlyBit bitmask of
+                                    bi -> bi `seq` go (bm `xor` bitmask) ((f $! (prefix+(WORD_SIZE_IN_BITS-1)-bi)) acc)
+
+foldr'Bits prefix f z bitmap = go (revNat bitmap) z
+  where STRICT_2_OF_2(go)
+        go bm acc | bm == 0 = acc
+                  | otherwise = case lowestBitMask bm of
+                                  bitmask -> bitmask `seq` case indexOfTheOnlyBit bitmask of
+                                    bi -> bi `seq` go (bm `xor` bitmask) ((f $! (prefix+(WORD_SIZE_IN_BITS-1)-bi)) acc)
+
+#else
+{----------------------------------------------------------------------
+  In general case we use logarithmic implementation of
+  lowestBitSet and highestBitSet, which works up to bit sizes of 64.
+
+  Folds are linear scans.
+----------------------------------------------------------------------}
+
+lowestBitSet n0 =
+    let (n1,b1) = if n0 .&. 0xFFFFFFFF /= 0 then (n0,0)  else (n0 `shiftRL` 32, 32)
+        (n2,b2) = if n1 .&. 0xFFFF /= 0     then (n1,b1) else (n1 `shiftRL` 16, 16+b1)
+        (n3,b3) = if n2 .&. 0xFF /= 0       then (n2,b2) else (n2 `shiftRL` 8,  8+b2)
+        (n4,b4) = if n3 .&. 0xF /= 0        then (n3,b3) else (n3 `shiftRL` 4,  4+b3)
+        (n5,b5) = if n4 .&. 0x3 /= 0        then (n4,b4) else (n4 `shiftRL` 2,  2+b4)
+        b6      = if n5 .&. 0x1 /= 0        then     b5  else                   1+b5
+    in b6
+
+highestBitSet n0 =
+    let (n1,b1) = if n0 .&. 0xFFFFFFFF00000000 /= 0 then (n0 `shiftRL` 32, 32)    else (n0,0)
+        (n2,b2) = if n1 .&. 0xFFFF0000 /= 0         then (n1 `shiftRL` 16, 16+b1) else (n1,b1)
+        (n3,b3) = if n2 .&. 0xFF00 /= 0             then (n2 `shiftRL` 8,  8+b2)  else (n2,b2)
+        (n4,b4) = if n3 .&. 0xF0 /= 0               then (n3 `shiftRL` 4,  4+b3)  else (n3,b3)
+        (n5,b5) = if n4 .&. 0xC /= 0                then (n4 `shiftRL` 2,  2+b4)  else (n4,b4)
+        b6      = if n5 .&. 0x2 /= 0                then                   1+b5   else     b5
+    in b6
+
+foldlBits prefix f z bm = let lb = lowestBitSet bm
+                          in  go (prefix+lb) z (bm `shiftRL` lb)
+  where STRICT_1_OF_3(go)
+        go _  acc 0 = acc
+        go bi acc n | n `testBit` 0 = go (bi + 1) (f acc bi) (n `shiftRL` 1)
+                    | otherwise     = go (bi + 1)    acc     (n `shiftRL` 1)
+
+foldl'Bits prefix f z bm = let lb = lowestBitSet bm
+                           in  go (prefix+lb) z (bm `shiftRL` lb)
+  where STRICT_1_OF_3(go)
+        STRICT_2_OF_3(go)
+        go _  acc 0 = acc
+        go bi acc n | n `testBit` 0 = go (bi + 1) (f acc bi) (n `shiftRL` 1)
+                    | otherwise     = go (bi + 1)    acc     (n `shiftRL` 1)
+
+foldrBits prefix f z bm = let lb = lowestBitSet bm
+                          in  go (prefix+lb) (bm `shiftRL` lb)
+  where STRICT_1_OF_2(go)
+        go _  0 = z
+        go bi n | n `testBit` 0 = f bi (go (bi + 1) (n `shiftRL` 1))
+                | otherwise     =       go (bi + 1) (n `shiftRL` 1)
+
+foldr'Bits prefix f z bm = let lb = lowestBitSet bm
+                           in  go (prefix+lb) (bm `shiftRL` lb)
+  where STRICT_1_OF_2(go)
+        go _  0 = z
+        go bi n | n `testBit` 0 = f bi $! go (bi + 1) (n `shiftRL` 1)
+                | otherwise     =         go (bi + 1) (n `shiftRL` 1)
+
+#endif
+
+{----------------------------------------------------------------------
+  [bitcount] as posted by David F. Place to haskell-cafe on April 11, 2006,
+  based on the code on
+  http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan,
+  where the following source is given:
+    Published in 1988, the C Programming Language 2nd Ed. (by Brian W.
+    Kernighan and Dennis M. Ritchie) mentions this in exercise 2-9. On April
+    19, 2006 Don Knuth pointed out to me that this method "was first published
+    by Peter Wegner in CACM 3 (1960), 322. (Also discovered independently by
+    Derrick Lehmer and published in 1964 in a book edited by Beckenbach.)"
+----------------------------------------------------------------------}
+
+bitcount :: Int -> Word -> Int
+#if MIN_VERSION_base_4_5_0
+bitcount a x = a + popCount x
+#else
+bitcount a0 x0 = go a0 x0
+  where go a 0 = a
+        go a x = go (a + 1) (x .&. (x-1))
+#endif
+{-# INLINE bitcount #-}
+
+
+{--------------------------------------------------------------------
+  Utilities
+--------------------------------------------------------------------}
+foldlStrict :: (a -> b -> a) -> a -> [b] -> a
+foldlStrict f = go
+  where
+    go z []     = z
+    go z (x:xs) = let z' = f z x in z' `seq` go z' xs
+{-# INLINE foldlStrict #-}
+
+-- | /O(1)/.  Decompose a set into pieces based on the structure of the underlying
+-- tree.  This function is useful for consuming a set in parallel.
+--
+-- No guarantee is made as to the sizes of the pieces; an internal, but
+-- deterministic process determines this.  However, it is guaranteed that the
+-- pieces returned will be in ascending order (all elements in the first submap
+-- less than all elements in the second, and so on).
+--
+-- Examples:
+--
+-- > splitRoot (fromList [1..120]) == [fromList [1..63],fromList [64..120]]
+-- > splitRoot empty == []
+--
+--  Note that the current implementation does not return more than two subsets,
+--  but you should not depend on this behaviour because it can change in the
+--  future without notice. Also, the current version does not continue
+--  splitting all the way to individual singleton sets -- it stops at some
+--  point.
+splitRoot :: IntSet -> [IntSet]
+splitRoot orig =
+  case orig of
+    Nil -> []
+    -- NOTE: we don't currently split below Tip, but we could.
+    x@(Tip _ _) -> [x]
+    Bin _ m l r | m < 0 -> [r, l]
+                | otherwise -> [l, r]
+{-# INLINE splitRoot #-}
diff --git a/Data/Map.hs b/Data/Map.hs
new file mode 100644
--- /dev/null
+++ b/Data/Map.hs
@@ -0,0 +1,129 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Safe #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Map
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- /Note:/ You should use "Data.Map.Strict" instead of this module if:
+--
+-- * You will eventually need all the values stored.
+--
+-- * The stored values don't represent large virtual data structures
+-- to be lazily computed.
+--
+-- An efficient implementation of ordered maps from keys to values
+-- (dictionaries).
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import qualified Data.Map as Map
+--
+-- The implementation of 'Map' is based on /size balanced/ binary trees (or
+-- trees of /bounded balance/) as described by:
+--
+--    * Stephen Adams, \"/Efficient sets: a balancing act/\",
+--     Journal of Functional Programming 3(4):553-562, October 1993,
+--     <http://www.swiss.ai.mit.edu/~adams/BB/>.
+--
+--    * J. Nievergelt and E.M. Reingold,
+--      \"/Binary search trees of bounded balance/\",
+--      SIAM journal of computing 2(1), March 1973.
+--
+-- Note that the implementation is /left-biased/ -- the elements of a
+-- first argument are always preferred to the second, for example in
+-- 'union' or 'insert'.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation (<http://en.wikipedia.org/wiki/Big_O_notation>).
+-----------------------------------------------------------------------------
+
+module Data.Map
+    ( module Data.Map.Lazy
+    , insertWith'
+    , insertWithKey'
+    , insertLookupWithKey'
+    , fold
+    , foldWithKey
+    ) where
+
+import Prelude hiding (foldr)
+import Data.Map.Lazy
+import qualified Data.Map.Strict as Strict
+
+-- | /Deprecated./ As of version 0.5, replaced by 'Data.Map.Strict.insertWith'.
+--
+-- /O(log n)/. Same as 'insertWith', but the value being inserted to the map is
+-- evaluated to WHNF beforehand.
+--
+-- For example, to update a counter:
+--
+-- > insertWith' (+) k 1 m
+--
+
+insertWith' :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWith' = Strict.insertWith
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertWith' #-}
+#else
+{-# INLINE insertWith' #-}
+#endif
+
+-- | /Deprecated./ As of version 0.5, replaced by
+-- 'Data.Map.Strict.insertWithKey'.
+--
+-- /O(log n)/. Same as 'insertWithKey', but the value being inserted to the map is
+-- evaluated to WHNF beforehand.
+
+insertWithKey' :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+-- We do not reuse Data.Map.Strict.insertWithKey, because it is stricter -- it
+-- forces evaluation of the given value.
+insertWithKey' = Strict.insertWithKey
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertWithKey' #-}
+#else
+{-# INLINE insertWithKey' #-}
+#endif
+
+-- | /Deprecated./ As of version 0.5, replaced by
+-- 'Data.Map.Strict.insertLookupWithKey'.
+--
+-- /O(log n)/. Same as 'insertLookupWithKey', but the value being inserted to
+-- the map is evaluated to WHNF beforehand.
+
+insertLookupWithKey' :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a
+                     -> (Maybe a, Map k a)
+-- We do not reuse Data.Map.Strict.insertLookupWithKey, because it is stricter -- it
+-- forces evaluation of the given value.
+insertLookupWithKey' = Strict.insertLookupWithKey
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertLookupWithKey' #-}
+#else
+{-# INLINE insertLookupWithKey' #-}
+#endif
+
+-- | /Deprecated./ As of version 0.5, replaced by 'foldr'.
+--
+-- /O(n)/. Fold the values in the map using the given right-associative
+-- binary operator. This function is an equivalent of 'foldr' and is present
+-- for compatibility only.
+fold :: (a -> b -> b) -> b -> Map k a -> b
+fold = foldr
+{-# INLINE fold #-}
+
+-- | /Deprecated./ As of version 0.4, replaced by 'foldrWithKey'.
+--
+-- /O(n)/. Fold the keys and values in the map using the given right-associative
+-- binary operator. This function is an equivalent of 'foldrWithKey' and is present
+-- for compatibility only.
+foldWithKey :: (k -> a -> b -> b) -> b -> Map k a -> b
+foldWithKey = foldrWithKey
+{-# INLINE foldWithKey #-}
diff --git a/Data/Map/Base.hs b/Data/Map/Base.hs
new file mode 100644
--- /dev/null
+++ b/Data/Map/Base.hs
@@ -0,0 +1,2868 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE DeriveDataTypeable, StandaloneDeriving #-}
+#endif
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE RoleAnnotations #-}
+{-# LANGUAGE TypeFamilies #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Map.Base
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of maps from keys to values (dictionaries).
+--
+-- Since many function names (but not the type name) clash with
+-- "Prelude" names, this module is usually imported @qualified@, e.g.
+--
+-- >  import Data.Map (Map)
+-- >  import qualified Data.Map as Map
+--
+-- The implementation of 'Map' is based on /size balanced/ binary trees (or
+-- trees of /bounded balance/) as described by:
+--
+--    * Stephen Adams, \"/Efficient sets: a balancing act/\",
+--     Journal of Functional Programming 3(4):553-562, October 1993,
+--     <http://www.swiss.ai.mit.edu/~adams/BB/>.
+--
+--    * J. Nievergelt and E.M. Reingold,
+--      \"/Binary search trees of bounded balance/\",
+--      SIAM journal of computing 2(1), March 1973.
+--
+-- Note that the implementation is /left-biased/ -- the elements of a
+-- first argument are always preferred to the second, for example in
+-- 'union' or 'insert'.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation <http://en.wikipedia.org/wiki/Big_O_notation>.
+-----------------------------------------------------------------------------
+
+-- [Note: Using INLINABLE]
+-- ~~~~~~~~~~~~~~~~~~~~~~~
+-- It is crucial to the performance that the functions specialize on the Ord
+-- type when possible. GHC 7.0 and higher does this by itself when it sees th
+-- unfolding of a function -- that is why all public functions are marked
+-- INLINABLE (that exposes the unfolding).
+
+
+-- [Note: Using INLINE]
+-- ~~~~~~~~~~~~~~~~~~~~
+-- For other compilers and GHC pre 7.0, we mark some of the functions INLINE.
+-- We mark the functions that just navigate down the tree (lookup, insert,
+-- delete and similar). That navigation code gets inlined and thus specialized
+-- when possible. There is a price to pay -- code growth. The code INLINED is
+-- therefore only the tree navigation, all the real work (rebalancing) is not
+-- INLINED by using a NOINLINE.
+--
+-- All methods marked INLINE have to be nonrecursive -- a 'go' function doing
+-- the real work is provided.
+
+
+-- [Note: Type of local 'go' function]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- If the local 'go' function uses an Ord class, it sometimes heap-allocates
+-- the Ord dictionary when the 'go' function does not have explicit type.
+-- In that case we give 'go' explicit type. But this slightly decrease
+-- performance, as the resulting 'go' function can float out to top level.
+
+
+-- [Note: Local 'go' functions and capturing]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- As opposed to IntMap, when 'go' function captures an argument, increased
+-- heap-allocation can occur: sometimes in a polymorphic function, the 'go'
+-- floats out of its enclosing function and then it heap-allocates the
+-- dictionary and the argument. Maybe it floats out too late and strictness
+-- analyzer cannot see that these could be passed on stack.
+--
+-- For example, change 'member' so that its local 'go' function is not passing
+-- argument k and then look at the resulting code for hedgeInt.
+
+
+-- [Note: Order of constructors]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- The order of constructors of Map matters when considering performance.
+-- Currently in GHC 7.0, when type has 2 constructors, a forward conditional
+-- jump is made when successfully matching second constructor. Successful match
+-- of first constructor results in the forward jump not taken.
+-- On GHC 7.0, reordering constructors from Tip | Bin to Bin | Tip
+-- improves the benchmark by up to 10% on x86.
+
+module Data.Map.Base (
+    -- * Map type
+      Map(..)          -- instance Eq,Show,Read
+
+    -- * Operators
+    , (!), (\\)
+
+    -- * Query
+    , null
+    , size
+    , member
+    , notMember
+    , lookup
+    , findWithDefault
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+
+    -- * Construction
+    , empty
+    , singleton
+
+    -- ** Insertion
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+
+    -- ** Delete\/Update
+    , delete
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+
+    -- * Combine
+
+    -- ** Union
+    , union
+    , unionWith
+    , unionWithKey
+    , unions
+    , unionsWith
+
+    -- ** Difference
+    , difference
+    , differenceWith
+    , differenceWithKey
+
+    -- ** Intersection
+    , intersection
+    , intersectionWith
+    , intersectionWithKey
+
+    -- ** Universal combining function
+    , mergeWithKey
+
+    -- * Traversal
+    -- ** Map
+    , map
+    , mapWithKey
+    , traverseWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeys
+    , mapKeysWith
+    , mapKeysMonotonic
+
+    -- * Folds
+    , foldr
+    , foldl
+    , foldrWithKey
+    , foldlWithKey
+    , foldMapWithKey
+
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    , foldrWithKey'
+    , foldlWithKey'
+
+    -- * Conversion
+    , elems
+    , keys
+    , assocs
+    , keysSet
+    , fromSet
+
+    -- ** Lists
+    , toList
+    , fromList
+    , fromListWith
+    , fromListWithKey
+
+    -- ** Ordered lists
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+
+    -- * Filter
+    , filter
+    , filterWithKey
+    , partition
+    , partitionWithKey
+
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+
+    , split
+    , splitLookup
+    , splitRoot
+
+    -- * Submap
+    , isSubmapOf, isSubmapOfBy
+    , isProperSubmapOf, isProperSubmapOfBy
+
+    -- * Indexed
+    , lookupIndex
+    , findIndex
+    , elemAt
+    , updateAt
+    , deleteAt
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    , minView
+    , maxView
+    , minViewWithKey
+    , maxViewWithKey
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+    , valid
+
+    -- Used by the strict version
+    , bin
+    , balance
+    , balanced
+    , balanceL
+    , balanceR
+    , delta
+    , link
+    , insertMax
+    , merge
+    , glue
+    , trim
+    , trimLookupLo
+    , foldlStrict
+    , MaybeS(..)
+    , filterGt
+    , filterLt
+    ) where
+
+import Control.Applicative (Applicative(..), (<$>))
+import Control.DeepSeq (NFData(rnf))
+import Data.Bits (shiftL, shiftR)
+import qualified Data.Foldable as Foldable
+import Data.Monoid (Monoid(..))
+import Data.StrictPair
+import Data.Traversable (Traversable(traverse))
+import Data.Typeable
+import Prelude hiding (lookup, map, filter, foldr, foldl, null)
+
+import qualified Data.Set.Base as Set
+
+#if __GLASGOW_HASKELL__
+import GHC.Exts ( build )
+#if __GLASGOW_HASKELL__ >= 708
+import qualified GHC.Exts as GHCExts
+#endif
+import Text.Read
+import Data.Data
+#endif
+
+-- Use macros to define strictness of functions.
+-- STRICT_x_OF_y denotes an y-ary function strict in the x-th parameter.
+-- We do not use BangPatterns, because they are not in any standard and we
+-- want the compilers to be compiled by as many compilers as possible.
+#define STRICT_1_OF_2(fn) fn arg _ | arg `seq` False = undefined
+#define STRICT_1_OF_3(fn) fn arg _ _ | arg `seq` False = undefined
+#define STRICT_2_OF_3(fn) fn _ arg _ | arg `seq` False = undefined
+#define STRICT_1_OF_4(fn) fn arg _ _ _ | arg `seq` False = undefined
+#define STRICT_2_OF_4(fn) fn _ arg _ _ | arg `seq` False = undefined
+
+{--------------------------------------------------------------------
+  Operators
+--------------------------------------------------------------------}
+infixl 9 !,\\ --
+
+-- | /O(log n)/. Find the value at a key.
+-- Calls 'error' when the element can not be found.
+--
+-- > fromList [(5,'a'), (3,'b')] ! 1    Error: element not in the map
+-- > fromList [(5,'a'), (3,'b')] ! 5 == 'a'
+
+(!) :: Ord k => Map k a -> k -> a
+m ! k = find k m
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE (!) #-}
+#endif
+
+-- | Same as 'difference'.
+(\\) :: Ord k => Map k a -> Map k b -> Map k a
+m1 \\ m2 = difference m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE (\\) #-}
+#endif
+
+{--------------------------------------------------------------------
+  Size balanced trees.
+--------------------------------------------------------------------}
+-- | A Map from keys @k@ to values @a@.
+
+-- See Note: Order of constructors
+data Map k a  = Bin {-# UNPACK #-} !Size !k a !(Map k a) !(Map k a)
+              | Tip
+
+type Size     = Int
+
+#if __GLASGOW_HASKELL__ >= 708
+type role Map nominal representational
+#endif
+
+instance (Ord k) => Monoid (Map k v) where
+    mempty  = empty
+    mappend = union
+    mconcat = unions
+
+#if __GLASGOW_HASKELL__
+
+{--------------------------------------------------------------------
+  A Data instance
+--------------------------------------------------------------------}
+
+-- This instance preserves data abstraction at the cost of inefficiency.
+-- We provide limited reflection services for the sake of data abstraction.
+
+instance (Data k, Data a, Ord k) => Data (Map k a) where
+  gfoldl f z m   = z fromList `f` toList m
+  toConstr _     = fromListConstr
+  gunfold k z c  = case constrIndex c of
+    1 -> k (z fromList)
+    _ -> error "gunfold"
+  dataTypeOf _   = mapDataType
+  dataCast2 f    = gcast2 f
+
+fromListConstr :: Constr
+fromListConstr = mkConstr mapDataType "fromList" [] Prefix
+
+mapDataType :: DataType
+mapDataType = mkDataType "Data.Map.Base.Map" [fromListConstr]
+
+#endif
+
+{--------------------------------------------------------------------
+  Query
+--------------------------------------------------------------------}
+-- | /O(1)/. Is the map empty?
+--
+-- > Data.Map.null (empty)           == True
+-- > Data.Map.null (singleton 1 'a') == False
+
+null :: Map k a -> Bool
+null Tip      = True
+null (Bin {}) = False
+{-# INLINE null #-}
+
+-- | /O(1)/. The number of elements in the map.
+--
+-- > size empty                                   == 0
+-- > size (singleton 1 'a')                       == 1
+-- > size (fromList([(1,'a'), (2,'c'), (3,'b')])) == 3
+
+size :: Map k a -> Int
+size Tip              = 0
+size (Bin sz _ _ _ _) = sz
+{-# INLINE size #-}
+
+
+-- | /O(log n)/. Lookup the value at a key in the map.
+--
+-- The function will return the corresponding value as @('Just' value)@,
+-- or 'Nothing' if the key isn't in the map.
+--
+-- An example of using @lookup@:
+--
+-- > import Prelude hiding (lookup)
+-- > import Data.Map
+-- >
+-- > employeeDept = fromList([("John","Sales"), ("Bob","IT")])
+-- > deptCountry = fromList([("IT","USA"), ("Sales","France")])
+-- > countryCurrency = fromList([("USA", "Dollar"), ("France", "Euro")])
+-- >
+-- > employeeCurrency :: String -> Maybe String
+-- > employeeCurrency name = do
+-- >     dept <- lookup name employeeDept
+-- >     country <- lookup dept deptCountry
+-- >     lookup country countryCurrency
+-- >
+-- > main = do
+-- >     putStrLn $ "John's currency: " ++ (show (employeeCurrency "John"))
+-- >     putStrLn $ "Pete's currency: " ++ (show (employeeCurrency "Pete"))
+--
+-- The output of this program:
+--
+-- >   John's currency: Just "Euro"
+-- >   Pete's currency: Nothing
+lookup :: Ord k => k -> Map k a -> Maybe a
+lookup = go
+  where
+    STRICT_1_OF_2(go)
+    go _ Tip = Nothing
+    go k (Bin _ kx x l r) = case compare k kx of
+      LT -> go k l
+      GT -> go k r
+      EQ -> Just x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookup #-}
+#else
+{-# INLINE lookup #-}
+#endif
+
+-- | /O(log n)/. Is the key a member of the map? See also 'notMember'.
+--
+-- > member 5 (fromList [(5,'a'), (3,'b')]) == True
+-- > member 1 (fromList [(5,'a'), (3,'b')]) == False
+member :: Ord k => k -> Map k a -> Bool
+member = go
+  where
+    STRICT_1_OF_2(go)
+    go _ Tip = False
+    go k (Bin _ kx _ l r) = case compare k kx of
+      LT -> go k l
+      GT -> go k r
+      EQ -> True
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE member #-}
+#else
+{-# INLINE member #-}
+#endif
+
+infix 4 `member`
+
+-- | /O(log n)/. Is the key not a member of the map? See also 'member'.
+--
+-- > notMember 5 (fromList [(5,'a'), (3,'b')]) == False
+-- > notMember 1 (fromList [(5,'a'), (3,'b')]) == True
+
+notMember :: Ord k => k -> Map k a -> Bool
+notMember k m = not $ member k m
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE notMember #-}
+#else
+{-# INLINE notMember #-}
+#endif
+
+infix 4 `notMember`
+
+-- | /O(log n)/. Find the value at a key.
+-- Calls 'error' when the element can not be found.
+find :: Ord k => k -> Map k a -> a
+find = go
+  where
+    STRICT_1_OF_2(go)
+    go _ Tip = error "Map.!: given key is not an element in the map"
+    go k (Bin _ kx x l r) = case compare k kx of
+      LT -> go k l
+      GT -> go k r
+      EQ -> x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE find #-}
+#else
+{-# INLINE find #-}
+#endif
+
+-- | /O(log n)/. The expression @('findWithDefault' def k map)@ returns
+-- the value at key @k@ or returns default value @def@
+-- when the key is not in the map.
+--
+-- > findWithDefault 'x' 1 (fromList [(5,'a'), (3,'b')]) == 'x'
+-- > findWithDefault 'x' 5 (fromList [(5,'a'), (3,'b')]) == 'a'
+findWithDefault :: Ord k => a -> k -> Map k a -> a
+findWithDefault = go
+  where
+    STRICT_2_OF_3(go)
+    go def _ Tip = def
+    go def k (Bin _ kx x l r) = case compare k kx of
+      LT -> go def k l
+      GT -> go def k r
+      EQ -> x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE findWithDefault #-}
+#else
+{-# INLINE findWithDefault #-}
+#endif
+
+-- | /O(log n)/. Find largest key smaller than the given one and return the
+-- corresponding (key, value) pair.
+--
+-- > lookupLT 3 (fromList [(3,'a'), (5,'b')]) == Nothing
+-- > lookupLT 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
+lookupLT :: Ord k => k -> Map k v -> Maybe (k, v)
+lookupLT = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing k (Bin _ kx x l r) | k <= kx = goNothing k l
+                                 | otherwise = goJust k kx x r
+
+    STRICT_1_OF_4(goJust)
+    goJust _ kx' x' Tip = Just (kx', x')
+    goJust k kx' x' (Bin _ kx x l r) | k <= kx = goJust k kx' x' l
+                                     | otherwise = goJust k kx x r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupLT #-}
+#else
+{-# INLINE lookupLT #-}
+#endif
+
+-- | /O(log n)/. Find smallest key greater than the given one and return the
+-- corresponding (key, value) pair.
+--
+-- > lookupGT 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
+-- > lookupGT 5 (fromList [(3,'a'), (5,'b')]) == Nothing
+lookupGT :: Ord k => k -> Map k v -> Maybe (k, v)
+lookupGT = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing k (Bin _ kx x l r) | k < kx = goJust k kx x l
+                                 | otherwise = goNothing k r
+
+    STRICT_1_OF_4(goJust)
+    goJust _ kx' x' Tip = Just (kx', x')
+    goJust k kx' x' (Bin _ kx x l r) | k < kx = goJust k kx x l
+                                     | otherwise = goJust k kx' x' r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupGT #-}
+#else
+{-# INLINE lookupGT #-}
+#endif
+
+-- | /O(log n)/. Find largest key smaller or equal to the given one and return
+-- the corresponding (key, value) pair.
+--
+-- > lookupLE 2 (fromList [(3,'a'), (5,'b')]) == Nothing
+-- > lookupLE 4 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
+-- > lookupLE 5 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
+lookupLE :: Ord k => k -> Map k v -> Maybe (k, v)
+lookupLE = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing k (Bin _ kx x l r) = case compare k kx of LT -> goNothing k l
+                                                        EQ -> Just (kx, x)
+                                                        GT -> goJust k kx x r
+
+    STRICT_1_OF_4(goJust)
+    goJust _ kx' x' Tip = Just (kx', x')
+    goJust k kx' x' (Bin _ kx x l r) = case compare k kx of LT -> goJust k kx' x' l
+                                                            EQ -> Just (kx, x)
+                                                            GT -> goJust k kx x r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupLE #-}
+#else
+{-# INLINE lookupLE #-}
+#endif
+
+-- | /O(log n)/. Find smallest key greater or equal to the given one and return
+-- the corresponding (key, value) pair.
+--
+-- > lookupGE 3 (fromList [(3,'a'), (5,'b')]) == Just (3, 'a')
+-- > lookupGE 4 (fromList [(3,'a'), (5,'b')]) == Just (5, 'b')
+-- > lookupGE 6 (fromList [(3,'a'), (5,'b')]) == Nothing
+lookupGE :: Ord k => k -> Map k v -> Maybe (k, v)
+lookupGE = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing k (Bin _ kx x l r) = case compare k kx of LT -> goJust k kx x l
+                                                        EQ -> Just (kx, x)
+                                                        GT -> goNothing k r
+
+    STRICT_1_OF_4(goJust)
+    goJust _ kx' x' Tip = Just (kx', x')
+    goJust k kx' x' (Bin _ kx x l r) = case compare k kx of LT -> goJust k kx x l
+                                                            EQ -> Just (kx, x)
+                                                            GT -> goJust k kx' x' r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupGE #-}
+#else
+{-# INLINE lookupGE #-}
+#endif
+
+{--------------------------------------------------------------------
+  Construction
+--------------------------------------------------------------------}
+-- | /O(1)/. The empty map.
+--
+-- > empty      == fromList []
+-- > size empty == 0
+
+empty :: Map k a
+empty = Tip
+{-# INLINE empty #-}
+
+-- | /O(1)/. A map with a single element.
+--
+-- > singleton 1 'a'        == fromList [(1, 'a')]
+-- > size (singleton 1 'a') == 1
+
+singleton :: k -> a -> Map k a
+singleton k x = Bin 1 k x Tip Tip
+{-# INLINE singleton #-}
+
+{--------------------------------------------------------------------
+  Insertion
+--------------------------------------------------------------------}
+-- | /O(log n)/. Insert a new key and value in the map.
+-- If the key is already present in the map, the associated value is
+-- replaced with the supplied value. 'insert' is equivalent to
+-- @'insertWith' 'const'@.
+--
+-- > insert 5 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'x')]
+-- > insert 7 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+-- > insert 5 'x' empty                         == singleton 5 'x'
+
+-- See Note: Type of local 'go' function
+insert :: Ord k => k -> a -> Map k a -> Map k a
+insert = go
+  where
+    go :: Ord k => k -> a -> Map k a -> Map k a
+    STRICT_1_OF_3(go)
+    go kx x Tip = singleton kx x
+    go kx x (Bin sz ky y l r) =
+        case compare kx ky of
+            LT -> balanceL ky y (go kx x l) r
+            GT -> balanceR ky y l (go kx x r)
+            EQ -> Bin sz kx x l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insert #-}
+#else
+{-# INLINE insert #-}
+#endif
+
+-- Insert a new key and value in the map if it is not already present.
+-- Used by `union`.
+
+-- See Note: Type of local 'go' function
+insertR :: Ord k => k -> a -> Map k a -> Map k a
+insertR = go
+  where
+    go :: Ord k => k -> a -> Map k a -> Map k a
+    STRICT_1_OF_3(go)
+    go kx x Tip = singleton kx x
+    go kx x t@(Bin _ ky y l r) =
+        case compare kx ky of
+            LT -> balanceL ky y (go kx x l) r
+            GT -> balanceR ky y l (go kx x r)
+            EQ -> t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertR #-}
+#else
+{-# INLINE insertR #-}
+#endif
+
+-- | /O(log n)/. Insert with a function, combining new value and old value.
+-- @'insertWith' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert the pair @(key, f new_value old_value)@.
+--
+-- > insertWith (++) 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "xxxa")]
+-- > insertWith (++) 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWith (++) 5 "xxx" empty                         == singleton 5 "xxx"
+
+insertWith :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWith f = insertWithKey (\_ x' y' -> f x' y')
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertWith #-}
+#else
+{-# INLINE insertWith #-}
+#endif
+
+-- | /O(log n)/. Insert with a function, combining key, new value and old value.
+-- @'insertWithKey' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert the pair @(key,f key new_value old_value)@.
+-- Note that the key passed to f is the same key passed to 'insertWithKey'.
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:xxx|a")]
+-- > insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWithKey f 5 "xxx" empty                         == singleton 5 "xxx"
+
+-- See Note: Type of local 'go' function
+insertWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWithKey = go
+  where
+    go :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+    STRICT_2_OF_4(go)
+    go _ kx x Tip = singleton kx x
+    go f kx x (Bin sy ky y l r) =
+        case compare kx ky of
+            LT -> balanceL ky y (go f kx x l) r
+            GT -> balanceR ky y l (go f kx x r)
+            EQ -> Bin sy kx (f kx x y) l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertWithKey #-}
+#else
+{-# INLINE insertWithKey #-}
+#endif
+
+-- | /O(log n)/. Combines insert operation with old value retrieval.
+-- The expression (@'insertLookupWithKey' f k x map@)
+-- is a pair where the first element is equal to (@'lookup' k map@)
+-- and the second element equal to (@'insertWithKey' f k x map@).
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:xxx|a")])
+-- > insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "xxx")])
+-- > insertLookupWithKey f 5 "xxx" empty                         == (Nothing,  singleton 5 "xxx")
+--
+-- This is how to define @insertLookup@ using @insertLookupWithKey@:
+--
+-- > let insertLookup kx x t = insertLookupWithKey (\_ a _ -> a) kx x t
+-- > insertLookup 5 "x" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "x")])
+-- > insertLookup 7 "x" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "x")])
+
+-- See Note: Type of local 'go' function
+insertLookupWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a
+                    -> (Maybe a, Map k a)
+insertLookupWithKey = go
+  where
+    go :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> (Maybe a, Map k a)
+    STRICT_2_OF_4(go)
+    go _ kx x Tip = (Nothing, singleton kx x)
+    go f kx x (Bin sy ky y l r) =
+        case compare kx ky of
+            LT -> let (found, l') = go f kx x l
+                  in (found, balanceL ky y l' r)
+            GT -> let (found, r') = go f kx x r
+                  in (found, balanceR ky y l r')
+            EQ -> (Just y, Bin sy kx (f kx x y) l r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertLookupWithKey #-}
+#else
+{-# INLINE insertLookupWithKey #-}
+#endif
+
+{--------------------------------------------------------------------
+  Deletion
+--------------------------------------------------------------------}
+-- | /O(log n)/. Delete a key and its value from the map. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > delete 5 (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > delete 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > delete 5 empty                         == empty
+
+-- See Note: Type of local 'go' function
+delete :: Ord k => k -> Map k a -> Map k a
+delete = go
+  where
+    go :: Ord k => k -> Map k a -> Map k a
+    STRICT_1_OF_2(go)
+    go _ Tip = Tip
+    go k (Bin _ kx x l r) =
+        case compare k kx of
+            LT -> balanceR kx x (go k l) r
+            GT -> balanceL kx x l (go k r)
+            EQ -> glue l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE delete #-}
+#else
+{-# INLINE delete #-}
+#endif
+
+-- | /O(log n)/. Update a value at a specific key with the result of the provided function.
+-- When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjust ("new " ++) 7 empty                         == empty
+
+adjust :: Ord k => (a -> a) -> k -> Map k a -> Map k a
+adjust f = adjustWithKey (\_ x -> f x)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE adjust #-}
+#else
+{-# INLINE adjust #-}
+#endif
+
+-- | /O(log n)/. Adjust a value at a specific key. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > let f key x = (show key) ++ ":new " ++ x
+-- > adjustWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > adjustWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjustWithKey f 7 empty                         == empty
+
+adjustWithKey :: Ord k => (k -> a -> a) -> k -> Map k a -> Map k a
+adjustWithKey f = updateWithKey (\k' x' -> Just (f k' x'))
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE adjustWithKey #-}
+#else
+{-# INLINE adjustWithKey #-}
+#endif
+
+-- | /O(log n)/. The expression (@'update' f k map@) updates the value @x@
+-- at @k@ (if it is in the map). If (@f x@) is 'Nothing', the element is
+-- deleted. If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > update f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > update f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > update f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+update :: Ord k => (a -> Maybe a) -> k -> Map k a -> Map k a
+update f = updateWithKey (\_ x -> f x)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE update #-}
+#else
+{-# INLINE update #-}
+#endif
+
+-- | /O(log n)/. The expression (@'updateWithKey' f k map@) updates the
+-- value @x@ at @k@ (if it is in the map). If (@f k x@) is 'Nothing',
+-- the element is deleted. If it is (@'Just' y@), the key @k@ is bound
+-- to the new value @y@.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > updateWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > updateWithKey f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+-- See Note: Type of local 'go' function
+updateWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> Map k a
+updateWithKey = go
+  where
+    go :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> Map k a
+    STRICT_2_OF_3(go)
+    go _ _ Tip = Tip
+    go f k(Bin sx kx x l r) =
+        case compare k kx of
+           LT -> balanceR kx x (go f k l) r
+           GT -> balanceL kx x l (go f k r)
+           EQ -> case f kx x of
+                   Just x' -> Bin sx kx x' l r
+                   Nothing -> glue l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE updateWithKey #-}
+#else
+{-# INLINE updateWithKey #-}
+#endif
+
+-- | /O(log n)/. Lookup and update. See also 'updateWithKey'.
+-- The function returns changed value, if it is updated.
+-- Returns the original key value if the map entry is deleted.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateLookupWithKey f 5 (fromList [(5,"a"), (3,"b")]) == (Just "5:new a", fromList [(3, "b"), (5, "5:new a")])
+-- > updateLookupWithKey f 7 (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a")])
+-- > updateLookupWithKey f 3 (fromList [(5,"a"), (3,"b")]) == (Just "b", singleton 5 "a")
+
+-- See Note: Type of local 'go' function
+updateLookupWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> (Maybe a,Map k a)
+updateLookupWithKey = go
+ where
+   go :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> (Maybe a,Map k a)
+   STRICT_2_OF_3(go)
+   go _ _ Tip = (Nothing,Tip)
+   go f k (Bin sx kx x l r) =
+          case compare k kx of
+               LT -> let (found,l') = go f k l in (found,balanceR kx x l' r)
+               GT -> let (found,r') = go f k r in (found,balanceL kx x l r')
+               EQ -> case f kx x of
+                       Just x' -> (Just x',Bin sx kx x' l r)
+                       Nothing -> (Just x,glue l r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE updateLookupWithKey #-}
+#else
+{-# INLINE updateLookupWithKey #-}
+#endif
+
+-- | /O(log n)/. The expression (@'alter' f k map@) alters the value @x@ at @k@, or absence thereof.
+-- 'alter' can be used to insert, delete, or update a value in a 'Map'.
+-- In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.
+--
+-- > let f _ = Nothing
+-- > alter f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > alter f 5 (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- >
+-- > let f _ = Just "c"
+-- > alter f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "c")]
+-- > alter f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "c")]
+
+-- See Note: Type of local 'go' function
+alter :: Ord k => (Maybe a -> Maybe a) -> k -> Map k a -> Map k a
+alter = go
+  where
+    go :: Ord k => (Maybe a -> Maybe a) -> k -> Map k a -> Map k a
+    STRICT_2_OF_3(go)
+    go f k Tip = case f Nothing of
+               Nothing -> Tip
+               Just x  -> singleton k x
+
+    go f k (Bin sx kx x l r) = case compare k kx of
+               LT -> balance kx x (go f k l) r
+               GT -> balance kx x l (go f k r)
+               EQ -> case f (Just x) of
+                       Just x' -> Bin sx kx x' l r
+                       Nothing -> glue l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE alter #-}
+#else
+{-# INLINE alter #-}
+#endif
+
+{--------------------------------------------------------------------
+  Indexing
+--------------------------------------------------------------------}
+-- | /O(log n)/. Return the /index/ of a key, which is its zero-based index in
+-- the sequence sorted by keys. The index is a number from /0/ up to, but not
+-- including, the 'size' of the map. Calls 'error' when the key is not
+-- a 'member' of the map.
+--
+-- > findIndex 2 (fromList [(5,"a"), (3,"b")])    Error: element is not in the map
+-- > findIndex 3 (fromList [(5,"a"), (3,"b")]) == 0
+-- > findIndex 5 (fromList [(5,"a"), (3,"b")]) == 1
+-- > findIndex 6 (fromList [(5,"a"), (3,"b")])    Error: element is not in the map
+
+-- See Note: Type of local 'go' function
+findIndex :: Ord k => k -> Map k a -> Int
+findIndex = go 0
+  where
+    go :: Ord k => Int -> k -> Map k a -> Int
+    STRICT_1_OF_3(go)
+    STRICT_2_OF_3(go)
+    go _   _ Tip  = error "Map.findIndex: element is not in the map"
+    go idx k (Bin _ kx _ l r) = case compare k kx of
+      LT -> go idx k l
+      GT -> go (idx + size l + 1) k r
+      EQ -> idx + size l
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE findIndex #-}
+#endif
+
+-- | /O(log n)/. Lookup the /index/ of a key, which is its zero-based index in
+-- the sequence sorted by keys. The index is a number from /0/ up to, but not
+-- including, the 'size' of the map.
+--
+-- > isJust (lookupIndex 2 (fromList [(5,"a"), (3,"b")]))   == False
+-- > fromJust (lookupIndex 3 (fromList [(5,"a"), (3,"b")])) == 0
+-- > fromJust (lookupIndex 5 (fromList [(5,"a"), (3,"b")])) == 1
+-- > isJust (lookupIndex 6 (fromList [(5,"a"), (3,"b")]))   == False
+
+-- See Note: Type of local 'go' function
+lookupIndex :: Ord k => k -> Map k a -> Maybe Int
+lookupIndex = go 0
+  where
+    go :: Ord k => Int -> k -> Map k a -> Maybe Int
+    STRICT_1_OF_3(go)
+    STRICT_2_OF_3(go)
+    go _   _ Tip  = Nothing
+    go idx k (Bin _ kx _ l r) = case compare k kx of
+      LT -> go idx k l
+      GT -> go (idx + size l + 1) k r
+      EQ -> Just $! idx + size l
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupIndex #-}
+#endif
+
+-- | /O(log n)/. Retrieve an element by its /index/, i.e. by its zero-based
+-- index in the sequence sorted by keys. If the /index/ is out of range (less
+-- than zero, greater or equal to 'size' of the map), 'error' is called.
+--
+-- > elemAt 0 (fromList [(5,"a"), (3,"b")]) == (3,"b")
+-- > elemAt 1 (fromList [(5,"a"), (3,"b")]) == (5, "a")
+-- > elemAt 2 (fromList [(5,"a"), (3,"b")])    Error: index out of range
+
+elemAt :: Int -> Map k a -> (k,a)
+STRICT_1_OF_2(elemAt)
+elemAt _ Tip = error "Map.elemAt: index out of range"
+elemAt i (Bin _ kx x l r)
+  = case compare i sizeL of
+      LT -> elemAt i l
+      GT -> elemAt (i-sizeL-1) r
+      EQ -> (kx,x)
+  where
+    sizeL = size l
+
+-- | /O(log n)/. Update the element at /index/, i.e. by its zero-based index in
+-- the sequence sorted by keys. If the /index/ is out of range (less than zero,
+-- greater or equal to 'size' of the map), 'error' is called.
+--
+-- > updateAt (\ _ _ -> Just "x") 0    (fromList [(5,"a"), (3,"b")]) == fromList [(3, "x"), (5, "a")]
+-- > updateAt (\ _ _ -> Just "x") 1    (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "x")]
+-- > updateAt (\ _ _ -> Just "x") 2    (fromList [(5,"a"), (3,"b")])    Error: index out of range
+-- > updateAt (\ _ _ -> Just "x") (-1) (fromList [(5,"a"), (3,"b")])    Error: index out of range
+-- > updateAt (\_ _  -> Nothing)  0    (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+-- > updateAt (\_ _  -> Nothing)  1    (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > updateAt (\_ _  -> Nothing)  2    (fromList [(5,"a"), (3,"b")])    Error: index out of range
+-- > updateAt (\_ _  -> Nothing)  (-1) (fromList [(5,"a"), (3,"b")])    Error: index out of range
+
+updateAt :: (k -> a -> Maybe a) -> Int -> Map k a -> Map k a
+updateAt f i t = i `seq`
+  case t of
+    Tip -> error "Map.updateAt: index out of range"
+    Bin sx kx x l r -> case compare i sizeL of
+      LT -> balanceR kx x (updateAt f i l) r
+      GT -> balanceL kx x l (updateAt f (i-sizeL-1) r)
+      EQ -> case f kx x of
+              Just x' -> Bin sx kx x' l r
+              Nothing -> glue l r
+      where
+        sizeL = size l
+
+-- | /O(log n)/. Delete the element at /index/, i.e. by its zero-based index in
+-- the sequence sorted by keys. If the /index/ is out of range (less than zero,
+-- greater or equal to 'size' of the map), 'error' is called.
+--
+-- > deleteAt 0  (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+-- > deleteAt 1  (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > deleteAt 2 (fromList [(5,"a"), (3,"b")])     Error: index out of range
+-- > deleteAt (-1) (fromList [(5,"a"), (3,"b")])  Error: index out of range
+
+deleteAt :: Int -> Map k a -> Map k a
+deleteAt i t = i `seq`
+  case t of
+    Tip -> error "Map.deleteAt: index out of range"
+    Bin _ kx x l r -> case compare i sizeL of
+      LT -> balanceR kx x (deleteAt i l) r
+      GT -> balanceL kx x l (deleteAt (i-sizeL-1) r)
+      EQ -> glue l r
+      where
+        sizeL = size l
+
+
+{--------------------------------------------------------------------
+  Minimal, Maximal
+--------------------------------------------------------------------}
+-- | /O(log n)/. The minimal key of the map. Calls 'error' if the map is empty.
+--
+-- > findMin (fromList [(5,"a"), (3,"b")]) == (3,"b")
+-- > findMin empty                            Error: empty map has no minimal element
+
+findMin :: Map k a -> (k,a)
+findMin (Bin _ kx x Tip _)  = (kx,x)
+findMin (Bin _ _  _ l _)    = findMin l
+findMin Tip                 = error "Map.findMin: empty map has no minimal element"
+
+-- | /O(log n)/. The maximal key of the map. Calls 'error' if the map is empty.
+--
+-- > findMax (fromList [(5,"a"), (3,"b")]) == (5,"a")
+-- > findMax empty                            Error: empty map has no maximal element
+
+findMax :: Map k a -> (k,a)
+findMax (Bin _ kx x _ Tip)  = (kx,x)
+findMax (Bin _ _  _ _ r)    = findMax r
+findMax Tip                 = error "Map.findMax: empty map has no maximal element"
+
+-- | /O(log n)/. Delete the minimal key. Returns an empty map if the map is empty.
+--
+-- > deleteMin (fromList [(5,"a"), (3,"b"), (7,"c")]) == fromList [(5,"a"), (7,"c")]
+-- > deleteMin empty == empty
+
+deleteMin :: Map k a -> Map k a
+deleteMin (Bin _ _  _ Tip r)  = r
+deleteMin (Bin _ kx x l r)    = balanceR kx x (deleteMin l) r
+deleteMin Tip                 = Tip
+
+-- | /O(log n)/. Delete the maximal key. Returns an empty map if the map is empty.
+--
+-- > deleteMax (fromList [(5,"a"), (3,"b"), (7,"c")]) == fromList [(3,"b"), (5,"a")]
+-- > deleteMax empty == empty
+
+deleteMax :: Map k a -> Map k a
+deleteMax (Bin _ _  _ l Tip)  = l
+deleteMax (Bin _ kx x l r)    = balanceL kx x l (deleteMax r)
+deleteMax Tip                 = Tip
+
+-- | /O(log n)/. Update the value at the minimal key.
+--
+-- > updateMin (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "Xb"), (5, "a")]
+-- > updateMin (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMin :: (a -> Maybe a) -> Map k a -> Map k a
+updateMin f m
+  = updateMinWithKey (\_ x -> f x) m
+
+-- | /O(log n)/. Update the value at the maximal key.
+--
+-- > updateMax (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "Xa")]
+-- > updateMax (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMax :: (a -> Maybe a) -> Map k a -> Map k a
+updateMax f m
+  = updateMaxWithKey (\_ x -> f x) m
+
+
+-- | /O(log n)/. Update the value at the minimal key.
+--
+-- > updateMinWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"3:b"), (5,"a")]
+-- > updateMinWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMinWithKey :: (k -> a -> Maybe a) -> Map k a -> Map k a
+updateMinWithKey _ Tip                 = Tip
+updateMinWithKey f (Bin sx kx x Tip r) = case f kx x of
+                                           Nothing -> r
+                                           Just x' -> Bin sx kx x' Tip r
+updateMinWithKey f (Bin _ kx x l r)    = balanceR kx x (updateMinWithKey f l) r
+
+-- | /O(log n)/. Update the value at the maximal key.
+--
+-- > updateMaxWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"b"), (5,"5:a")]
+-- > updateMaxWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMaxWithKey :: (k -> a -> Maybe a) -> Map k a -> Map k a
+updateMaxWithKey _ Tip                 = Tip
+updateMaxWithKey f (Bin sx kx x l Tip) = case f kx x of
+                                           Nothing -> l
+                                           Just x' -> Bin sx kx x' l Tip
+updateMaxWithKey f (Bin _ kx x l r)    = balanceL kx x l (updateMaxWithKey f r)
+
+-- | /O(log n)/. Retrieves the minimal (key,value) pair of the map, and
+-- the map stripped of that element, or 'Nothing' if passed an empty map.
+--
+-- > minViewWithKey (fromList [(5,"a"), (3,"b")]) == Just ((3,"b"), singleton 5 "a")
+-- > minViewWithKey empty == Nothing
+
+minViewWithKey :: Map k a -> Maybe ((k,a), Map k a)
+minViewWithKey Tip = Nothing
+minViewWithKey x   = Just (deleteFindMin x)
+
+-- | /O(log n)/. Retrieves the maximal (key,value) pair of the map, and
+-- the map stripped of that element, or 'Nothing' if passed an empty map.
+--
+-- > maxViewWithKey (fromList [(5,"a"), (3,"b")]) == Just ((5,"a"), singleton 3 "b")
+-- > maxViewWithKey empty == Nothing
+
+maxViewWithKey :: Map k a -> Maybe ((k,a), Map k a)
+maxViewWithKey Tip = Nothing
+maxViewWithKey x   = Just (deleteFindMax x)
+
+-- | /O(log n)/. Retrieves the value associated with minimal key of the
+-- map, and the map stripped of that element, or 'Nothing' if passed an
+-- empty map.
+--
+-- > minView (fromList [(5,"a"), (3,"b")]) == Just ("b", singleton 5 "a")
+-- > minView empty == Nothing
+
+minView :: Map k a -> Maybe (a, Map k a)
+minView Tip = Nothing
+minView x   = Just (first snd $ deleteFindMin x)
+
+-- | /O(log n)/. Retrieves the value associated with maximal key of the
+-- map, and the map stripped of that element, or 'Nothing' if passed an
+--
+-- > maxView (fromList [(5,"a"), (3,"b")]) == Just ("a", singleton 3 "b")
+-- > maxView empty == Nothing
+
+maxView :: Map k a -> Maybe (a, Map k a)
+maxView Tip = Nothing
+maxView x   = Just (first snd $ deleteFindMax x)
+
+-- Update the 1st component of a tuple (special case of Control.Arrow.first)
+first :: (a -> b) -> (a,c) -> (b,c)
+first f (x,y) = (f x, y)
+
+{--------------------------------------------------------------------
+  Union.
+--------------------------------------------------------------------}
+-- | The union of a list of maps:
+--   (@'unions' == 'Prelude.foldl' 'union' 'empty'@).
+--
+-- > unions [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+-- >     == fromList [(3, "b"), (5, "a"), (7, "C")]
+-- > unions [(fromList [(5, "A3"), (3, "B3")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "a"), (3, "b")])]
+-- >     == fromList [(3, "B3"), (5, "A3"), (7, "C")]
+
+unions :: Ord k => [Map k a] -> Map k a
+unions ts
+  = foldlStrict union empty ts
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unions #-}
+#endif
+
+-- | The union of a list of maps, with a combining operation:
+--   (@'unionsWith' f == 'Prelude.foldl' ('unionWith' f) 'empty'@).
+--
+-- > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+-- >     == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
+
+unionsWith :: Ord k => (a->a->a) -> [Map k a] -> Map k a
+unionsWith f ts
+  = foldlStrict (unionWith f) empty ts
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unionsWith #-}
+#endif
+
+-- | /O(n+m)/.
+-- The expression (@'union' t1 t2@) takes the left-biased union of @t1@ and @t2@.
+-- It prefers @t1@ when duplicate keys are encountered,
+-- i.e. (@'union' == 'unionWith' 'const'@).
+-- The implementation uses the efficient /hedge-union/ algorithm.
+--
+-- > union (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "a"), (7, "C")]
+
+union :: Ord k => Map k a -> Map k a -> Map k a
+union Tip t2  = t2
+union t1 Tip  = t1
+union t1 t2 = hedgeUnion NothingS NothingS t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE union #-}
+#endif
+
+infixl 5 `union`
+
+-- left-biased hedge union
+hedgeUnion :: Ord a => MaybeS a -> MaybeS a -> Map a b -> Map a b -> Map a b
+hedgeUnion _   _   t1  Tip = t1
+hedgeUnion blo bhi Tip (Bin _ kx x l r) = link kx x (filterGt blo l) (filterLt bhi r)
+hedgeUnion _   _   t1  (Bin _ kx x Tip Tip) = insertR kx x t1  -- According to benchmarks, this special case increases
+                                                              -- performance up to 30%. It does not help in difference or intersection.
+hedgeUnion blo bhi (Bin _ kx x l r) t2 = link kx x (hedgeUnion blo bmi l (trim blo bmi t2))
+                                                   (hedgeUnion bmi bhi r (trim bmi bhi t2))
+  where bmi = JustS kx
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE hedgeUnion #-}
+#endif
+
+{--------------------------------------------------------------------
+  Union with a combining function
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Union with a combining function. The implementation uses the efficient /hedge-union/ algorithm.
+--
+-- > unionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "aA"), (7, "C")]
+
+unionWith :: Ord k => (a -> a -> a) -> Map k a -> Map k a -> Map k a
+unionWith f m1 m2
+  = unionWithKey (\_ x y -> f x y) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unionWith #-}
+#endif
+
+-- | /O(n+m)/.
+-- Union with a combining function. The implementation uses the efficient /hedge-union/ algorithm.
+--
+-- > let f key left_value right_value = (show key) ++ ":" ++ left_value ++ "|" ++ right_value
+-- > unionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "5:a|A"), (7, "C")]
+
+unionWithKey :: Ord k => (k -> a -> a -> a) -> Map k a -> Map k a -> Map k a
+unionWithKey f t1 t2 = mergeWithKey (\k x1 x2 -> Just $ f k x1 x2) id id t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unionWithKey #-}
+#endif
+
+{--------------------------------------------------------------------
+  Difference
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Difference of two maps.
+-- Return elements of the first map not existing in the second map.
+-- The implementation uses an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > difference (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 3 "b"
+
+difference :: Ord k => Map k a -> Map k b -> Map k a
+difference Tip _   = Tip
+difference t1 Tip  = t1
+difference t1 t2   = hedgeDiff NothingS NothingS t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE difference #-}
+#endif
+
+hedgeDiff :: Ord a => MaybeS a -> MaybeS a -> Map a b -> Map a c -> Map a b
+hedgeDiff _   _   Tip              _ = Tip
+hedgeDiff blo bhi (Bin _ kx x l r) Tip = link kx x (filterGt blo l) (filterLt bhi r)
+hedgeDiff blo bhi t (Bin _ kx _ l r) = merge (hedgeDiff blo bmi (trim blo bmi t) l)
+                                             (hedgeDiff bmi bhi (trim bmi bhi t) r)
+  where bmi = JustS kx
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE hedgeDiff #-}
+#endif
+
+-- | /O(n+m)/. Difference with a combining function.
+-- When two equal keys are
+-- encountered, the combining function is applied to the values of these keys.
+-- If it returns 'Nothing', the element is discarded (proper set difference). If
+-- it returns (@'Just' y@), the element is updated with a new value @y@.
+-- The implementation uses an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > let f al ar = if al == "b" then Just (al ++ ":" ++ ar) else Nothing
+-- > differenceWith f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (7, "C")])
+-- >     == singleton 3 "b:B"
+
+differenceWith :: Ord k => (a -> b -> Maybe a) -> Map k a -> Map k b -> Map k a
+differenceWith f m1 m2
+  = differenceWithKey (\_ x y -> f x y) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE differenceWith #-}
+#endif
+
+-- | /O(n+m)/. Difference with a combining function. When two equal keys are
+-- encountered, the combining function is applied to the key and both values.
+-- If it returns 'Nothing', the element is discarded (proper set difference). If
+-- it returns (@'Just' y@), the element is updated with a new value @y@.
+-- The implementation uses an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > let f k al ar = if al == "b" then Just ((show k) ++ ":" ++ al ++ "|" ++ ar) else Nothing
+-- > differenceWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (10, "C")])
+-- >     == singleton 3 "3:b|B"
+
+differenceWithKey :: Ord k => (k -> a -> b -> Maybe a) -> Map k a -> Map k b -> Map k a
+differenceWithKey f t1 t2 = mergeWithKey f id (const Tip) t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE differenceWithKey #-}
+#endif
+
+
+{--------------------------------------------------------------------
+  Intersection
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Intersection of two maps.
+-- Return data in the first map for the keys existing in both maps.
+-- (@'intersection' m1 m2 == 'intersectionWith' 'const' m1 m2@).
+-- The implementation uses an efficient /hedge/ algorithm comparable with
+-- /hedge-union/.
+--
+-- > intersection (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "a"
+
+intersection :: Ord k => Map k a -> Map k b -> Map k a
+intersection Tip _ = Tip
+intersection _ Tip = Tip
+intersection t1 t2 = hedgeInt NothingS NothingS t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE intersection #-}
+#endif
+
+infixl 5 `intersection`
+
+hedgeInt :: Ord k => MaybeS k -> MaybeS k -> Map k a -> Map k b -> Map k a
+hedgeInt _ _ _   Tip = Tip
+hedgeInt _ _ Tip _   = Tip
+hedgeInt blo bhi (Bin _ kx x l r) t2 = let l' = hedgeInt blo bmi l (trim blo bmi t2)
+                                           r' = hedgeInt bmi bhi r (trim bmi bhi t2)
+                                       in if kx `member` t2 then link kx x l' r' else merge l' r'
+  where bmi = JustS kx
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE hedgeInt #-}
+#endif
+
+-- | /O(n+m)/. Intersection with a combining function.  The implementation uses
+-- an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > intersectionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "aA"
+
+intersectionWith :: Ord k => (a -> b -> c) -> Map k a -> Map k b -> Map k c
+intersectionWith f m1 m2
+  = intersectionWithKey (\_ x y -> f x y) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE intersectionWith #-}
+#endif
+
+-- | /O(n+m)/. Intersection with a combining function.  The implementation uses
+-- an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > let f k al ar = (show k) ++ ":" ++ al ++ "|" ++ ar
+-- > intersectionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "5:a|A"
+
+
+intersectionWithKey :: Ord k => (k -> a -> b -> c) -> Map k a -> Map k b -> Map k c
+intersectionWithKey f t1 t2 = mergeWithKey (\k x1 x2 -> Just $ f k x1 x2) (const Tip) (const Tip) t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE intersectionWithKey #-}
+#endif
+
+
+{--------------------------------------------------------------------
+  MergeWithKey
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. A high-performance universal combining function. This function
+-- is used to define 'unionWith', 'unionWithKey', 'differenceWith',
+-- 'differenceWithKey', 'intersectionWith', 'intersectionWithKey' and can be
+-- used to define other custom combine functions.
+--
+-- Please make sure you know what is going on when using 'mergeWithKey',
+-- otherwise you can be surprised by unexpected code growth or even
+-- corruption of the data structure.
+--
+-- When 'mergeWithKey' is given three arguments, it is inlined to the call
+-- site. You should therefore use 'mergeWithKey' only to define your custom
+-- combining functions. For example, you could define 'unionWithKey',
+-- 'differenceWithKey' and 'intersectionWithKey' as
+--
+-- > myUnionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) id id m1 m2
+-- > myDifferenceWithKey f m1 m2 = mergeWithKey f id (const empty) m1 m2
+-- > myIntersectionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) (const empty) (const empty) m1 m2
+--
+-- When calling @'mergeWithKey' combine only1 only2@, a function combining two
+-- 'IntMap's is created, such that
+--
+-- * if a key is present in both maps, it is passed with both corresponding
+--   values to the @combine@ function. Depending on the result, the key is either
+--   present in the result with specified value, or is left out;
+--
+-- * a nonempty subtree present only in the first map is passed to @only1@ and
+--   the output is added to the result;
+--
+-- * a nonempty subtree present only in the second map is passed to @only2@ and
+--   the output is added to the result.
+--
+-- The @only1@ and @only2@ methods /must return a map with a subset (possibly empty) of the keys of the given map/.
+-- The values can be modified arbitrarily. Most common variants of @only1@ and
+-- @only2@ are 'id' and @'const' 'empty'@, but for example @'map' f@ or
+-- @'filterWithKey' f@ could be used for any @f@.
+
+mergeWithKey :: Ord k => (k -> a -> b -> Maybe c) -> (Map k a -> Map k c) -> (Map k b -> Map k c)
+             -> Map k a -> Map k b -> Map k c
+mergeWithKey f g1 g2 = go
+  where
+    go Tip t2 = g2 t2
+    go t1 Tip = g1 t1
+    go t1 t2 = hedgeMerge NothingS NothingS t1 t2
+
+    hedgeMerge _   _   t1  Tip = g1 t1
+    hedgeMerge blo bhi Tip (Bin _ kx x l r) = g2 $ link kx x (filterGt blo l) (filterLt bhi r)
+    hedgeMerge blo bhi (Bin _ kx x l r) t2 = let l' = hedgeMerge blo bmi l (trim blo bmi t2)
+                                                 (found, trim_t2) = trimLookupLo kx bhi t2
+                                                 r' = hedgeMerge bmi bhi r trim_t2
+                                             in case found of
+                                                  Nothing -> case g1 (singleton kx x) of
+                                                               Tip -> merge l' r'
+                                                               (Bin _ _ x' Tip Tip) -> link kx x' l' r'
+                                                               _ -> error "mergeWithKey: Given function only1 does not fulfil required conditions (see documentation)"
+                                                  Just x2 -> case f kx x x2 of
+                                                               Nothing -> merge l' r'
+                                                               Just x' -> link kx x' l' r'
+      where bmi = JustS kx
+{-# INLINE mergeWithKey #-}
+
+{--------------------------------------------------------------------
+  Submap
+--------------------------------------------------------------------}
+-- | /O(n+m)/.
+-- This function is defined as (@'isSubmapOf' = 'isSubmapOfBy' (==)@).
+--
+isSubmapOf :: (Ord k,Eq a) => Map k a -> Map k a -> Bool
+isSubmapOf m1 m2 = isSubmapOfBy (==) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isSubmapOf #-}
+#endif
+
+{- | /O(n+m)/.
+ The expression (@'isSubmapOfBy' f t1 t2@) returns 'True' if
+ all keys in @t1@ are in tree @t2@, and when @f@ returns 'True' when
+ applied to their respective values. For example, the following
+ expressions are all 'True':
+
+ > isSubmapOfBy (==) (fromList [('a',1)]) (fromList [('a',1),('b',2)])
+ > isSubmapOfBy (<=) (fromList [('a',1)]) (fromList [('a',1),('b',2)])
+ > isSubmapOfBy (==) (fromList [('a',1),('b',2)]) (fromList [('a',1),('b',2)])
+
+ But the following are all 'False':
+
+ > isSubmapOfBy (==) (fromList [('a',2)]) (fromList [('a',1),('b',2)])
+ > isSubmapOfBy (<)  (fromList [('a',1)]) (fromList [('a',1),('b',2)])
+ > isSubmapOfBy (==) (fromList [('a',1),('b',2)]) (fromList [('a',1)])
+
+
+-}
+isSubmapOfBy :: Ord k => (a->b->Bool) -> Map k a -> Map k b -> Bool
+isSubmapOfBy f t1 t2
+  = (size t1 <= size t2) && (submap' f t1 t2)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isSubmapOfBy #-}
+#endif
+
+submap' :: Ord a => (b -> c -> Bool) -> Map a b -> Map a c -> Bool
+submap' _ Tip _ = True
+submap' _ _ Tip = False
+submap' f (Bin _ kx x l r) t
+  = case found of
+      Nothing -> False
+      Just y  -> f x y && submap' f l lt && submap' f r gt
+  where
+    (lt,found,gt) = splitLookup kx t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE submap' #-}
+#endif
+
+-- | /O(n+m)/. Is this a proper submap? (ie. a submap but not equal).
+-- Defined as (@'isProperSubmapOf' = 'isProperSubmapOfBy' (==)@).
+isProperSubmapOf :: (Ord k,Eq a) => Map k a -> Map k a -> Bool
+isProperSubmapOf m1 m2
+  = isProperSubmapOfBy (==) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isProperSubmapOf #-}
+#endif
+
+{- | /O(n+m)/. Is this a proper submap? (ie. a submap but not equal).
+ The expression (@'isProperSubmapOfBy' f m1 m2@) returns 'True' when
+ @m1@ and @m2@ are not equal,
+ all keys in @m1@ are in @m2@, and when @f@ returns 'True' when
+ applied to their respective values. For example, the following
+ expressions are all 'True':
+
+  > isProperSubmapOfBy (==) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+  > isProperSubmapOfBy (<=) (fromList [(1,1)]) (fromList [(1,1),(2,2)])
+
+ But the following are all 'False':
+
+  > isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)])
+  > isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1)])
+  > isProperSubmapOfBy (<)  (fromList [(1,1)])       (fromList [(1,1),(2,2)])
+
+
+-}
+isProperSubmapOfBy :: Ord k => (a -> b -> Bool) -> Map k a -> Map k b -> Bool
+isProperSubmapOfBy f t1 t2
+  = (size t1 < size t2) && (submap' f t1 t2)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isProperSubmapOfBy #-}
+#endif
+
+{--------------------------------------------------------------------
+  Filter and partition
+--------------------------------------------------------------------}
+-- | /O(n)/. Filter all values that satisfy the predicate.
+--
+-- > filter (> "a") (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > filter (> "x") (fromList [(5,"a"), (3,"b")]) == empty
+-- > filter (< "a") (fromList [(5,"a"), (3,"b")]) == empty
+
+filter :: (a -> Bool) -> Map k a -> Map k a
+filter p m
+  = filterWithKey (\_ x -> p x) m
+
+-- | /O(n)/. Filter all keys\/values that satisfy the predicate.
+--
+-- > filterWithKey (\k _ -> k > 4) (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+filterWithKey :: (k -> a -> Bool) -> Map k a -> Map k a
+filterWithKey _ Tip = Tip
+filterWithKey p (Bin _ kx x l r)
+  | p kx x    = link kx x (filterWithKey p l) (filterWithKey p r)
+  | otherwise = merge (filterWithKey p l) (filterWithKey p r)
+
+-- | /O(n)/. Partition the map according to a predicate. The first
+-- map contains all elements that satisfy the predicate, the second all
+-- elements that fail the predicate. See also 'split'.
+--
+-- > partition (> "a") (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", singleton 5 "a")
+-- > partition (< "x") (fromList [(5,"a"), (3,"b")]) == (fromList [(3, "b"), (5, "a")], empty)
+-- > partition (> "x") (fromList [(5,"a"), (3,"b")]) == (empty, fromList [(3, "b"), (5, "a")])
+
+partition :: (a -> Bool) -> Map k a -> (Map k a,Map k a)
+partition p m
+  = partitionWithKey (\_ x -> p x) m
+
+-- | /O(n)/. Partition the map according to a predicate. The first
+-- map contains all elements that satisfy the predicate, the second all
+-- elements that fail the predicate. See also 'split'.
+--
+-- > partitionWithKey (\ k _ -> k > 3) (fromList [(5,"a"), (3,"b")]) == (singleton 5 "a", singleton 3 "b")
+-- > partitionWithKey (\ k _ -> k < 7) (fromList [(5,"a"), (3,"b")]) == (fromList [(3, "b"), (5, "a")], empty)
+-- > partitionWithKey (\ k _ -> k > 7) (fromList [(5,"a"), (3,"b")]) == (empty, fromList [(3, "b"), (5, "a")])
+
+partitionWithKey :: (k -> a -> Bool) -> Map k a -> (Map k a,Map k a)
+partitionWithKey p0 t0 = toPair $ go p0 t0
+  where
+    go _ Tip = (Tip :*: Tip)
+    go p (Bin _ kx x l r)
+      | p kx x    = link kx x l1 r1 :*: merge l2 r2
+      | otherwise = merge l1 r1 :*: link kx x l2 r2
+      where
+        (l1 :*: l2) = go p l
+        (r1 :*: r2) = go p r
+
+-- | /O(n)/. Map values and collect the 'Just' results.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > mapMaybe f (fromList [(5,"a"), (3,"b")]) == singleton 5 "new a"
+
+mapMaybe :: (a -> Maybe b) -> Map k a -> Map k b
+mapMaybe f = mapMaybeWithKey (\_ x -> f x)
+
+-- | /O(n)/. Map keys\/values and collect the 'Just' results.
+--
+-- > let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
+-- > mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
+
+mapMaybeWithKey :: (k -> a -> Maybe b) -> Map k a -> Map k b
+mapMaybeWithKey _ Tip = Tip
+mapMaybeWithKey f (Bin _ kx x l r) = case f kx x of
+  Just y  -> link kx y (mapMaybeWithKey f l) (mapMaybeWithKey f r)
+  Nothing -> merge (mapMaybeWithKey f l) (mapMaybeWithKey f r)
+
+-- | /O(n)/. Map values and separate the 'Left' and 'Right' results.
+--
+-- > let f a = if a < "c" then Left a else Right a
+-- > mapEither f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(3,"b"), (5,"a")], fromList [(1,"x"), (7,"z")])
+-- >
+-- > mapEither (\ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+
+mapEither :: (a -> Either b c) -> Map k a -> (Map k b, Map k c)
+mapEither f m
+  = mapEitherWithKey (\_ x -> f x) m
+
+-- | /O(n)/. Map keys\/values and separate the 'Left' and 'Right' results.
+--
+-- > let f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
+-- > mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])
+-- >
+-- > mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])
+
+mapEitherWithKey :: (k -> a -> Either b c) -> Map k a -> (Map k b, Map k c)
+mapEitherWithKey f0 t0 = toPair $ go f0 t0
+  where
+    go _ Tip = (Tip :*: Tip)
+    go f (Bin _ kx x l r) = case f kx x of
+      Left y  -> link kx y l1 r1 :*: merge l2 r2
+      Right z -> merge l1 r1 :*: link kx z l2 r2
+     where
+        (l1 :*: l2) = go f l
+        (r1 :*: r2) = go f r
+
+{--------------------------------------------------------------------
+  Mapping
+--------------------------------------------------------------------}
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > map (++ "x") (fromList [(5,"a"), (3,"b")]) == fromList [(3, "bx"), (5, "ax")]
+
+map :: (a -> b) -> Map k a -> Map k b
+map _ Tip = Tip
+map f (Bin sx kx x l r) = Bin sx kx (f x) (map f l) (map f r)
+
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > let f key x = (show key) ++ ":" ++ x
+-- > mapWithKey f (fromList [(5,"a"), (3,"b")]) == fromList [(3, "3:b"), (5, "5:a")]
+
+mapWithKey :: (k -> a -> b) -> Map k a -> Map k b
+mapWithKey _ Tip = Tip
+mapWithKey f (Bin sx kx x l r) = Bin sx kx (f kx x) (mapWithKey f l) (mapWithKey f r)
+
+-- | /O(n)/.
+-- @'traverseWithKey' f s == 'fromList' <$> 'traverse' (\(k, v) -> (,) k <$> f k v) ('toList' m)@
+-- That is, behaves exactly like a regular 'traverse' except that the traversing
+-- function also has access to the key associated with a value.
+--
+-- > traverseWithKey (\k v -> if odd k then Just (succ v) else Nothing) (fromList [(1, 'a'), (5, 'e')]) == Just (fromList [(1, 'b'), (5, 'f')])
+-- > traverseWithKey (\k v -> if odd k then Just (succ v) else Nothing) (fromList [(2, 'c')])           == Nothing
+traverseWithKey :: Applicative t => (k -> a -> t b) -> Map k a -> t (Map k b)
+traverseWithKey f = go
+  where
+    go Tip = pure Tip
+    go (Bin 1 k v _ _) = (\v' -> Bin 1 k v' Tip Tip) <$> f k v
+    go (Bin s k v l r) = flip (Bin s k) <$> go l <*> f k v <*> go r
+{-# INLINE traverseWithKey #-}
+
+-- | /O(n)/. The function 'mapAccum' threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a b = (a ++ b, b ++ "X")
+-- > mapAccum f "Everything: " (fromList [(5,"a"), (3,"b")]) == ("Everything: ba", fromList [(3, "bX"), (5, "aX")])
+
+mapAccum :: (a -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccum f a m
+  = mapAccumWithKey (\a' _ x' -> f a' x') a m
+
+-- | /O(n)/. The function 'mapAccumWithKey' threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+-- > mapAccumWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) == ("Everything: 3-b 5-a", fromList [(3, "bX"), (5, "aX")])
+
+mapAccumWithKey :: (a -> k -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccumWithKey f a t
+  = mapAccumL f a t
+
+-- | /O(n)/. The function 'mapAccumL' threads an accumulating
+-- argument through the map in ascending order of keys.
+mapAccumL :: (a -> k -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccumL _ a Tip               = (a,Tip)
+mapAccumL f a (Bin sx kx x l r) =
+  let (a1,l') = mapAccumL f a l
+      (a2,x') = f a1 kx x
+      (a3,r') = mapAccumL f a2 r
+  in (a3,Bin sx kx x' l' r')
+
+-- | /O(n)/. The function 'mapAccumR' threads an accumulating
+-- argument through the map in descending order of keys.
+mapAccumRWithKey :: (a -> k -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccumRWithKey _ a Tip = (a,Tip)
+mapAccumRWithKey f a (Bin sx kx x l r) =
+  let (a1,r') = mapAccumRWithKey f a r
+      (a2,x') = f a1 kx x
+      (a3,l') = mapAccumRWithKey f a2 l
+  in (a3,Bin sx kx x' l' r')
+
+-- | /O(n*log n)/.
+-- @'mapKeys' f s@ is the map obtained by applying @f@ to each key of @s@.
+--
+-- The size of the result may be smaller if @f@ maps two or more distinct
+-- keys to the same new key.  In this case the value at the greatest of the
+-- original keys is retained.
+--
+-- > mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])                        == fromList [(4, "b"), (6, "a")]
+-- > mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "c"
+-- > mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "c"
+
+mapKeys :: Ord k2 => (k1->k2) -> Map k1 a -> Map k2 a
+mapKeys f = fromList . foldrWithKey (\k x xs -> (f k, x) : xs) []
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE mapKeys #-}
+#endif
+
+-- | /O(n*log n)/.
+-- @'mapKeysWith' c f s@ is the map obtained by applying @f@ to each key of @s@.
+--
+-- The size of the result may be smaller if @f@ maps two or more distinct
+-- keys to the same new key.  In this case the associated values will be
+-- combined using @c@.
+--
+-- > mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "cdab"
+-- > mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "cdab"
+
+mapKeysWith :: Ord k2 => (a -> a -> a) -> (k1->k2) -> Map k1 a -> Map k2 a
+mapKeysWith c f = fromListWith c . foldrWithKey (\k x xs -> (f k, x) : xs) []
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE mapKeysWith #-}
+#endif
+
+
+-- | /O(n)/.
+-- @'mapKeysMonotonic' f s == 'mapKeys' f s@, but works only when @f@
+-- is strictly monotonic.
+-- That is, for any values @x@ and @y@, if @x@ < @y@ then @f x@ < @f y@.
+-- /The precondition is not checked./
+-- Semi-formally, we have:
+--
+-- > and [x < y ==> f x < f y | x <- ls, y <- ls]
+-- >                     ==> mapKeysMonotonic f s == mapKeys f s
+-- >     where ls = keys s
+--
+-- This means that @f@ maps distinct original keys to distinct resulting keys.
+-- This function has better performance than 'mapKeys'.
+--
+-- > mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")]) == fromList [(6, "b"), (10, "a")]
+-- > valid (mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")])) == True
+-- > valid (mapKeysMonotonic (\ _ -> 1)     (fromList [(5,"a"), (3,"b")])) == False
+
+mapKeysMonotonic :: (k1->k2) -> Map k1 a -> Map k2 a
+mapKeysMonotonic _ Tip = Tip
+mapKeysMonotonic f (Bin sz k x l r) =
+    Bin sz (f k) x (mapKeysMonotonic f l) (mapKeysMonotonic f r)
+
+{--------------------------------------------------------------------
+  Folds
+--------------------------------------------------------------------}
+
+-- | /O(n)/. Fold the values in the map using the given right-associative
+-- binary operator, such that @'foldr' f z == 'Prelude.foldr' f z . 'elems'@.
+--
+-- For example,
+--
+-- > elems map = foldr (:) [] map
+--
+-- > let f a len = len + (length a)
+-- > foldr f 0 (fromList [(5,"a"), (3,"bbb")]) == 4
+foldr :: (a -> b -> b) -> b -> Map k a -> b
+foldr f z = go z
+  where
+    go z' Tip             = z'
+    go z' (Bin _ _ x l r) = go (f x (go z' r)) l
+{-# INLINE foldr #-}
+
+-- | /O(n)/. A strict version of 'foldr'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldr' :: (a -> b -> b) -> b -> Map k a -> b
+foldr' f z = go z
+  where
+    STRICT_1_OF_2(go)
+    go z' Tip             = z'
+    go z' (Bin _ _ x l r) = go (f x (go z' r)) l
+{-# INLINE foldr' #-}
+
+-- | /O(n)/. Fold the values in the map using the given left-associative
+-- binary operator, such that @'foldl' f z == 'Prelude.foldl' f z . 'elems'@.
+--
+-- For example,
+--
+-- > elems = reverse . foldl (flip (:)) []
+--
+-- > let f len a = len + (length a)
+-- > foldl f 0 (fromList [(5,"a"), (3,"bbb")]) == 4
+foldl :: (a -> b -> a) -> a -> Map k b -> a
+foldl f z = go z
+  where
+    go z' Tip             = z'
+    go z' (Bin _ _ x l r) = go (f (go z' l) x) r
+{-# INLINE foldl #-}
+
+-- | /O(n)/. A strict version of 'foldl'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldl' :: (a -> b -> a) -> a -> Map k b -> a
+foldl' f z = go z
+  where
+    STRICT_1_OF_2(go)
+    go z' Tip             = z'
+    go z' (Bin _ _ x l r) = go (f (go z' l) x) r
+{-# INLINE foldl' #-}
+
+-- | /O(n)/. Fold the keys and values in the map using the given right-associative
+-- binary operator, such that
+-- @'foldrWithKey' f z == 'Prelude.foldr' ('uncurry' f) z . 'toAscList'@.
+--
+-- For example,
+--
+-- > keys map = foldrWithKey (\k x ks -> k:ks) [] map
+--
+-- > let f k a result = result ++ "(" ++ (show k) ++ ":" ++ a ++ ")"
+-- > foldrWithKey f "Map: " (fromList [(5,"a"), (3,"b")]) == "Map: (5:a)(3:b)"
+foldrWithKey :: (k -> a -> b -> b) -> b -> Map k a -> b
+foldrWithKey f z = go z
+  where
+    go z' Tip             = z'
+    go z' (Bin _ kx x l r) = go (f kx x (go z' r)) l
+{-# INLINE foldrWithKey #-}
+
+-- | /O(n)/. A strict version of 'foldrWithKey'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldrWithKey' :: (k -> a -> b -> b) -> b -> Map k a -> b
+foldrWithKey' f z = go z
+  where
+    STRICT_1_OF_2(go)
+    go z' Tip              = z'
+    go z' (Bin _ kx x l r) = go (f kx x (go z' r)) l
+{-# INLINE foldrWithKey' #-}
+
+-- | /O(n)/. Fold the keys and values in the map using the given left-associative
+-- binary operator, such that
+-- @'foldlWithKey' f z == 'Prelude.foldl' (\\z' (kx, x) -> f z' kx x) z . 'toAscList'@.
+--
+-- For example,
+--
+-- > keys = reverse . foldlWithKey (\ks k x -> k:ks) []
+--
+-- > let f result k a = result ++ "(" ++ (show k) ++ ":" ++ a ++ ")"
+-- > foldlWithKey f "Map: " (fromList [(5,"a"), (3,"b")]) == "Map: (3:b)(5:a)"
+foldlWithKey :: (a -> k -> b -> a) -> a -> Map k b -> a
+foldlWithKey f z = go z
+  where
+    go z' Tip              = z'
+    go z' (Bin _ kx x l r) = go (f (go z' l) kx x) r
+{-# INLINE foldlWithKey #-}
+
+-- | /O(n)/. A strict version of 'foldlWithKey'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldlWithKey' :: (a -> k -> b -> a) -> a -> Map k b -> a
+foldlWithKey' f z = go z
+  where
+    STRICT_1_OF_2(go)
+    go z' Tip              = z'
+    go z' (Bin _ kx x l r) = go (f (go z' l) kx x) r
+{-# INLINE foldlWithKey' #-}
+
+-- | /O(n)/. Fold the keys and values in the map using the given monoid, such that
+--
+-- @'foldMapWithKey' f = 'Prelude.fold' . 'mapWithKey' f@
+--
+-- This can be an asymptotically faster than 'foldrWithKey' or 'foldlWithKey' for some monoids.
+foldMapWithKey :: Monoid m => (k -> a -> m) -> Map k a -> m
+foldMapWithKey f = go
+  where
+    go Tip             = mempty
+    go (Bin 1 k v _ _) = f k v
+    go (Bin _ k v l r) = go l `mappend` (f k v `mappend` go r)
+{-# INLINE foldMapWithKey #-}
+
+{--------------------------------------------------------------------
+  List variations
+--------------------------------------------------------------------}
+-- | /O(n)/.
+-- Return all elements of the map in the ascending order of their keys.
+-- Subject to list fusion.
+--
+-- > elems (fromList [(5,"a"), (3,"b")]) == ["b","a"]
+-- > elems empty == []
+
+elems :: Map k a -> [a]
+elems = foldr (:) []
+
+-- | /O(n)/. Return all keys of the map in ascending order. Subject to list
+-- fusion.
+--
+-- > keys (fromList [(5,"a"), (3,"b")]) == [3,5]
+-- > keys empty == []
+
+keys  :: Map k a -> [k]
+keys = foldrWithKey (\k _ ks -> k : ks) []
+
+-- | /O(n)/. An alias for 'toAscList'. Return all key\/value pairs in the map
+-- in ascending key order. Subject to list fusion.
+--
+-- > assocs (fromList [(5,"a"), (3,"b")]) == [(3,"b"), (5,"a")]
+-- > assocs empty == []
+
+assocs :: Map k a -> [(k,a)]
+assocs m
+  = toAscList m
+
+-- | /O(n)/. The set of all keys of the map.
+--
+-- > keysSet (fromList [(5,"a"), (3,"b")]) == Data.Set.fromList [3,5]
+-- > keysSet empty == Data.Set.empty
+
+keysSet :: Map k a -> Set.Set k
+keysSet Tip = Set.Tip
+keysSet (Bin sz kx _ l r) = Set.Bin sz kx (keysSet l) (keysSet r)
+
+-- | /O(n)/. Build a map from a set of keys and a function which for each key
+-- computes its value.
+--
+-- > fromSet (\k -> replicate k 'a') (Data.Set.fromList [3, 5]) == fromList [(5,"aaaaa"), (3,"aaa")]
+-- > fromSet undefined Data.Set.empty == empty
+
+fromSet :: (k -> a) -> Set.Set k -> Map k a
+fromSet _ Set.Tip = Tip
+fromSet f (Set.Bin sz x l r) = Bin sz x (f x) (fromSet f l) (fromSet f r)
+
+{--------------------------------------------------------------------
+  Lists
+  use [foldlStrict] to reduce demand on the control-stack
+--------------------------------------------------------------------}
+#if __GLASGOW_HASKELL__ >= 708
+instance (Ord k) => GHCExts.IsList (Map k v) where
+  type Item (Map k v) = (k,v)
+  fromList = fromList
+  toList   = toList
+#endif
+
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs. See also 'fromAscList'.
+-- If the list contains more than one value for the same key, the last value
+-- for the key is retained.
+--
+-- If the keys of the list are ordered, linear-time implementation is used,
+-- with the performance equal to 'fromDistinctAscList'.
+--
+-- > fromList [] == empty
+-- > fromList [(5,"a"), (3,"b"), (5, "c")] == fromList [(5,"c"), (3,"b")]
+-- > fromList [(5,"c"), (3,"b"), (5, "a")] == fromList [(5,"a"), (3,"b")]
+
+-- For some reason, when 'singleton' is used in fromList or in
+-- create, it is not inlined, so we inline it manually.
+fromList :: Ord k => [(k,a)] -> Map k a
+fromList [] = Tip
+fromList [(kx, x)] = Bin 1 kx x Tip Tip
+fromList ((kx0, x0) : xs0) | not_ordered kx0 xs0 = fromList' (Bin 1 kx0 x0 Tip Tip) xs0
+                           | otherwise = go (1::Int) (Bin 1 kx0 x0 Tip Tip) xs0
+  where
+    not_ordered _ [] = False
+    not_ordered kx ((ky,_) : _) = kx >= ky
+    {-# INLINE not_ordered #-}
+
+    fromList' t0 xs = foldlStrict ins t0 xs
+      where ins t (k,x) = insert k x t
+
+    STRICT_1_OF_3(go)
+    go _ t [] = t
+    go _ t [(kx, x)] = insertMax kx x t
+    go s l xs@((kx, x) : xss) | not_ordered kx xss = fromList' l xs
+                              | otherwise = case create s xss of
+                                  (r, ys, []) -> go (s `shiftL` 1) (link kx x l r) ys
+                                  (r, _,  ys) -> fromList' (link kx x l r) ys
+
+    -- The create is returning a triple (tree, xs, ys). Both xs and ys
+    -- represent not yet processed elements and only one of them can be nonempty.
+    -- If ys is nonempty, the keys in ys are not ordered with respect to tree
+    -- and must be inserted using fromList'. Otherwise the keys have been
+    -- ordered so far.
+    STRICT_1_OF_2(create)
+    create _ [] = (Tip, [], [])
+    create s xs@(xp : xss)
+      | s == 1 = case xp of (kx, x) | not_ordered kx xss -> (Bin 1 kx x Tip Tip, [], xss)
+                                    | otherwise -> (Bin 1 kx x Tip Tip, xss, [])
+      | otherwise = case create (s `shiftR` 1) xs of
+                      res@(_, [], _) -> res
+                      (l, [(ky, y)], zs) -> (insertMax ky y l, [], zs)
+                      (l, ys@((ky, y):yss), _) | not_ordered ky yss -> (l, [], ys)
+                                               | otherwise -> case create (s `shiftR` 1) yss of
+                                                   (r, zs, ws) -> (link ky y l r, zs, ws)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromList #-}
+#endif
+
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs with a combining function. See also 'fromAscListWith'.
+--
+-- > fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] == fromList [(3, "ab"), (5, "aba")]
+-- > fromListWith (++) [] == empty
+
+fromListWith :: Ord k => (a -> a -> a) -> [(k,a)] -> Map k a
+fromListWith f xs
+  = fromListWithKey (\_ x y -> f x y) xs
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromListWith #-}
+#endif
+
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs with a combining function. See also 'fromAscListWithKey'.
+--
+-- > let f k a1 a2 = (show k) ++ a1 ++ a2
+-- > fromListWithKey f [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] == fromList [(3, "3ab"), (5, "5a5ba")]
+-- > fromListWithKey f [] == empty
+
+fromListWithKey :: Ord k => (k -> a -> a -> a) -> [(k,a)] -> Map k a
+fromListWithKey f xs
+  = foldlStrict ins empty xs
+  where
+    ins t (k,x) = insertWithKey f k x t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromListWithKey #-}
+#endif
+
+-- | /O(n)/. Convert the map to a list of key\/value pairs. Subject to list fusion.
+--
+-- > toList (fromList [(5,"a"), (3,"b")]) == [(3,"b"), (5,"a")]
+-- > toList empty == []
+
+toList :: Map k a -> [(k,a)]
+toList = toAscList
+
+-- | /O(n)/. Convert the map to a list of key\/value pairs where the keys are
+-- in ascending order. Subject to list fusion.
+--
+-- > toAscList (fromList [(5,"a"), (3,"b")]) == [(3,"b"), (5,"a")]
+
+toAscList :: Map k a -> [(k,a)]
+toAscList = foldrWithKey (\k x xs -> (k,x):xs) []
+
+-- | /O(n)/. Convert the map to a list of key\/value pairs where the keys
+-- are in descending order. Subject to list fusion.
+--
+-- > toDescList (fromList [(5,"a"), (3,"b")]) == [(5,"a"), (3,"b")]
+
+toDescList :: Map k a -> [(k,a)]
+toDescList = foldlWithKey (\xs k x -> (k,x):xs) []
+
+-- List fusion for the list generating functions.
+#if __GLASGOW_HASKELL__
+-- The foldrFB and foldlFB are fold{r,l}WithKey equivalents, used for list fusion.
+-- They are important to convert unfused methods back, see mapFB in prelude.
+foldrFB :: (k -> a -> b -> b) -> b -> Map k a -> b
+foldrFB = foldrWithKey
+{-# INLINE[0] foldrFB #-}
+foldlFB :: (a -> k -> b -> a) -> a -> Map k b -> a
+foldlFB = foldlWithKey
+{-# INLINE[0] foldlFB #-}
+
+-- Inline assocs and toList, so that we need to fuse only toAscList.
+{-# INLINE assocs #-}
+{-# INLINE toList #-}
+
+-- The fusion is enabled up to phase 2 included. If it does not succeed,
+-- convert in phase 1 the expanded elems,keys,to{Asc,Desc}List calls back to
+-- elems,keys,to{Asc,Desc}List.  In phase 0, we inline fold{lr}FB (which were
+-- used in a list fusion, otherwise it would go away in phase 1), and let compiler
+-- do whatever it wants with elems,keys,to{Asc,Desc}List -- it was forbidden to
+-- inline it before phase 0, otherwise the fusion rules would not fire at all.
+{-# NOINLINE[0] elems #-}
+{-# NOINLINE[0] keys #-}
+{-# NOINLINE[0] toAscList #-}
+{-# NOINLINE[0] toDescList #-}
+{-# RULES "Map.elems" [~1] forall m . elems m = build (\c n -> foldrFB (\_ x xs -> c x xs) n m) #-}
+{-# RULES "Map.elemsBack" [1] foldrFB (\_ x xs -> x : xs) [] = elems #-}
+{-# RULES "Map.keys" [~1] forall m . keys m = build (\c n -> foldrFB (\k _ xs -> c k xs) n m) #-}
+{-# RULES "Map.keysBack" [1] foldrFB (\k _ xs -> k : xs) [] = keys #-}
+{-# RULES "Map.toAscList" [~1] forall m . toAscList m = build (\c n -> foldrFB (\k x xs -> c (k,x) xs) n m) #-}
+{-# RULES "Map.toAscListBack" [1] foldrFB (\k x xs -> (k, x) : xs) [] = toAscList #-}
+{-# RULES "Map.toDescList" [~1] forall m . toDescList m = build (\c n -> foldlFB (\xs k x -> c (k,x) xs) n m) #-}
+{-# RULES "Map.toDescListBack" [1] foldlFB (\xs k x -> (k, x) : xs) [] = toDescList #-}
+#endif
+
+{--------------------------------------------------------------------
+  Building trees from ascending/descending lists can be done in linear time.
+
+  Note that if [xs] is ascending that:
+    fromAscList xs       == fromList xs
+    fromAscListWith f xs == fromListWith f xs
+--------------------------------------------------------------------}
+-- | /O(n)/. Build a map from an ascending list in linear time.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscList [(3,"b"), (5,"a")]          == fromList [(3, "b"), (5, "a")]
+-- > fromAscList [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "b")]
+-- > valid (fromAscList [(3,"b"), (5,"a"), (5,"b")]) == True
+-- > valid (fromAscList [(5,"a"), (3,"b"), (5,"b")]) == False
+
+fromAscList :: Eq k => [(k,a)] -> Map k a
+fromAscList xs
+  = fromAscListWithKey (\_ x _ -> x) xs
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscList #-}
+#endif
+
+-- | /O(n)/. Build a map from an ascending list in linear time with a combining function for equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "ba")]
+-- > valid (fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")]) == True
+-- > valid (fromAscListWith (++) [(5,"a"), (3,"b"), (5,"b")]) == False
+
+fromAscListWith :: Eq k => (a -> a -> a) -> [(k,a)] -> Map k a
+fromAscListWith f xs
+  = fromAscListWithKey (\_ x y -> f x y) xs
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscListWith #-}
+#endif
+
+-- | /O(n)/. Build a map from an ascending list in linear time with a
+-- combining function for equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > let f k a1 a2 = (show k) ++ ":" ++ a1 ++ a2
+-- > fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")] == fromList [(3, "b"), (5, "5:b5:ba")]
+-- > valid (fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")]) == True
+-- > valid (fromAscListWithKey f [(5,"a"), (3,"b"), (5,"b"), (5,"b")]) == False
+
+fromAscListWithKey :: Eq k => (k -> a -> a -> a) -> [(k,a)] -> Map k a
+fromAscListWithKey f xs
+  = fromDistinctAscList (combineEq f xs)
+  where
+  -- [combineEq f xs] combines equal elements with function [f] in an ordered list [xs]
+  combineEq _ xs'
+    = case xs' of
+        []     -> []
+        [x]    -> [x]
+        (x:xx) -> combineEq' x xx
+
+  combineEq' z [] = [z]
+  combineEq' z@(kz,zz) (x@(kx,xx):xs')
+    | kx==kz    = let yy = f kx xx zz in combineEq' (kx,yy) xs'
+    | otherwise = z:combineEq' x xs'
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscListWithKey #-}
+#endif
+
+
+-- | /O(n)/. Build a map from an ascending list of distinct elements in linear time.
+-- /The precondition is not checked./
+--
+-- > fromDistinctAscList [(3,"b"), (5,"a")] == fromList [(3, "b"), (5, "a")]
+-- > valid (fromDistinctAscList [(3,"b"), (5,"a")])          == True
+-- > valid (fromDistinctAscList [(3,"b"), (5,"a"), (5,"b")]) == False
+
+-- For some reason, when 'singleton' is used in fromDistinctAscList or in
+-- create, it is not inlined, so we inline it manually.
+fromDistinctAscList :: [(k,a)] -> Map k a
+fromDistinctAscList [] = Tip
+fromDistinctAscList ((kx0, x0) : xs0) = go (1::Int) (Bin 1 kx0 x0 Tip Tip) xs0
+  where
+    STRICT_1_OF_3(go)
+    go _ t [] = t
+    go s l ((kx, x) : xs) = case create s xs of
+                              (r, ys) -> go (s `shiftL` 1) (link kx x l r) ys
+
+    STRICT_1_OF_2(create)
+    create _ [] = (Tip, [])
+    create s xs@(x' : xs')
+      | s == 1 = case x' of (kx, x) -> (Bin 1 kx x Tip Tip, xs')
+      | otherwise = case create (s `shiftR` 1) xs of
+                      res@(_, []) -> res
+                      (l, (ky, y):ys) -> case create (s `shiftR` 1) ys of
+                        (r, zs) -> (link ky y l r, zs)
+
+
+{--------------------------------------------------------------------
+  Utility functions that return sub-ranges of the original
+  tree. Some functions take a `Maybe value` as an argument to
+  allow comparisons against infinite values. These are called `blow`
+  (Nothing is -\infty) and `bhigh` (here Nothing is +\infty).
+  We use MaybeS value, which is a Maybe strict in the Just case.
+
+  [trim blow bhigh t]   A tree that is either empty or where [x > blow]
+                        and [x < bhigh] for the value [x] of the root.
+  [filterGt blow t]     A tree where for all values [k]. [k > blow]
+  [filterLt bhigh t]    A tree where for all values [k]. [k < bhigh]
+
+  [split k t]           Returns two trees [l] and [r] where all keys
+                        in [l] are <[k] and all keys in [r] are >[k].
+  [splitLookup k t]     Just like [split] but also returns whether [k]
+                        was found in the tree.
+--------------------------------------------------------------------}
+
+data MaybeS a = NothingS | JustS !a
+
+{--------------------------------------------------------------------
+  [trim blo bhi t] trims away all subtrees that surely contain no
+  values between the range [blo] to [bhi]. The returned tree is either
+  empty or the key of the root is between @blo@ and @bhi@.
+--------------------------------------------------------------------}
+trim :: Ord k => MaybeS k -> MaybeS k -> Map k a -> Map k a
+trim NothingS   NothingS   t = t
+trim (JustS lk) NothingS   t = greater lk t where greater lo (Bin _ k _ _ r) | k <= lo = greater lo r
+                                                  greater _  t' = t'
+trim NothingS   (JustS hk) t = lesser hk t  where lesser  hi (Bin _ k _ l _) | k >= hi = lesser  hi l
+                                                  lesser  _  t' = t'
+trim (JustS lk) (JustS hk) t = middle lk hk t  where middle lo hi (Bin _ k _ _ r) | k <= lo = middle lo hi r
+                                                     middle lo hi (Bin _ k _ l _) | k >= hi = middle lo hi l
+                                                     middle _  _  t' = t'
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE trim #-}
+#endif
+
+-- Helper function for 'mergeWithKey'. The @'trimLookupLo' lk hk t@ performs both
+-- @'trim' (JustS lk) hk t@ and @'lookup' lk t@.
+
+-- See Note: Type of local 'go' function
+trimLookupLo :: Ord k => k -> MaybeS k -> Map k a -> (Maybe a, Map k a)
+trimLookupLo lk0 mhk0 t0 = toPair $ go lk0 mhk0 t0
+  where
+    go lk NothingS t = greater lk t
+      where greater :: Ord k => k -> Map k a -> StrictPair (Maybe a) (Map k a)
+            greater lo t'@(Bin _ kx x l r) = case compare lo kx of
+                LT -> lookup lo l :*: t'
+                EQ -> (Just x :*: r)
+                GT -> greater lo r
+            greater _ Tip = (Nothing :*: Tip)
+    go lk (JustS hk) t = middle lk hk t
+      where middle :: Ord k => k -> k -> Map k a -> StrictPair (Maybe a) (Map k a)
+            middle lo hi t'@(Bin _ kx x l r) = case compare lo kx of
+                LT | kx < hi -> lookup lo l :*: t'
+                   | otherwise -> middle lo hi l
+                EQ -> Just x :*: lesser hi r
+                GT -> middle lo hi r
+            middle _ _ Tip = (Nothing :*: Tip)
+
+            lesser :: Ord k => k -> Map k a -> Map k a
+            lesser hi (Bin _ k _ l _) | k >= hi = lesser hi l
+            lesser _ t' = t'
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE trimLookupLo #-}
+#endif
+
+
+{--------------------------------------------------------------------
+  [filterGt b t] filter all keys >[b] from tree [t]
+  [filterLt b t] filter all keys <[b] from tree [t]
+--------------------------------------------------------------------}
+filterGt :: Ord k => MaybeS k -> Map k v -> Map k v
+filterGt NothingS t = t
+filterGt (JustS b) t = filter' b t
+  where filter' _   Tip = Tip
+        filter' b' (Bin _ kx x l r) =
+          case compare b' kx of LT -> link kx x (filter' b' l) r
+                                EQ -> r
+                                GT -> filter' b' r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE filterGt #-}
+#endif
+
+filterLt :: Ord k => MaybeS k -> Map k v -> Map k v
+filterLt NothingS t = t
+filterLt (JustS b) t = filter' b t
+  where filter' _   Tip = Tip
+        filter' b' (Bin _ kx x l r) =
+          case compare kx b' of LT -> link kx x l (filter' b' r)
+                                EQ -> l
+                                GT -> filter' b' l
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE filterLt #-}
+#endif
+
+{--------------------------------------------------------------------
+  Split
+--------------------------------------------------------------------}
+-- | /O(log n)/. The expression (@'split' k map@) is a pair @(map1,map2)@ where
+-- the keys in @map1@ are smaller than @k@ and the keys in @map2@ larger than @k@.
+-- Any key equal to @k@ is found in neither @map1@ nor @map2@.
+--
+-- > split 2 (fromList [(5,"a"), (3,"b")]) == (empty, fromList [(3,"b"), (5,"a")])
+-- > split 3 (fromList [(5,"a"), (3,"b")]) == (empty, singleton 5 "a")
+-- > split 4 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", singleton 5 "a")
+-- > split 5 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", empty)
+-- > split 6 (fromList [(5,"a"), (3,"b")]) == (fromList [(3,"b"), (5,"a")], empty)
+
+split :: Ord k => k -> Map k a -> (Map k a,Map k a)
+split k0 t0 = k0 `seq` toPair $ go k0 t0
+  where
+    go k t =
+      case t of
+        Tip            -> (Tip :*: Tip)
+        Bin _ kx x l r -> case compare k kx of
+          LT -> let (lt :*: gt) = go k l in lt :*: link kx x gt r
+          GT -> let (lt :*: gt) = go k r in link kx x l lt :*: gt
+          EQ -> (l :*: r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE split #-}
+#endif
+
+-- | /O(log n)/. The expression (@'splitLookup' k map@) splits a map just
+-- like 'split' but also returns @'lookup' k map@.
+--
+-- > splitLookup 2 (fromList [(5,"a"), (3,"b")]) == (empty, Nothing, fromList [(3,"b"), (5,"a")])
+-- > splitLookup 3 (fromList [(5,"a"), (3,"b")]) == (empty, Just "b", singleton 5 "a")
+-- > splitLookup 4 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", Nothing, singleton 5 "a")
+-- > splitLookup 5 (fromList [(5,"a"), (3,"b")]) == (singleton 3 "b", Just "a", empty)
+-- > splitLookup 6 (fromList [(5,"a"), (3,"b")]) == (fromList [(3,"b"), (5,"a")], Nothing, empty)
+
+splitLookup :: Ord k => k -> Map k a -> (Map k a,Maybe a,Map k a)
+splitLookup k t = k `seq`
+  case t of
+    Tip            -> (Tip,Nothing,Tip)
+    Bin _ kx x l r -> case compare k kx of
+      LT -> let (lt,z,gt) = splitLookup k l
+                gt' = link kx x gt r
+            in gt' `seq` (lt,z,gt')
+      GT -> let (lt,z,gt) = splitLookup k r
+                lt' = link kx x l lt
+            in lt' `seq` (lt',z,gt)
+      EQ -> (l,Just x,r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE splitLookup #-}
+#endif
+
+{--------------------------------------------------------------------
+  Utility functions that maintain the balance properties of the tree.
+  All constructors assume that all values in [l] < [k] and all values
+  in [r] > [k], and that [l] and [r] are valid trees.
+
+  In order of sophistication:
+    [Bin sz k x l r]  The type constructor.
+    [bin k x l r]     Maintains the correct size, assumes that both [l]
+                      and [r] are balanced with respect to each other.
+    [balance k x l r] Restores the balance and size.
+                      Assumes that the original tree was balanced and
+                      that [l] or [r] has changed by at most one element.
+    [link k x l r]    Restores balance and size.
+
+  Furthermore, we can construct a new tree from two trees. Both operations
+  assume that all values in [l] < all values in [r] and that [l] and [r]
+  are valid:
+    [glue l r]        Glues [l] and [r] together. Assumes that [l] and
+                      [r] are already balanced with respect to each other.
+    [merge l r]       Merges two trees and restores balance.
+
+  Note: in contrast to Adam's paper, we use (<=) comparisons instead
+  of (<) comparisons in [link], [merge] and [balance].
+  Quickcheck (on [difference]) showed that this was necessary in order
+  to maintain the invariants. It is quite unsatisfactory that I haven't
+  been able to find out why this is actually the case! Fortunately, it
+  doesn't hurt to be a bit more conservative.
+--------------------------------------------------------------------}
+
+{--------------------------------------------------------------------
+  Link
+--------------------------------------------------------------------}
+link :: k -> a -> Map k a -> Map k a -> Map k a
+link kx x Tip r  = insertMin kx x r
+link kx x l Tip  = insertMax kx x l
+link kx x l@(Bin sizeL ky y ly ry) r@(Bin sizeR kz z lz rz)
+  | delta*sizeL < sizeR  = balanceL kz z (link kx x l lz) rz
+  | delta*sizeR < sizeL  = balanceR ky y ly (link kx x ry r)
+  | otherwise            = bin kx x l r
+
+
+-- insertMin and insertMax don't perform potentially expensive comparisons.
+insertMax,insertMin :: k -> a -> Map k a -> Map k a
+insertMax kx x t
+  = case t of
+      Tip -> singleton kx x
+      Bin _ ky y l r
+          -> balanceR ky y l (insertMax kx x r)
+
+insertMin kx x t
+  = case t of
+      Tip -> singleton kx x
+      Bin _ ky y l r
+          -> balanceL ky y (insertMin kx x l) r
+
+{--------------------------------------------------------------------
+  [merge l r]: merges two trees.
+--------------------------------------------------------------------}
+merge :: Map k a -> Map k a -> Map k a
+merge Tip r   = r
+merge l Tip   = l
+merge l@(Bin sizeL kx x lx rx) r@(Bin sizeR ky y ly ry)
+  | delta*sizeL < sizeR = balanceL ky y (merge l ly) ry
+  | delta*sizeR < sizeL = balanceR kx x lx (merge rx r)
+  | otherwise           = glue l r
+
+{--------------------------------------------------------------------
+  [glue l r]: glues two trees together.
+  Assumes that [l] and [r] are already balanced with respect to each other.
+--------------------------------------------------------------------}
+glue :: Map k a -> Map k a -> Map k a
+glue Tip r = r
+glue l Tip = l
+glue l r
+  | size l > size r = let ((km,m),l') = deleteFindMax l in balanceR km m l' r
+  | otherwise       = let ((km,m),r') = deleteFindMin r in balanceL km m l r'
+
+
+-- | /O(log n)/. Delete and find the minimal element.
+--
+-- > deleteFindMin (fromList [(5,"a"), (3,"b"), (10,"c")]) == ((3,"b"), fromList[(5,"a"), (10,"c")])
+-- > deleteFindMin                                            Error: can not return the minimal element of an empty map
+
+deleteFindMin :: Map k a -> ((k,a),Map k a)
+deleteFindMin t
+  = case t of
+      Bin _ k x Tip r -> ((k,x),r)
+      Bin _ k x l r   -> let (km,l') = deleteFindMin l in (km,balanceR k x l' r)
+      Tip             -> (error "Map.deleteFindMin: can not return the minimal element of an empty map", Tip)
+
+-- | /O(log n)/. Delete and find the maximal element.
+--
+-- > deleteFindMax (fromList [(5,"a"), (3,"b"), (10,"c")]) == ((10,"c"), fromList [(3,"b"), (5,"a")])
+-- > deleteFindMax empty                                      Error: can not return the maximal element of an empty map
+
+deleteFindMax :: Map k a -> ((k,a),Map k a)
+deleteFindMax t
+  = case t of
+      Bin _ k x l Tip -> ((k,x),l)
+      Bin _ k x l r   -> let (km,r') = deleteFindMax r in (km,balanceL k x l r')
+      Tip             -> (error "Map.deleteFindMax: can not return the maximal element of an empty map", Tip)
+
+
+{--------------------------------------------------------------------
+  [balance l x r] balances two trees with value x.
+  The sizes of the trees should balance after decreasing the
+  size of one of them. (a rotation).
+
+  [delta] is the maximal relative difference between the sizes of
+          two trees, it corresponds with the [w] in Adams' paper.
+  [ratio] is the ratio between an outer and inner sibling of the
+          heavier subtree in an unbalanced setting. It determines
+          whether a double or single rotation should be performed
+          to restore balance. It is corresponds with the inverse
+          of $\alpha$ in Adam's article.
+
+  Note that according to the Adam's paper:
+  - [delta] should be larger than 4.646 with a [ratio] of 2.
+  - [delta] should be larger than 3.745 with a [ratio] of 1.534.
+
+  But the Adam's paper is erroneous:
+  - It can be proved that for delta=2 and delta>=5 there does
+    not exist any ratio that would work.
+  - Delta=4.5 and ratio=2 does not work.
+
+  That leaves two reasonable variants, delta=3 and delta=4,
+  both with ratio=2.
+
+  - A lower [delta] leads to a more 'perfectly' balanced tree.
+  - A higher [delta] performs less rebalancing.
+
+  In the benchmarks, delta=3 is faster on insert operations,
+  and delta=4 has slightly better deletes. As the insert speedup
+  is larger, we currently use delta=3.
+
+--------------------------------------------------------------------}
+delta,ratio :: Int
+delta = 3
+ratio = 2
+
+-- The balance function is equivalent to the following:
+--
+--   balance :: k -> a -> Map k a -> Map k a -> Map k a
+--   balance k x l r
+--     | sizeL + sizeR <= 1    = Bin sizeX k x l r
+--     | sizeR > delta*sizeL   = rotateL k x l r
+--     | sizeL > delta*sizeR   = rotateR k x l r
+--     | otherwise             = Bin sizeX k x l r
+--     where
+--       sizeL = size l
+--       sizeR = size r
+--       sizeX = sizeL + sizeR + 1
+--
+--   rotateL :: a -> b -> Map a b -> Map a b -> Map a b
+--   rotateL k x l r@(Bin _ _ _ ly ry) | size ly < ratio*size ry = singleL k x l r
+--                                     | otherwise               = doubleL k x l r
+--
+--   rotateR :: a -> b -> Map a b -> Map a b -> Map a b
+--   rotateR k x l@(Bin _ _ _ ly ry) r | size ry < ratio*size ly = singleR k x l r
+--                                     | otherwise               = doubleR k x l r
+--
+--   singleL, singleR :: a -> b -> Map a b -> Map a b -> Map a b
+--   singleL k1 x1 t1 (Bin _ k2 x2 t2 t3)  = bin k2 x2 (bin k1 x1 t1 t2) t3
+--   singleR k1 x1 (Bin _ k2 x2 t1 t2) t3  = bin k2 x2 t1 (bin k1 x1 t2 t3)
+--
+--   doubleL, doubleR :: a -> b -> Map a b -> Map a b -> Map a b
+--   doubleL k1 x1 t1 (Bin _ k2 x2 (Bin _ k3 x3 t2 t3) t4) = bin k3 x3 (bin k1 x1 t1 t2) (bin k2 x2 t3 t4)
+--   doubleR k1 x1 (Bin _ k2 x2 t1 (Bin _ k3 x3 t2 t3)) t4 = bin k3 x3 (bin k2 x2 t1 t2) (bin k1 x1 t3 t4)
+--
+-- It is only written in such a way that every node is pattern-matched only once.
+
+balance :: k -> a -> Map k a -> Map k a -> Map k a
+balance k x l r = case l of
+  Tip -> case r of
+           Tip -> Bin 1 k x Tip Tip
+           (Bin _ _ _ Tip Tip) -> Bin 2 k x Tip r
+           (Bin _ rk rx Tip rr@(Bin _ _ _ _ _)) -> Bin 3 rk rx (Bin 1 k x Tip Tip) rr
+           (Bin _ rk rx (Bin _ rlk rlx _ _) Tip) -> Bin 3 rlk rlx (Bin 1 k x Tip Tip) (Bin 1 rk rx Tip Tip)
+           (Bin rs rk rx rl@(Bin rls rlk rlx rll rlr) rr@(Bin rrs _ _ _ _))
+             | rls < ratio*rrs -> Bin (1+rs) rk rx (Bin (1+rls) k x Tip rl) rr
+             | otherwise -> Bin (1+rs) rlk rlx (Bin (1+size rll) k x Tip rll) (Bin (1+rrs+size rlr) rk rx rlr rr)
+
+  (Bin ls lk lx ll lr) -> case r of
+           Tip -> case (ll, lr) of
+                    (Tip, Tip) -> Bin 2 k x l Tip
+                    (Tip, (Bin _ lrk lrx _ _)) -> Bin 3 lrk lrx (Bin 1 lk lx Tip Tip) (Bin 1 k x Tip Tip)
+                    ((Bin _ _ _ _ _), Tip) -> Bin 3 lk lx ll (Bin 1 k x Tip Tip)
+                    ((Bin lls _ _ _ _), (Bin lrs lrk lrx lrl lrr))
+                      | lrs < ratio*lls -> Bin (1+ls) lk lx ll (Bin (1+lrs) k x lr Tip)
+                      | otherwise -> Bin (1+ls) lrk lrx (Bin (1+lls+size lrl) lk lx ll lrl) (Bin (1+size lrr) k x lrr Tip)
+           (Bin rs rk rx rl rr)
+              | rs > delta*ls  -> case (rl, rr) of
+                   (Bin rls rlk rlx rll rlr, Bin rrs _ _ _ _)
+                     | rls < ratio*rrs -> Bin (1+ls+rs) rk rx (Bin (1+ls+rls) k x l rl) rr
+                     | otherwise -> Bin (1+ls+rs) rlk rlx (Bin (1+ls+size rll) k x l rll) (Bin (1+rrs+size rlr) rk rx rlr rr)
+                   (_, _) -> error "Failure in Data.Map.balance"
+              | ls > delta*rs  -> case (ll, lr) of
+                   (Bin lls _ _ _ _, Bin lrs lrk lrx lrl lrr)
+                     | lrs < ratio*lls -> Bin (1+ls+rs) lk lx ll (Bin (1+rs+lrs) k x lr r)
+                     | otherwise -> Bin (1+ls+rs) lrk lrx (Bin (1+lls+size lrl) lk lx ll lrl) (Bin (1+rs+size lrr) k x lrr r)
+                   (_, _) -> error "Failure in Data.Map.balance"
+              | otherwise -> Bin (1+ls+rs) k x l r
+{-# NOINLINE balance #-}
+
+-- Functions balanceL and balanceR are specialised versions of balance.
+-- balanceL only checks whether the left subtree is too big,
+-- balanceR only checks whether the right subtree is too big.
+
+-- balanceL is called when left subtree might have been inserted to or when
+-- right subtree might have been deleted from.
+balanceL :: k -> a -> Map k a -> Map k a -> Map k a
+balanceL k x l r = case r of
+  Tip -> case l of
+           Tip -> Bin 1 k x Tip Tip
+           (Bin _ _ _ Tip Tip) -> Bin 2 k x l Tip
+           (Bin _ lk lx Tip (Bin _ lrk lrx _ _)) -> Bin 3 lrk lrx (Bin 1 lk lx Tip Tip) (Bin 1 k x Tip Tip)
+           (Bin _ lk lx ll@(Bin _ _ _ _ _) Tip) -> Bin 3 lk lx ll (Bin 1 k x Tip Tip)
+           (Bin ls lk lx ll@(Bin lls _ _ _ _) lr@(Bin lrs lrk lrx lrl lrr))
+             | lrs < ratio*lls -> Bin (1+ls) lk lx ll (Bin (1+lrs) k x lr Tip)
+             | otherwise -> Bin (1+ls) lrk lrx (Bin (1+lls+size lrl) lk lx ll lrl) (Bin (1+size lrr) k x lrr Tip)
+
+  (Bin rs _ _ _ _) -> case l of
+           Tip -> Bin (1+rs) k x Tip r
+
+           (Bin ls lk lx ll lr)
+              | ls > delta*rs  -> case (ll, lr) of
+                   (Bin lls _ _ _ _, Bin lrs lrk lrx lrl lrr)
+                     | lrs < ratio*lls -> Bin (1+ls+rs) lk lx ll (Bin (1+rs+lrs) k x lr r)
+                     | otherwise -> Bin (1+ls+rs) lrk lrx (Bin (1+lls+size lrl) lk lx ll lrl) (Bin (1+rs+size lrr) k x lrr r)
+                   (_, _) -> error "Failure in Data.Map.balanceL"
+              | otherwise -> Bin (1+ls+rs) k x l r
+{-# NOINLINE balanceL #-}
+
+-- balanceR is called when right subtree might have been inserted to or when
+-- left subtree might have been deleted from.
+balanceR :: k -> a -> Map k a -> Map k a -> Map k a
+balanceR k x l r = case l of
+  Tip -> case r of
+           Tip -> Bin 1 k x Tip Tip
+           (Bin _ _ _ Tip Tip) -> Bin 2 k x Tip r
+           (Bin _ rk rx Tip rr@(Bin _ _ _ _ _)) -> Bin 3 rk rx (Bin 1 k x Tip Tip) rr
+           (Bin _ rk rx (Bin _ rlk rlx _ _) Tip) -> Bin 3 rlk rlx (Bin 1 k x Tip Tip) (Bin 1 rk rx Tip Tip)
+           (Bin rs rk rx rl@(Bin rls rlk rlx rll rlr) rr@(Bin rrs _ _ _ _))
+             | rls < ratio*rrs -> Bin (1+rs) rk rx (Bin (1+rls) k x Tip rl) rr
+             | otherwise -> Bin (1+rs) rlk rlx (Bin (1+size rll) k x Tip rll) (Bin (1+rrs+size rlr) rk rx rlr rr)
+
+  (Bin ls _ _ _ _) -> case r of
+           Tip -> Bin (1+ls) k x l Tip
+
+           (Bin rs rk rx rl rr)
+              | rs > delta*ls  -> case (rl, rr) of
+                   (Bin rls rlk rlx rll rlr, Bin rrs _ _ _ _)
+                     | rls < ratio*rrs -> Bin (1+ls+rs) rk rx (Bin (1+ls+rls) k x l rl) rr
+                     | otherwise -> Bin (1+ls+rs) rlk rlx (Bin (1+ls+size rll) k x l rll) (Bin (1+rrs+size rlr) rk rx rlr rr)
+                   (_, _) -> error "Failure in Data.Map.balanceR"
+              | otherwise -> Bin (1+ls+rs) k x l r
+{-# NOINLINE balanceR #-}
+
+
+{--------------------------------------------------------------------
+  The bin constructor maintains the size of the tree
+--------------------------------------------------------------------}
+bin :: k -> a -> Map k a -> Map k a -> Map k a
+bin k x l r
+  = Bin (size l + size r + 1) k x l r
+{-# INLINE bin #-}
+
+
+{--------------------------------------------------------------------
+  Eq converts the tree to a list. In a lazy setting, this
+  actually seems one of the faster methods to compare two trees
+  and it is certainly the simplest :-)
+--------------------------------------------------------------------}
+instance (Eq k,Eq a) => Eq (Map k a) where
+  t1 == t2  = (size t1 == size t2) && (toAscList t1 == toAscList t2)
+
+{--------------------------------------------------------------------
+  Ord
+--------------------------------------------------------------------}
+
+instance (Ord k, Ord v) => Ord (Map k v) where
+    compare m1 m2 = compare (toAscList m1) (toAscList m2)
+
+{--------------------------------------------------------------------
+  Functor
+--------------------------------------------------------------------}
+instance Functor (Map k) where
+  fmap f m  = map f m
+
+instance Traversable (Map k) where
+  traverse f = traverseWithKey (\_ -> f)
+  {-# INLINE traverse #-}
+
+instance Foldable.Foldable (Map k) where
+  fold t = go t
+    where go Tip = mempty
+          go (Bin 1 _ v _ _) = v
+          go (Bin _ _ v l r) = go l `mappend` (v `mappend` go r)
+  {-# INLINABLE fold #-}
+  foldr = foldr
+  {-# INLINE foldr #-}
+  foldl = foldl
+  {-# INLINE foldl #-}
+  foldMap f t = go t
+    where go Tip = mempty
+          go (Bin 1 _ v _ _) = f v
+          go (Bin _ _ v l r) = go l `mappend` (f v `mappend` go r)
+  {-# INLINE foldMap #-}
+
+instance (NFData k, NFData a) => NFData (Map k a) where
+    rnf Tip = ()
+    rnf (Bin _ kx x l r) = rnf kx `seq` rnf x `seq` rnf l `seq` rnf r
+
+{--------------------------------------------------------------------
+  Read
+--------------------------------------------------------------------}
+instance (Ord k, Read k, Read e) => Read (Map k e) where
+#ifdef __GLASGOW_HASKELL__
+  readPrec = parens $ prec 10 $ do
+    Ident "fromList" <- lexP
+    xs <- readPrec
+    return (fromList xs)
+
+  readListPrec = readListPrecDefault
+#else
+  readsPrec p = readParen (p > 10) $ \ r -> do
+    ("fromList",s) <- lex r
+    (xs,t) <- reads s
+    return (fromList xs,t)
+#endif
+
+{--------------------------------------------------------------------
+  Show
+--------------------------------------------------------------------}
+instance (Show k, Show a) => Show (Map k a) where
+  showsPrec d m  = showParen (d > 10) $
+    showString "fromList " . shows (toList m)
+
+-- | /O(n)/. Show the tree that implements the map. The tree is shown
+-- in a compressed, hanging format. See 'showTreeWith'.
+showTree :: (Show k,Show a) => Map k a -> String
+showTree m
+  = showTreeWith showElem True False m
+  where
+    showElem k x  = show k ++ ":=" ++ show x
+
+
+{- | /O(n)/. The expression (@'showTreeWith' showelem hang wide map@) shows
+ the tree that implements the map. Elements are shown using the @showElem@ function. If @hang@ is
+ 'True', a /hanging/ tree is shown otherwise a rotated tree is shown. If
+ @wide@ is 'True', an extra wide version is shown.
+
+>  Map> let t = fromDistinctAscList [(x,()) | x <- [1..5]]
+>  Map> putStrLn $ showTreeWith (\k x -> show (k,x)) True False t
+>  (4,())
+>  +--(2,())
+>  |  +--(1,())
+>  |  +--(3,())
+>  +--(5,())
+>
+>  Map> putStrLn $ showTreeWith (\k x -> show (k,x)) True True t
+>  (4,())
+>  |
+>  +--(2,())
+>  |  |
+>  |  +--(1,())
+>  |  |
+>  |  +--(3,())
+>  |
+>  +--(5,())
+>
+>  Map> putStrLn $ showTreeWith (\k x -> show (k,x)) False True t
+>  +--(5,())
+>  |
+>  (4,())
+>  |
+>  |  +--(3,())
+>  |  |
+>  +--(2,())
+>     |
+>     +--(1,())
+
+-}
+showTreeWith :: (k -> a -> String) -> Bool -> Bool -> Map k a -> String
+showTreeWith showelem hang wide t
+  | hang      = (showsTreeHang showelem wide [] t) ""
+  | otherwise = (showsTree showelem wide [] [] t) ""
+
+showsTree :: (k -> a -> String) -> Bool -> [String] -> [String] -> Map k a -> ShowS
+showsTree showelem wide lbars rbars t
+  = case t of
+      Tip -> showsBars lbars . showString "|\n"
+      Bin _ kx x Tip Tip
+          -> showsBars lbars . showString (showelem kx x) . showString "\n"
+      Bin _ kx x l r
+          -> showsTree showelem wide (withBar rbars) (withEmpty rbars) r .
+             showWide wide rbars .
+             showsBars lbars . showString (showelem kx x) . showString "\n" .
+             showWide wide lbars .
+             showsTree showelem wide (withEmpty lbars) (withBar lbars) l
+
+showsTreeHang :: (k -> a -> String) -> Bool -> [String] -> Map k a -> ShowS
+showsTreeHang showelem wide bars t
+  = case t of
+      Tip -> showsBars bars . showString "|\n"
+      Bin _ kx x Tip Tip
+          -> showsBars bars . showString (showelem kx x) . showString "\n"
+      Bin _ kx x l r
+          -> showsBars bars . showString (showelem kx x) . showString "\n" .
+             showWide wide bars .
+             showsTreeHang showelem wide (withBar bars) l .
+             showWide wide bars .
+             showsTreeHang showelem wide (withEmpty bars) r
+
+showWide :: Bool -> [String] -> String -> String
+showWide wide bars
+  | wide      = showString (concat (reverse bars)) . showString "|\n"
+  | otherwise = id
+
+showsBars :: [String] -> ShowS
+showsBars bars
+  = case bars of
+      [] -> id
+      _  -> showString (concat (reverse (tail bars))) . showString node
+
+node :: String
+node           = "+--"
+
+withBar, withEmpty :: [String] -> [String]
+withBar bars   = "|  ":bars
+withEmpty bars = "   ":bars
+
+{--------------------------------------------------------------------
+  Typeable
+--------------------------------------------------------------------}
+
+#include "Typeable.h"
+INSTANCE_TYPEABLE2(Map,mapTc,"Map")
+
+{--------------------------------------------------------------------
+  Assertions
+--------------------------------------------------------------------}
+-- | /O(n)/. Test if the internal map structure is valid.
+--
+-- > valid (fromAscList [(3,"b"), (5,"a")]) == True
+-- > valid (fromAscList [(5,"a"), (3,"b")]) == False
+
+valid :: Ord k => Map k a -> Bool
+valid t
+  = balanced t && ordered t && validsize t
+
+ordered :: Ord a => Map a b -> Bool
+ordered t
+  = bounded (const True) (const True) t
+  where
+    bounded lo hi t'
+      = case t' of
+          Tip              -> True
+          Bin _ kx _ l r  -> (lo kx) && (hi kx) && bounded lo (<kx) l && bounded (>kx) hi r
+
+-- | Exported only for "Debug.QuickCheck"
+balanced :: Map k a -> Bool
+balanced t
+  = case t of
+      Tip            -> True
+      Bin _ _ _ l r  -> (size l + size r <= 1 || (size l <= delta*size r && size r <= delta*size l)) &&
+                        balanced l && balanced r
+
+validsize :: Map a b -> Bool
+validsize t
+  = (realsize t == Just (size t))
+  where
+    realsize t'
+      = case t' of
+          Tip            -> Just 0
+          Bin sz _ _ l r -> case (realsize l,realsize r) of
+                            (Just n,Just m)  | n+m+1 == sz  -> Just sz
+                            _                               -> Nothing
+
+{--------------------------------------------------------------------
+  Utilities
+--------------------------------------------------------------------}
+foldlStrict :: (a -> b -> a) -> a -> [b] -> a
+foldlStrict f = go
+  where
+    go z []     = z
+    go z (x:xs) = let z' = f z x in z' `seq` go z' xs
+{-# INLINE foldlStrict #-}
+
+
+-- | /O(1)/.  Decompose a map into pieces based on the structure of the underlying
+-- tree.  This function is useful for consuming a map in parallel.
+--
+-- No guarantee is made as to the sizes of the pieces; an internal, but
+-- deterministic process determines this.  However, it is guaranteed that the pieces
+-- returned will be in ascending order (all elements in the first submap less than all
+-- elements in the second, and so on).
+--
+-- Examples:
+--
+-- > splitRoot (fromList (zip [1..6] ['a'..])) ==
+-- >   [fromList [(1,'a'),(2,'b'),(3,'c')],fromList [(4,'d')],fromList [(5,'e'),(6,'f')]]
+--
+-- > splitRoot empty == []
+--
+--  Note that the current implementation does not return more than three submaps,
+--  but you should not depend on this behaviour because it can change in the
+--  future without notice.
+splitRoot :: Map k b -> [Map k b]
+splitRoot orig =
+  case orig of
+    Tip           -> []
+    Bin _ k v l r -> [l, singleton k v, r]
+{-# INLINE splitRoot #-}
diff --git a/Data/Map/Lazy.hs b/Data/Map/Lazy.hs
new file mode 100644
--- /dev/null
+++ b/Data/Map/Lazy.hs
@@ -0,0 +1,230 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Safe #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Map.Lazy
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of ordered maps from keys to values
+-- (dictionaries).
+--
+-- API of this module is strict in the keys, but lazy in the values.
+-- If you need value-strict maps, use "Data.Map.Strict" instead.
+-- The 'Map' type itself is shared between the lazy and strict modules,
+-- meaning that the same 'Map' value can be passed to functions in
+-- both modules (although that is rarely needed).
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import qualified Data.Map.Lazy as Map
+--
+-- The implementation of 'Map' is based on /size balanced/ binary trees (or
+-- trees of /bounded balance/) as described by:
+--
+--    * Stephen Adams, \"/Efficient sets: a balancing act/\",
+--     Journal of Functional Programming 3(4):553-562, October 1993,
+--     <http://www.swiss.ai.mit.edu/~adams/BB/>.
+--
+--    * J. Nievergelt and E.M. Reingold,
+--      \"/Binary search trees of bounded balance/\",
+--      SIAM journal of computing 2(1), March 1973.
+--
+-- Note that the implementation is /left-biased/ -- the elements of a
+-- first argument are always preferred to the second, for example in
+-- 'union' or 'insert'.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation (<http://en.wikipedia.org/wiki/Big_O_notation>).
+-----------------------------------------------------------------------------
+
+module Data.Map.Lazy (
+    -- * Strictness properties
+    -- $strictness
+
+    -- * Map type
+#if !defined(TESTING)
+    Map              -- instance Eq,Show,Read
+#else
+    Map(..)          -- instance Eq,Show,Read
+#endif
+
+    -- * Operators
+    , (!), (\\)
+
+    -- * Query
+    , M.null
+    , size
+    , member
+    , notMember
+    , M.lookup
+    , findWithDefault
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+
+    -- * Construction
+    , empty
+    , singleton
+
+    -- ** Insertion
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+
+    -- ** Delete\/Update
+    , delete
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+
+    -- * Combine
+
+    -- ** Union
+    , union
+    , unionWith
+    , unionWithKey
+    , unions
+    , unionsWith
+
+    -- ** Difference
+    , difference
+    , differenceWith
+    , differenceWithKey
+
+    -- ** Intersection
+    , intersection
+    , intersectionWith
+    , intersectionWithKey
+
+    -- ** Universal combining function
+    , mergeWithKey
+
+    -- * Traversal
+    -- ** Map
+    , M.map
+    , mapWithKey
+    , traverseWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeys
+    , mapKeysWith
+    , mapKeysMonotonic
+
+    -- * Folds
+    , M.foldr
+    , M.foldl
+    , foldrWithKey
+    , foldlWithKey
+    , foldMapWithKey
+
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    , foldrWithKey'
+    , foldlWithKey'
+
+    -- * Conversion
+    , elems
+    , keys
+    , assocs
+    , keysSet
+    , fromSet
+
+    -- ** Lists
+    , toList
+    , fromList
+    , fromListWith
+    , fromListWithKey
+
+    -- ** Ordered lists
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+
+    -- * Filter
+    , M.filter
+    , filterWithKey
+    , partition
+    , partitionWithKey
+
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+
+    , split
+    , splitLookup
+    , splitRoot
+
+    -- * Submap
+    , isSubmapOf, isSubmapOfBy
+    , isProperSubmapOf, isProperSubmapOfBy
+
+    -- * Indexed
+    , lookupIndex
+    , findIndex
+    , elemAt
+    , updateAt
+    , deleteAt
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    , minView
+    , maxView
+    , minViewWithKey
+    , maxViewWithKey
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+    , valid
+
+#if defined(TESTING)
+    -- * Internals
+    , bin
+    , balanced
+    , link
+    , merge
+#endif
+
+    ) where
+
+import Data.Map.Base as M
+
+-- $strictness
+--
+-- This module satisfies the following strictness property:
+--
+-- * Key arguments are evaluated to WHNF
+--
+-- Here are some examples that illustrate the property:
+--
+-- > insertWith (\ new old -> old) undefined v m  ==  undefined
+-- > insertWith (\ new old -> old) k undefined m  ==  OK
+-- > delete undefined m  ==  undefined
diff --git a/Data/Map/Strict.hs b/Data/Map/Strict.hs
new file mode 100644
--- /dev/null
+++ b/Data/Map/Strict.hs
@@ -0,0 +1,1182 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Safe #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Map.Strict
+-- Copyright   :  (c) Daan Leijen 2002
+--                (c) Andriy Palamarchuk 2008
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of ordered maps from keys to values
+-- (dictionaries).
+--
+-- API of this module is strict in both the keys and the values.
+-- If you need value-lazy maps, use "Data.Map.Lazy" instead.
+-- The 'Map' type is shared between the lazy and strict modules,
+-- meaning that the same 'Map' value can be passed to functions in
+-- both modules (although that is rarely needed).
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import qualified Data.Map.Strict as Map
+--
+-- The implementation of 'Map' is based on /size balanced/ binary trees (or
+-- trees of /bounded balance/) as described by:
+--
+--    * Stephen Adams, \"/Efficient sets: a balancing act/\",
+--     Journal of Functional Programming 3(4):553-562, October 1993,
+--     <http://www.swiss.ai.mit.edu/~adams/BB/>.
+--
+--    * J. Nievergelt and E.M. Reingold,
+--      \"/Binary search trees of bounded balance/\",
+--      SIAM journal of computing 2(1), March 1973.
+--
+-- Note that the implementation is /left-biased/ -- the elements of a
+-- first argument are always preferred to the second, for example in
+-- 'union' or 'insert'.
+--
+-- Operation comments contain the operation time complexity in
+-- the Big-O notation (<http://en.wikipedia.org/wiki/Big_O_notation>).
+--
+-- Be aware that the 'Functor', 'Traversable' and 'Data' instances
+-- are the same as for the "Data.Map.Lazy" module, so if they are used
+-- on strict maps, the resulting maps will be lazy.
+-----------------------------------------------------------------------------
+
+-- See the notes at the beginning of Data.Map.Base.
+
+module Data.Map.Strict
+    (
+    -- * Strictness properties
+    -- $strictness
+
+    -- * Map type
+#if !defined(TESTING)
+    Map              -- instance Eq,Show,Read
+#else
+    Map(..)          -- instance Eq,Show,Read
+#endif
+
+    -- * Operators
+    , (!), (\\)
+
+    -- * Query
+    , null
+    , size
+    , member
+    , notMember
+    , lookup
+    , findWithDefault
+    , lookupLT
+    , lookupGT
+    , lookupLE
+    , lookupGE
+
+    -- * Construction
+    , empty
+    , singleton
+
+    -- ** Insertion
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+
+    -- ** Delete\/Update
+    , delete
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+
+    -- * Combine
+
+    -- ** Union
+    , union
+    , unionWith
+    , unionWithKey
+    , unions
+    , unionsWith
+
+    -- ** Difference
+    , difference
+    , differenceWith
+    , differenceWithKey
+
+    -- ** Intersection
+    , intersection
+    , intersectionWith
+    , intersectionWithKey
+
+    -- ** Universal combining function
+    , mergeWithKey
+
+    -- * Traversal
+    -- ** Map
+    , map
+    , mapWithKey
+    , traverseWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeys
+    , mapKeysWith
+    , mapKeysMonotonic
+
+    -- * Folds
+    , foldr
+    , foldl
+    , foldrWithKey
+    , foldlWithKey
+    , foldMapWithKey
+
+    -- ** Strict folds
+    , foldr'
+    , foldl'
+    , foldrWithKey'
+    , foldlWithKey'
+
+    -- * Conversion
+    , elems
+    , keys
+    , assocs
+    , keysSet
+    , fromSet
+
+    -- ** Lists
+    , toList
+    , fromList
+    , fromListWith
+    , fromListWithKey
+
+    -- ** Ordered lists
+    , toAscList
+    , toDescList
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+
+    -- * Filter
+    , filter
+    , filterWithKey
+    , partition
+    , partitionWithKey
+
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+
+    , split
+    , splitLookup
+    , splitRoot
+
+    -- * Submap
+    , isSubmapOf, isSubmapOfBy
+    , isProperSubmapOf, isProperSubmapOfBy
+
+    -- * Indexed
+    , lookupIndex
+    , findIndex
+    , elemAt
+    , updateAt
+    , deleteAt
+
+    -- * Min\/Max
+    , findMin
+    , findMax
+    , deleteMin
+    , deleteMax
+    , deleteFindMin
+    , deleteFindMax
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    , minView
+    , maxView
+    , minViewWithKey
+    , maxViewWithKey
+
+    -- * Debugging
+    , showTree
+    , showTreeWith
+    , valid
+
+#if defined(TESTING)
+    -- * Internals
+    , bin
+    , balanced
+    , link
+    , merge
+#endif
+    ) where
+
+import Prelude hiding (lookup,map,filter,foldr,foldl,null)
+
+import Data.Map.Base hiding
+    ( findWithDefault
+    , singleton
+    , insert
+    , insertWith
+    , insertWithKey
+    , insertLookupWithKey
+    , adjust
+    , adjustWithKey
+    , update
+    , updateWithKey
+    , updateLookupWithKey
+    , alter
+    , unionWith
+    , unionWithKey
+    , unionsWith
+    , differenceWith
+    , differenceWithKey
+    , intersectionWith
+    , intersectionWithKey
+    , mergeWithKey
+    , map
+    , mapWithKey
+    , mapAccum
+    , mapAccumWithKey
+    , mapAccumRWithKey
+    , mapKeysWith
+    , fromSet
+    , fromList
+    , fromListWith
+    , fromListWithKey
+    , fromAscList
+    , fromAscListWith
+    , fromAscListWithKey
+    , fromDistinctAscList
+    , mapMaybe
+    , mapMaybeWithKey
+    , mapEither
+    , mapEitherWithKey
+    , updateAt
+    , updateMin
+    , updateMax
+    , updateMinWithKey
+    , updateMaxWithKey
+    )
+import qualified Data.Set.Base as Set
+import Data.StrictPair
+import Data.Bits (shiftL, shiftR)
+
+-- Use macros to define strictness of functions.  STRICT_x_OF_y
+-- denotes an y-ary function strict in the x-th parameter. Similarly
+-- STRICT_x_y_OF_z denotes an z-ary function strict in the x-th and
+-- y-th parameter.  We do not use BangPatterns, because they are not
+-- in any standard and we want the compilers to be compiled by as many
+-- compilers as possible.
+#define STRICT_1_OF_2(fn) fn arg _ | arg `seq` False = undefined
+#define STRICT_1_OF_3(fn) fn arg _ _ | arg `seq` False = undefined
+#define STRICT_2_OF_3(fn) fn _ arg _ | arg `seq` False = undefined
+#define STRICT_1_2_OF_3(fn) fn arg1 arg2 _ | arg1 `seq` arg2 `seq` False = undefined
+#define STRICT_2_OF_4(fn) fn _ arg _ _ | arg `seq` False = undefined
+
+-- $strictness
+--
+-- This module satisfies the following strictness properties:
+--
+-- 1. Key arguments are evaluated to WHNF;
+--
+-- 2. Keys and values are evaluated to WHNF before they are stored in
+--    the map.
+--
+-- Here's an example illustrating the first property:
+--
+-- > delete undefined m  ==  undefined
+--
+-- Here are some examples that illustrate the second property:
+--
+-- > map (\ v -> undefined) m  ==  undefined      -- m is not empty
+-- > mapKeys (\ k -> undefined) m  ==  undefined  -- m is not empty
+
+{--------------------------------------------------------------------
+  Query
+--------------------------------------------------------------------}
+
+-- | /O(log n)/. The expression @('findWithDefault' def k map)@ returns
+-- the value at key @k@ or returns default value @def@
+-- when the key is not in the map.
+--
+-- > findWithDefault 'x' 1 (fromList [(5,'a'), (3,'b')]) == 'x'
+-- > findWithDefault 'x' 5 (fromList [(5,'a'), (3,'b')]) == 'a'
+
+-- See Map.Base.Note: Local 'go' functions and capturing
+findWithDefault :: Ord k => a -> k -> Map k a -> a
+findWithDefault def k = k `seq` go
+  where
+    go Tip = def
+    go (Bin _ kx x l r) = case compare k kx of
+      LT -> go l
+      GT -> go r
+      EQ -> x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE findWithDefault #-}
+#else
+{-# INLINE findWithDefault #-}
+#endif
+
+{--------------------------------------------------------------------
+  Construction
+--------------------------------------------------------------------}
+
+-- | /O(1)/. A map with a single element.
+--
+-- > singleton 1 'a'        == fromList [(1, 'a')]
+-- > size (singleton 1 'a') == 1
+
+singleton :: k -> a -> Map k a
+singleton k x = x `seq` Bin 1 k x Tip Tip
+{-# INLINE singleton #-}
+
+{--------------------------------------------------------------------
+  Insertion
+--------------------------------------------------------------------}
+-- | /O(log n)/. Insert a new key and value in the map.
+-- If the key is already present in the map, the associated value is
+-- replaced with the supplied value. 'insert' is equivalent to
+-- @'insertWith' 'const'@.
+--
+-- > insert 5 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'x')]
+-- > insert 7 'x' (fromList [(5,'a'), (3,'b')]) == fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+-- > insert 5 'x' empty                         == singleton 5 'x'
+
+-- See Map.Base.Note: Type of local 'go' function
+insert :: Ord k => k -> a -> Map k a -> Map k a
+insert = go
+  where
+    go :: Ord k => k -> a -> Map k a -> Map k a
+    STRICT_1_2_OF_3(go)
+    go kx x Tip = singleton kx x
+    go kx x (Bin sz ky y l r) =
+        case compare kx ky of
+            LT -> balanceL ky y (go kx x l) r
+            GT -> balanceR ky y l (go kx x r)
+            EQ -> Bin sz kx x l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insert #-}
+#else
+{-# INLINE insert #-}
+#endif
+
+-- | /O(log n)/. Insert with a function, combining new value and old value.
+-- @'insertWith' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert the pair @(key, f new_value old_value)@.
+--
+-- > insertWith (++) 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "xxxa")]
+-- > insertWith (++) 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWith (++) 5 "xxx" empty                         == singleton 5 "xxx"
+
+insertWith :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWith f = insertWithKey (\_ x' y' -> f x' y')
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertWith #-}
+#else
+{-# INLINE insertWith #-}
+#endif
+
+-- | /O(log n)/. Insert with a function, combining key, new value and old value.
+-- @'insertWithKey' f key value mp@
+-- will insert the pair (key, value) into @mp@ if key does
+-- not exist in the map. If the key does exist, the function will
+-- insert the pair @(key,f key new_value old_value)@.
+-- Note that the key passed to f is the same key passed to 'insertWithKey'.
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:xxx|a")]
+-- > insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "xxx")]
+-- > insertWithKey f 5 "xxx" empty                         == singleton 5 "xxx"
+
+-- See Map.Base.Note: Type of local 'go' function
+insertWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+insertWithKey = go
+  where
+    go :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
+    STRICT_2_OF_4(go)
+    go _ kx x Tip = singleton kx x
+    go f kx x (Bin sy ky y l r) =
+        case compare kx ky of
+            LT -> balanceL ky y (go f kx x l) r
+            GT -> balanceR ky y l (go f kx x r)
+            EQ -> let x' = f kx x y
+                  in x' `seq` Bin sy kx x' l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertWithKey #-}
+#else
+{-# INLINE insertWithKey #-}
+#endif
+
+-- | /O(log n)/. Combines insert operation with old value retrieval.
+-- The expression (@'insertLookupWithKey' f k x map@)
+-- is a pair where the first element is equal to (@'lookup' k map@)
+-- and the second element equal to (@'insertWithKey' f k x map@).
+--
+-- > let f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+-- > insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "5:xxx|a")])
+-- > insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "xxx")])
+-- > insertLookupWithKey f 5 "xxx" empty                         == (Nothing,  singleton 5 "xxx")
+--
+-- This is how to define @insertLookup@ using @insertLookupWithKey@:
+--
+-- > let insertLookup kx x t = insertLookupWithKey (\_ a _ -> a) kx x t
+-- > insertLookup 5 "x" (fromList [(5,"a"), (3,"b")]) == (Just "a", fromList [(3, "b"), (5, "x")])
+-- > insertLookup 7 "x" (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a"), (7, "x")])
+
+-- See Map.Base.Note: Type of local 'go' function
+insertLookupWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a
+                    -> (Maybe a, Map k a)
+insertLookupWithKey f0 kx0 x0 t0 = toPair $ go f0 kx0 x0 t0
+  where
+    go :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> StrictPair (Maybe a) (Map k a)
+    STRICT_2_OF_4(go)
+    go _ kx x Tip = Nothing :*: singleton kx x
+    go f kx x (Bin sy ky y l r) =
+        case compare kx ky of
+            LT -> let (found :*: l') = go f kx x l
+                  in found :*: balanceL ky y l' r
+            GT -> let (found :*: r') = go f kx x r
+                  in found :*: balanceR ky y l r'
+            EQ -> let x' = f kx x y
+                  in x' `seq` (Just y :*: Bin sy kx x' l r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertLookupWithKey #-}
+#else
+{-# INLINE insertLookupWithKey #-}
+#endif
+
+{--------------------------------------------------------------------
+  Deletion
+--------------------------------------------------------------------}
+
+-- | /O(log n)/. Update a value at a specific key with the result of the provided function.
+-- When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjust ("new " ++) 7 empty                         == empty
+
+adjust :: Ord k => (a -> a) -> k -> Map k a -> Map k a
+adjust f = adjustWithKey (\_ x -> f x)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE adjust #-}
+#else
+{-# INLINE adjust #-}
+#endif
+
+-- | /O(log n)/. Adjust a value at a specific key. When the key is not
+-- a member of the map, the original map is returned.
+--
+-- > let f key x = (show key) ++ ":new " ++ x
+-- > adjustWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > adjustWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > adjustWithKey f 7 empty                         == empty
+
+adjustWithKey :: Ord k => (k -> a -> a) -> k -> Map k a -> Map k a
+adjustWithKey f = updateWithKey (\k' x' -> Just (f k' x'))
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE adjustWithKey #-}
+#else
+{-# INLINE adjustWithKey #-}
+#endif
+
+-- | /O(log n)/. The expression (@'update' f k map@) updates the value @x@
+-- at @k@ (if it is in the map). If (@f x@) is 'Nothing', the element is
+-- deleted. If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > update f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "new a")]
+-- > update f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > update f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+update :: Ord k => (a -> Maybe a) -> k -> Map k a -> Map k a
+update f = updateWithKey (\_ x -> f x)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE update #-}
+#else
+{-# INLINE update #-}
+#endif
+
+-- | /O(log n)/. The expression (@'updateWithKey' f k map@) updates the
+-- value @x@ at @k@ (if it is in the map). If (@f k x@) is 'Nothing',
+-- the element is deleted. If it is (@'Just' y@), the key @k@ is bound
+-- to the new value @y@.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateWithKey f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "5:new a")]
+-- > updateWithKey f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > updateWithKey f 3 (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+-- See Map.Base.Note: Type of local 'go' function
+updateWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> Map k a
+updateWithKey = go
+  where
+    go :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> Map k a
+    STRICT_2_OF_3(go)
+    go _ _ Tip = Tip
+    go f k(Bin sx kx x l r) =
+        case compare k kx of
+           LT -> balanceR kx x (go f k l) r
+           GT -> balanceL kx x l (go f k r)
+           EQ -> case f kx x of
+                   Just x' -> x' `seq` Bin sx kx x' l r
+                   Nothing -> glue l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE updateWithKey #-}
+#else
+{-# INLINE updateWithKey #-}
+#endif
+
+-- | /O(log n)/. Lookup and update. See also 'updateWithKey'.
+-- The function returns changed value, if it is updated.
+-- Returns the original key value if the map entry is deleted.
+--
+-- > let f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+-- > updateLookupWithKey f 5 (fromList [(5,"a"), (3,"b")]) == (Just "5:new a", fromList [(3, "b"), (5, "5:new a")])
+-- > updateLookupWithKey f 7 (fromList [(5,"a"), (3,"b")]) == (Nothing,  fromList [(3, "b"), (5, "a")])
+-- > updateLookupWithKey f 3 (fromList [(5,"a"), (3,"b")]) == (Just "b", singleton 5 "a")
+
+-- See Map.Base.Note: Type of local 'go' function
+updateLookupWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> (Maybe a,Map k a)
+updateLookupWithKey f0 k0 t0 = toPair $ go f0 k0 t0
+ where
+   go :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> StrictPair (Maybe a) (Map k a)
+   STRICT_2_OF_3(go)
+   go _ _ Tip = (Nothing :*: Tip)
+   go f k (Bin sx kx x l r) =
+          case compare k kx of
+               LT -> let (found :*: l') = go f k l
+                     in found :*: balanceR kx x l' r
+               GT -> let (found :*: r') = go f k r
+                     in found :*: balanceL kx x l r'
+               EQ -> case f kx x of
+                       Just x' -> x' `seq` (Just x' :*: Bin sx kx x' l r)
+                       Nothing -> (Just x :*: glue l r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE updateLookupWithKey #-}
+#else
+{-# INLINE updateLookupWithKey #-}
+#endif
+
+-- | /O(log n)/. The expression (@'alter' f k map@) alters the value @x@ at @k@, or absence thereof.
+-- 'alter' can be used to insert, delete, or update a value in a 'Map'.
+-- In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.
+--
+-- > let f _ = Nothing
+-- > alter f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a")]
+-- > alter f 5 (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- >
+-- > let f _ = Just "c"
+-- > alter f 7 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "a"), (7, "c")]
+-- > alter f 5 (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "c")]
+
+-- See Map.Base.Note: Type of local 'go' function
+alter :: Ord k => (Maybe a -> Maybe a) -> k -> Map k a -> Map k a
+alter = go
+  where
+    go :: Ord k => (Maybe a -> Maybe a) -> k -> Map k a -> Map k a
+    STRICT_2_OF_3(go)
+    go f k Tip = case f Nothing of
+               Nothing -> Tip
+               Just x  -> singleton k x
+
+    go f k (Bin sx kx x l r) = case compare k kx of
+               LT -> balance kx x (go f k l) r
+               GT -> balance kx x l (go f k r)
+               EQ -> case f (Just x) of
+                       Just x' -> x' `seq` Bin sx kx x' l r
+                       Nothing -> glue l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE alter #-}
+#else
+{-# INLINE alter #-}
+#endif
+
+{--------------------------------------------------------------------
+  Indexing
+--------------------------------------------------------------------}
+
+-- | /O(log n)/. Update the element at /index/. Calls 'error' when an
+-- invalid index is used.
+--
+-- > updateAt (\ _ _ -> Just "x") 0    (fromList [(5,"a"), (3,"b")]) == fromList [(3, "x"), (5, "a")]
+-- > updateAt (\ _ _ -> Just "x") 1    (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "x")]
+-- > updateAt (\ _ _ -> Just "x") 2    (fromList [(5,"a"), (3,"b")])    Error: index out of range
+-- > updateAt (\ _ _ -> Just "x") (-1) (fromList [(5,"a"), (3,"b")])    Error: index out of range
+-- > updateAt (\_ _  -> Nothing)  0    (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+-- > updateAt (\_ _  -> Nothing)  1    (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+-- > updateAt (\_ _  -> Nothing)  2    (fromList [(5,"a"), (3,"b")])    Error: index out of range
+-- > updateAt (\_ _  -> Nothing)  (-1) (fromList [(5,"a"), (3,"b")])    Error: index out of range
+
+updateAt :: (k -> a -> Maybe a) -> Int -> Map k a -> Map k a
+updateAt f i t = i `seq`
+  case t of
+    Tip -> error "Map.updateAt: index out of range"
+    Bin sx kx x l r -> case compare i sizeL of
+      LT -> balanceR kx x (updateAt f i l) r
+      GT -> balanceL kx x l (updateAt f (i-sizeL-1) r)
+      EQ -> case f kx x of
+              Just x' -> x' `seq` Bin sx kx x' l r
+              Nothing -> glue l r
+      where
+        sizeL = size l
+
+{--------------------------------------------------------------------
+  Minimal, Maximal
+--------------------------------------------------------------------}
+
+-- | /O(log n)/. Update the value at the minimal key.
+--
+-- > updateMin (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "Xb"), (5, "a")]
+-- > updateMin (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMin :: (a -> Maybe a) -> Map k a -> Map k a
+updateMin f m
+  = updateMinWithKey (\_ x -> f x) m
+
+-- | /O(log n)/. Update the value at the maximal key.
+--
+-- > updateMax (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3, "b"), (5, "Xa")]
+-- > updateMax (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMax :: (a -> Maybe a) -> Map k a -> Map k a
+updateMax f m
+  = updateMaxWithKey (\_ x -> f x) m
+
+
+-- | /O(log n)/. Update the value at the minimal key.
+--
+-- > updateMinWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"3:b"), (5,"a")]
+-- > updateMinWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"
+
+updateMinWithKey :: (k -> a -> Maybe a) -> Map k a -> Map k a
+updateMinWithKey _ Tip                 = Tip
+updateMinWithKey f (Bin sx kx x Tip r) = case f kx x of
+                                           Nothing -> r
+                                           Just x' -> x' `seq` Bin sx kx x' Tip r
+updateMinWithKey f (Bin _ kx x l r)    = balanceR kx x (updateMinWithKey f l) r
+
+-- | /O(log n)/. Update the value at the maximal key.
+--
+-- > updateMaxWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) == fromList [(3,"b"), (5,"5:a")]
+-- > updateMaxWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
+
+updateMaxWithKey :: (k -> a -> Maybe a) -> Map k a -> Map k a
+updateMaxWithKey _ Tip                 = Tip
+updateMaxWithKey f (Bin sx kx x l Tip) = case f kx x of
+                                           Nothing -> l
+                                           Just x' -> x' `seq` Bin sx kx x' l Tip
+updateMaxWithKey f (Bin _ kx x l r)    = balanceL kx x l (updateMaxWithKey f r)
+
+{--------------------------------------------------------------------
+  Union.
+--------------------------------------------------------------------}
+
+-- | The union of a list of maps, with a combining operation:
+--   (@'unionsWith' f == 'Prelude.foldl' ('unionWith' f) 'empty'@).
+--
+-- > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+-- >     == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
+
+unionsWith :: Ord k => (a->a->a) -> [Map k a] -> Map k a
+unionsWith f ts
+  = foldlStrict (unionWith f) empty ts
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unionsWith #-}
+#endif
+
+{--------------------------------------------------------------------
+  Union with a combining function
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Union with a combining function. The implementation uses the efficient /hedge-union/ algorithm.
+--
+-- > unionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "aA"), (7, "C")]
+
+unionWith :: Ord k => (a -> a -> a) -> Map k a -> Map k a -> Map k a
+unionWith f m1 m2
+  = unionWithKey (\_ x y -> f x y) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unionWith #-}
+#endif
+
+-- | /O(n+m)/.
+-- Union with a combining function. The implementation uses the efficient /hedge-union/ algorithm.
+--
+-- > let f key left_value right_value = (show key) ++ ":" ++ left_value ++ "|" ++ right_value
+-- > unionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == fromList [(3, "b"), (5, "5:a|A"), (7, "C")]
+
+unionWithKey :: Ord k => (k -> a -> a -> a) -> Map k a -> Map k a -> Map k a
+unionWithKey f t1 t2 = mergeWithKey (\k x1 x2 -> Just $ f k x1 x2) id id t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unionWithKey #-}
+#endif
+
+{--------------------------------------------------------------------
+  Difference
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. Difference with a combining function.
+-- When two equal keys are
+-- encountered, the combining function is applied to the values of these keys.
+-- If it returns 'Nothing', the element is discarded (proper set difference). If
+-- it returns (@'Just' y@), the element is updated with a new value @y@.
+-- The implementation uses an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > let f al ar = if al == "b" then Just (al ++ ":" ++ ar) else Nothing
+-- > differenceWith f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (7, "C")])
+-- >     == singleton 3 "b:B"
+
+differenceWith :: Ord k => (a -> b -> Maybe a) -> Map k a -> Map k b -> Map k a
+differenceWith f m1 m2
+  = differenceWithKey (\_ x y -> f x y) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE differenceWith #-}
+#endif
+
+-- | /O(n+m)/. Difference with a combining function. When two equal keys are
+-- encountered, the combining function is applied to the key and both values.
+-- If it returns 'Nothing', the element is discarded (proper set difference). If
+-- it returns (@'Just' y@), the element is updated with a new value @y@.
+-- The implementation uses an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > let f k al ar = if al == "b" then Just ((show k) ++ ":" ++ al ++ "|" ++ ar) else Nothing
+-- > differenceWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (10, "C")])
+-- >     == singleton 3 "3:b|B"
+
+differenceWithKey :: Ord k => (k -> a -> b -> Maybe a) -> Map k a -> Map k b -> Map k a
+differenceWithKey f t1 t2 = mergeWithKey f id (const Tip) t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE differenceWithKey #-}
+#endif
+
+
+{--------------------------------------------------------------------
+  Intersection
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. Intersection with a combining function.  The implementation uses
+-- an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > intersectionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "aA"
+
+intersectionWith :: Ord k => (a -> b -> c) -> Map k a -> Map k b -> Map k c
+intersectionWith f m1 m2
+  = intersectionWithKey (\_ x y -> f x y) m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE intersectionWith #-}
+#endif
+
+-- | /O(n+m)/. Intersection with a combining function.  The implementation uses
+-- an efficient /hedge/ algorithm comparable with /hedge-union/.
+--
+-- > let f k al ar = (show k) ++ ":" ++ al ++ "|" ++ ar
+-- > intersectionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) == singleton 5 "5:a|A"
+
+
+intersectionWithKey :: Ord k => (k -> a -> b -> c) -> Map k a -> Map k b -> Map k c
+intersectionWithKey f t1 t2 = mergeWithKey (\k x1 x2 -> Just $ f k x1 x2) (const Tip) (const Tip) t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE intersectionWithKey #-}
+#endif
+
+
+{--------------------------------------------------------------------
+  MergeWithKey
+--------------------------------------------------------------------}
+
+-- | /O(n+m)/. A high-performance universal combining function. This function
+-- is used to define 'unionWith', 'unionWithKey', 'differenceWith',
+-- 'differenceWithKey', 'intersectionWith', 'intersectionWithKey' and can be
+-- used to define other custom combine functions.
+--
+-- Please make sure you know what is going on when using 'mergeWithKey',
+-- otherwise you can be surprised by unexpected code growth or even
+-- corruption of the data structure.
+--
+-- When 'mergeWithKey' is given three arguments, it is inlined to the call
+-- site. You should therefore use 'mergeWithKey' only to define your custom
+-- combining functions. For example, you could define 'unionWithKey',
+-- 'differenceWithKey' and 'intersectionWithKey' as
+--
+-- > myUnionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) id id m1 m2
+-- > myDifferenceWithKey f m1 m2 = mergeWithKey f id (const empty) m1 m2
+-- > myIntersectionWithKey f m1 m2 = mergeWithKey (\k x1 x2 -> Just (f k x1 x2)) (const empty) (const empty) m1 m2
+--
+-- When calling @'mergeWithKey' combine only1 only2@, a function combining two
+-- 'IntMap's is created, such that
+--
+-- * if a key is present in both maps, it is passed with both corresponding
+--   values to the @combine@ function. Depending on the result, the key is either
+--   present in the result with specified value, or is left out;
+--
+-- * a nonempty subtree present only in the first map is passed to @only1@ and
+--   the output is added to the result;
+--
+-- * a nonempty subtree present only in the second map is passed to @only2@ and
+--   the output is added to the result.
+--
+-- The @only1@ and @only2@ methods /must return a map with a subset (possibly empty) of the keys of the given map/.
+-- The values can be modified arbitrarily. Most common variants of @only1@ and
+-- @only2@ are 'id' and @'const' 'empty'@, but for example @'map' f@ or
+-- @'filterWithKey' f@ could be used for any @f@.
+
+mergeWithKey :: Ord k => (k -> a -> b -> Maybe c) -> (Map k a -> Map k c) -> (Map k b -> Map k c)
+             -> Map k a -> Map k b -> Map k c
+mergeWithKey f g1 g2 = go
+  where
+    go Tip t2 = g2 t2
+    go t1 Tip = g1 t1
+    go t1 t2 = hedgeMerge NothingS NothingS t1 t2
+
+    hedgeMerge _   _   t1  Tip = g1 t1
+    hedgeMerge blo bhi Tip (Bin _ kx x l r) = g2 $ link kx x (filterGt blo l) (filterLt bhi r)
+    hedgeMerge blo bhi (Bin _ kx x l r) t2 = let l' = hedgeMerge blo bmi l (trim blo bmi t2)
+                                                 (found, trim_t2) = trimLookupLo kx bhi t2
+                                                 r' = hedgeMerge bmi bhi r trim_t2
+                                             in case found of
+                                                  Nothing -> case g1 (singleton kx x) of
+                                                               Tip -> merge l' r'
+                                                               (Bin _ _ x' Tip Tip) -> link kx x' l' r'
+                                                               _ -> error "mergeWithKey: Given function only1 does not fulfil required conditions (see documentation)"
+                                                  Just x2 -> case f kx x x2 of
+                                                               Nothing -> merge l' r'
+                                                               Just x' -> x' `seq` link kx x' l' r'
+      where bmi = JustS kx
+{-# INLINE mergeWithKey #-}
+
+{--------------------------------------------------------------------
+  Filter and partition
+--------------------------------------------------------------------}
+
+-- | /O(n)/. Map values and collect the 'Just' results.
+--
+-- > let f x = if x == "a" then Just "new a" else Nothing
+-- > mapMaybe f (fromList [(5,"a"), (3,"b")]) == singleton 5 "new a"
+
+mapMaybe :: (a -> Maybe b) -> Map k a -> Map k b
+mapMaybe f = mapMaybeWithKey (\_ x -> f x)
+
+-- | /O(n)/. Map keys\/values and collect the 'Just' results.
+--
+-- > let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
+-- > mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
+
+mapMaybeWithKey :: (k -> a -> Maybe b) -> Map k a -> Map k b
+mapMaybeWithKey _ Tip = Tip
+mapMaybeWithKey f (Bin _ kx x l r) = case f kx x of
+  Just y  -> y `seq` link kx y (mapMaybeWithKey f l) (mapMaybeWithKey f r)
+  Nothing -> merge (mapMaybeWithKey f l) (mapMaybeWithKey f r)
+
+-- | /O(n)/. Map values and separate the 'Left' and 'Right' results.
+--
+-- > let f a = if a < "c" then Left a else Right a
+-- > mapEither f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(3,"b"), (5,"a")], fromList [(1,"x"), (7,"z")])
+-- >
+-- > mapEither (\ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+
+mapEither :: (a -> Either b c) -> Map k a -> (Map k b, Map k c)
+mapEither f m
+  = mapEitherWithKey (\_ x -> f x) m
+
+-- | /O(n)/. Map keys\/values and separate the 'Left' and 'Right' results.
+--
+-- > let f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
+-- > mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])
+-- >
+-- > mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+-- >     == (empty, fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])
+
+mapEitherWithKey :: (k -> a -> Either b c) -> Map k a -> (Map k b, Map k c)
+mapEitherWithKey f0 t0 = toPair $ go f0 t0
+  where
+    go _ Tip = (Tip :*: Tip)
+    go f (Bin _ kx x l r) = case f kx x of
+      Left y  -> y `seq` (link kx y l1 r1 :*: merge l2 r2)
+      Right z -> z `seq` (merge l1 r1 :*: link kx z l2 r2)
+     where
+        (l1 :*: l2) = go f l
+        (r1 :*: r2) = go f r
+
+{--------------------------------------------------------------------
+  Mapping
+--------------------------------------------------------------------}
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > map (++ "x") (fromList [(5,"a"), (3,"b")]) == fromList [(3, "bx"), (5, "ax")]
+
+map :: (a -> b) -> Map k a -> Map k b
+map _ Tip = Tip
+map f (Bin sx kx x l r) = let x' = f x in x' `seq` Bin sx kx x' (map f l) (map f r)
+
+-- | /O(n)/. Map a function over all values in the map.
+--
+-- > let f key x = (show key) ++ ":" ++ x
+-- > mapWithKey f (fromList [(5,"a"), (3,"b")]) == fromList [(3, "3:b"), (5, "5:a")]
+
+mapWithKey :: (k -> a -> b) -> Map k a -> Map k b
+mapWithKey _ Tip = Tip
+mapWithKey f (Bin sx kx x l r) = let x' = f kx x
+                                 in x' `seq` Bin sx kx x' (mapWithKey f l) (mapWithKey f r)
+
+-- | /O(n)/. The function 'mapAccum' threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a b = (a ++ b, b ++ "X")
+-- > mapAccum f "Everything: " (fromList [(5,"a"), (3,"b")]) == ("Everything: ba", fromList [(3, "bX"), (5, "aX")])
+
+mapAccum :: (a -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccum f a m
+  = mapAccumWithKey (\a' _ x' -> f a' x') a m
+
+-- | /O(n)/. The function 'mapAccumWithKey' threads an accumulating
+-- argument through the map in ascending order of keys.
+--
+-- > let f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+-- > mapAccumWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) == ("Everything: 3-b 5-a", fromList [(3, "bX"), (5, "aX")])
+
+mapAccumWithKey :: (a -> k -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccumWithKey f a t
+  = mapAccumL f a t
+
+-- | /O(n)/. The function 'mapAccumL' threads an accumulating
+-- argument through the map in ascending order of keys.
+mapAccumL :: (a -> k -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccumL _ a Tip               = (a,Tip)
+mapAccumL f a (Bin sx kx x l r) =
+  let (a1,l') = mapAccumL f a l
+      (a2,x') = f a1 kx x
+      (a3,r') = mapAccumL f a2 r
+  in x' `seq` (a3,Bin sx kx x' l' r')
+
+-- | /O(n)/. The function 'mapAccumR' threads an accumulating
+-- argument through the map in descending order of keys.
+mapAccumRWithKey :: (a -> k -> b -> (a,c)) -> a -> Map k b -> (a,Map k c)
+mapAccumRWithKey _ a Tip = (a,Tip)
+mapAccumRWithKey f a (Bin sx kx x l r) =
+  let (a1,r') = mapAccumRWithKey f a r
+      (a2,x') = f a1 kx x
+      (a3,l') = mapAccumRWithKey f a2 l
+  in x' `seq` (a3,Bin sx kx x' l' r')
+
+-- | /O(n*log n)/.
+-- @'mapKeysWith' c f s@ is the map obtained by applying @f@ to each key of @s@.
+--
+-- The size of the result may be smaller if @f@ maps two or more distinct
+-- keys to the same new key.  In this case the associated values will be
+-- combined using @c@.
+--
+-- > mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "cdab"
+-- > mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "cdab"
+
+mapKeysWith :: Ord k2 => (a -> a -> a) -> (k1->k2) -> Map k1 a -> Map k2 a
+mapKeysWith c f = fromListWith c . foldrWithKey (\k x xs -> (f k, x) : xs) []
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE mapKeysWith #-}
+#endif
+
+{--------------------------------------------------------------------
+  Conversions
+--------------------------------------------------------------------}
+
+-- | /O(n)/. Build a map from a set of keys and a function which for each key
+-- computes its value.
+--
+-- > fromSet (\k -> replicate k 'a') (Data.Set.fromList [3, 5]) == fromList [(5,"aaaaa"), (3,"aaa")]
+-- > fromSet undefined Data.Set.empty == empty
+
+fromSet :: (k -> a) -> Set.Set k -> Map k a
+fromSet _ Set.Tip = Tip
+fromSet f (Set.Bin sz x l r) = case f x of v -> v `seq` Bin sz x v (fromSet f l) (fromSet f r)
+
+{--------------------------------------------------------------------
+  Lists
+  use [foldlStrict] to reduce demand on the control-stack
+--------------------------------------------------------------------}
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs. See also 'fromAscList'.
+-- If the list contains more than one value for the same key, the last value
+-- for the key is retained.
+--
+-- If the keys of the list are ordered, linear-time implementation is used,
+-- with the performance equal to 'fromDistinctAscList'.
+--
+-- > fromList [] == empty
+-- > fromList [(5,"a"), (3,"b"), (5, "c")] == fromList [(5,"c"), (3,"b")]
+-- > fromList [(5,"c"), (3,"b"), (5, "a")] == fromList [(5,"a"), (3,"b")]
+
+-- For some reason, when 'singleton' is used in fromList or in
+-- create, it is not inlined, so we inline it manually.
+fromList :: Ord k => [(k,a)] -> Map k a
+fromList [] = Tip
+fromList [(kx, x)] = x `seq` Bin 1 kx x Tip Tip
+fromList ((kx0, x0) : xs0) | not_ordered kx0 xs0 = x0 `seq` fromList' (Bin 1 kx0 x0 Tip Tip) xs0
+                           | otherwise = x0 `seq` go (1::Int) (Bin 1 kx0 x0 Tip Tip) xs0
+  where
+    not_ordered _ [] = False
+    not_ordered kx ((ky,_) : _) = kx >= ky
+    {-# INLINE not_ordered #-}
+
+    fromList' t0 xs = foldlStrict ins t0 xs
+      where ins t (k,x) = insert k x t
+
+    STRICT_1_OF_3(go)
+    go _ t [] = t
+    go _ t [(kx, x)] = x `seq` insertMax kx x t
+    go s l xs@((kx, x) : xss) | not_ordered kx xss = fromList' l xs
+                              | otherwise = case create s xss of
+                                  (r, ys, []) -> x `seq` go (s `shiftL` 1) (link kx x l r) ys
+                                  (r, _,  ys) -> x `seq` fromList' (link kx x l r) ys
+
+    -- The create is returning a triple (tree, xs, ys). Both xs and ys
+    -- represent not yet processed elements and only one of them can be nonempty.
+    -- If ys is nonempty, the keys in ys are not ordered with respect to tree
+    -- and must be inserted using fromList'. Otherwise the keys have been
+    -- ordered so far.
+    STRICT_1_OF_2(create)
+    create _ [] = (Tip, [], [])
+    create s xs@(xp : xss)
+      | s == 1 = case xp of (kx, x) | not_ordered kx xss -> x `seq` (Bin 1 kx x Tip Tip, [], xss)
+                                    | otherwise -> x `seq` (Bin 1 kx x Tip Tip, xss, [])
+      | otherwise = case create (s `shiftR` 1) xs of
+                      res@(_, [], _) -> res
+                      (l, [(ky, y)], zs) -> y `seq` (insertMax ky y l, [], zs)
+                      (l, ys@((ky, y):yss), _) | not_ordered ky yss -> (l, [], ys)
+                                               | otherwise -> case create (s `shiftR` 1) yss of
+                                                   (r, zs, ws) -> y `seq` (link ky y l r, zs, ws)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromList #-}
+#endif
+
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs with a combining function. See also 'fromAscListWith'.
+--
+-- > fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] == fromList [(3, "ab"), (5, "aba")]
+-- > fromListWith (++) [] == empty
+
+fromListWith :: Ord k => (a -> a -> a) -> [(k,a)] -> Map k a
+fromListWith f xs
+  = fromListWithKey (\_ x y -> f x y) xs
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromListWith #-}
+#endif
+
+-- | /O(n*log n)/. Build a map from a list of key\/value pairs with a combining function. See also 'fromAscListWithKey'.
+--
+-- > let f k a1 a2 = (show k) ++ a1 ++ a2
+-- > fromListWithKey f [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] == fromList [(3, "3ab"), (5, "5a5ba")]
+-- > fromListWithKey f [] == empty
+
+fromListWithKey :: Ord k => (k -> a -> a -> a) -> [(k,a)] -> Map k a
+fromListWithKey f xs
+  = foldlStrict ins empty xs
+  where
+    ins t (k,x) = insertWithKey f k x t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromListWithKey #-}
+#endif
+
+{--------------------------------------------------------------------
+  Building trees from ascending/descending lists can be done in linear time.
+
+  Note that if [xs] is ascending that:
+    fromAscList xs       == fromList xs
+    fromAscListWith f xs == fromListWith f xs
+--------------------------------------------------------------------}
+-- | /O(n)/. Build a map from an ascending list in linear time.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscList [(3,"b"), (5,"a")]          == fromList [(3, "b"), (5, "a")]
+-- > fromAscList [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "b")]
+-- > valid (fromAscList [(3,"b"), (5,"a"), (5,"b")]) == True
+-- > valid (fromAscList [(5,"a"), (3,"b"), (5,"b")]) == False
+
+fromAscList :: Eq k => [(k,a)] -> Map k a
+fromAscList xs
+  = fromAscListWithKey (\_ x _ -> x) xs
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscList #-}
+#endif
+
+-- | /O(n)/. Build a map from an ascending list in linear time with a combining function for equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] == fromList [(3, "b"), (5, "ba")]
+-- > valid (fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")]) == True
+-- > valid (fromAscListWith (++) [(5,"a"), (3,"b"), (5,"b")]) == False
+
+fromAscListWith :: Eq k => (a -> a -> a) -> [(k,a)] -> Map k a
+fromAscListWith f xs
+  = fromAscListWithKey (\_ x y -> f x y) xs
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscListWith #-}
+#endif
+
+-- | /O(n)/. Build a map from an ascending list in linear time with a
+-- combining function for equal keys.
+-- /The precondition (input list is ascending) is not checked./
+--
+-- > let f k a1 a2 = (show k) ++ ":" ++ a1 ++ a2
+-- > fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")] == fromList [(3, "b"), (5, "5:b5:ba")]
+-- > valid (fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")]) == True
+-- > valid (fromAscListWithKey f [(5,"a"), (3,"b"), (5,"b"), (5,"b")]) == False
+
+fromAscListWithKey :: Eq k => (k -> a -> a -> a) -> [(k,a)] -> Map k a
+fromAscListWithKey f xs
+  = fromDistinctAscList (combineEq f xs)
+  where
+  -- [combineEq f xs] combines equal elements with function [f] in an ordered list [xs]
+  combineEq _ xs'
+    = case xs' of
+        []     -> []
+        [x]    -> [x]
+        (x:xx) -> combineEq' x xx
+
+  combineEq' z [] = [z]
+  combineEq' z@(kz,zz) (x@(kx,xx):xs')
+    | kx==kz    = let yy = f kx xx zz in yy `seq` combineEq' (kx,yy) xs'
+    | otherwise = z:combineEq' x xs'
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscListWithKey #-}
+#endif
+
+-- | /O(n)/. Build a map from an ascending list of distinct elements in linear time.
+-- /The precondition is not checked./
+--
+-- > fromDistinctAscList [(3,"b"), (5,"a")] == fromList [(3, "b"), (5, "a")]
+-- > valid (fromDistinctAscList [(3,"b"), (5,"a")])          == True
+-- > valid (fromDistinctAscList [(3,"b"), (5,"a"), (5,"b")]) == False
+
+-- For some reason, when 'singleton' is used in fromDistinctAscList or in
+-- create, it is not inlined, so we inline it manually.
+fromDistinctAscList :: [(k,a)] -> Map k a
+fromDistinctAscList [] = Tip
+fromDistinctAscList ((kx0, x0) : xs0) = x0 `seq` go (1::Int) (Bin 1 kx0 x0 Tip Tip) xs0
+  where
+    STRICT_1_OF_3(go)
+    go _ t [] = t
+    go s l ((kx, x) : xs) = case create s xs of
+                              (r, ys) -> x `seq` go (s `shiftL` 1) (link kx x l r) ys
+
+    STRICT_1_OF_2(create)
+    create _ [] = (Tip, [])
+    create s xs@(x' : xs')
+      | s == 1 = case x' of (kx, x) -> x `seq` (Bin 1 kx x Tip Tip, xs')
+      | otherwise = case create (s `shiftR` 1) xs of
+                      res@(_, []) -> res
+                      (l, (ky, y):ys) -> case create (s `shiftR` 1) ys of
+                        (r, zs) -> y `seq` (link ky y l r, zs)
diff --git a/Data/Sequence.hs b/Data/Sequence.hs
new file mode 100644
--- /dev/null
+++ b/Data/Sequence.hs
@@ -0,0 +1,1804 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE DeriveDataTypeable, StandaloneDeriving #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Sequence
+-- Copyright   :  (c) Ross Paterson 2005
+--                (c) Louis Wasserman 2009
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- General purpose finite sequences.
+-- Apart from being finite and having strict operations, sequences
+-- also differ from lists in supporting a wider variety of operations
+-- efficiently.
+--
+-- An amortized running time is given for each operation, with /n/ referring
+-- to the length of the sequence and /i/ being the integral index used by
+-- some operations.  These bounds hold even in a persistent (shared) setting.
+--
+-- The implementation uses 2-3 finger trees annotated with sizes,
+-- as described in section 4.2 of
+--
+--    * Ralf Hinze and Ross Paterson,
+--      \"Finger trees: a simple general-purpose data structure\",
+--      /Journal of Functional Programming/ 16:2 (2006) pp 197-217.
+--      <http://www.soi.city.ac.uk/~ross/papers/FingerTree.html>
+--
+-- /Note/: Many of these operations have the same names as similar
+-- operations on lists in the "Prelude".  The ambiguity may be resolved
+-- using either qualification or the @hiding@ clause.
+--
+-----------------------------------------------------------------------------
+
+module Data.Sequence (
+#if !defined(TESTING)
+    Seq,
+#else
+    Seq(..), Elem(..), FingerTree(..), Node(..), Digit(..),
+#endif
+    -- * Construction
+    empty,          -- :: Seq a
+    singleton,      -- :: a -> Seq a
+    (<|),           -- :: a -> Seq a -> Seq a
+    (|>),           -- :: Seq a -> a -> Seq a
+    (><),           -- :: Seq a -> Seq a -> Seq a
+    fromList,       -- :: [a] -> Seq a
+    -- ** Repetition
+    replicate,      -- :: Int -> a -> Seq a
+    replicateA,     -- :: Applicative f => Int -> f a -> f (Seq a)
+    replicateM,     -- :: Monad m => Int -> m a -> m (Seq a)
+    -- ** Iterative construction
+    iterateN,       -- :: Int -> (a -> a) -> a -> Seq a
+    unfoldr,        -- :: (b -> Maybe (a, b)) -> b -> Seq a
+    unfoldl,        -- :: (b -> Maybe (b, a)) -> b -> Seq a
+    -- * Deconstruction
+    -- | Additional functions for deconstructing sequences are available
+    -- via the 'Foldable' instance of 'Seq'.
+
+    -- ** Queries
+    null,           -- :: Seq a -> Bool
+    length,         -- :: Seq a -> Int
+    -- ** Views
+    ViewL(..),
+    viewl,          -- :: Seq a -> ViewL a
+    ViewR(..),
+    viewr,          -- :: Seq a -> ViewR a
+    -- * Scans
+    scanl,          -- :: (a -> b -> a) -> a -> Seq b -> Seq a
+    scanl1,         -- :: (a -> a -> a) -> Seq a -> Seq a
+    scanr,          -- :: (a -> b -> b) -> b -> Seq a -> Seq b
+    scanr1,         -- :: (a -> a -> a) -> Seq a -> Seq a
+    -- * Sublists
+    tails,          -- :: Seq a -> Seq (Seq a)
+    inits,          -- :: Seq a -> Seq (Seq a)
+    -- ** Sequential searches
+    takeWhileL,     -- :: (a -> Bool) -> Seq a -> Seq a
+    takeWhileR,     -- :: (a -> Bool) -> Seq a -> Seq a
+    dropWhileL,     -- :: (a -> Bool) -> Seq a -> Seq a
+    dropWhileR,     -- :: (a -> Bool) -> Seq a -> Seq a
+    spanl,          -- :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+    spanr,          -- :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+    breakl,         -- :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+    breakr,         -- :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+    partition,      -- :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+    filter,         -- :: (a -> Bool) -> Seq a -> Seq a
+    -- * Sorting
+    sort,           -- :: Ord a => Seq a -> Seq a
+    sortBy,         -- :: (a -> a -> Ordering) -> Seq a -> Seq a
+    unstableSort,   -- :: Ord a => Seq a -> Seq a
+    unstableSortBy, -- :: (a -> a -> Ordering) -> Seq a -> Seq a
+    -- * Indexing
+    index,          -- :: Seq a -> Int -> a
+    adjust,         -- :: (a -> a) -> Int -> Seq a -> Seq a
+    update,         -- :: Int -> a -> Seq a -> Seq a
+    take,           -- :: Int -> Seq a -> Seq a
+    drop,           -- :: Int -> Seq a -> Seq a
+    splitAt,        -- :: Int -> Seq a -> (Seq a, Seq a)
+    -- ** Indexing with predicates
+    -- | These functions perform sequential searches from the left
+    -- or right ends of the sequence, returning indices of matching
+    -- elements.
+    elemIndexL,     -- :: Eq a => a -> Seq a -> Maybe Int
+    elemIndicesL,   -- :: Eq a => a -> Seq a -> [Int]
+    elemIndexR,     -- :: Eq a => a -> Seq a -> Maybe Int
+    elemIndicesR,   -- :: Eq a => a -> Seq a -> [Int]
+    findIndexL,     -- :: (a -> Bool) -> Seq a -> Maybe Int
+    findIndicesL,   -- :: (a -> Bool) -> Seq a -> [Int]
+    findIndexR,     -- :: (a -> Bool) -> Seq a -> Maybe Int
+    findIndicesR,   -- :: (a -> Bool) -> Seq a -> [Int]
+    -- * Folds
+    -- | General folds are available via the 'Foldable' instance of 'Seq'.
+    foldlWithIndex, -- :: (b -> Int -> a -> b) -> b -> Seq a -> b
+    foldrWithIndex, -- :: (Int -> a -> b -> b) -> b -> Seq a -> b
+    -- * Transformations
+    mapWithIndex,   -- :: (Int -> a -> b) -> Seq a -> Seq b
+    reverse,        -- :: Seq a -> Seq a
+    -- ** Zips
+    zip,            -- :: Seq a -> Seq b -> Seq (a, b)
+    zipWith,        -- :: (a -> b -> c) -> Seq a -> Seq b -> Seq c
+    zip3,           -- :: Seq a -> Seq b -> Seq c -> Seq (a, b, c)
+    zipWith3,       -- :: (a -> b -> c -> d) -> Seq a -> Seq b -> Seq c -> Seq d
+    zip4,           -- :: Seq a -> Seq b -> Seq c -> Seq d -> Seq (a, b, c, d)
+    zipWith4,       -- :: (a -> b -> c -> d -> e) -> Seq a -> Seq b -> Seq c -> Seq d -> Seq e
+#if TESTING
+    Sized(..),
+    deep,
+    node2,
+    node3,
+#endif
+    ) where
+
+import Prelude hiding (
+    Functor(..),
+    null, length, take, drop, splitAt, foldl, foldl1, foldr, foldr1,
+    scanl, scanl1, scanr, scanr1, replicate, zip, zipWith, zip3, zipWith3,
+    takeWhile, dropWhile, iterate, reverse, filter, mapM, sum, all)
+import qualified Data.List
+import Control.Applicative (Applicative(..), (<$>), Alternative,
+                            WrappedMonad(..), liftA, liftA2, liftA3)
+import qualified Control.Applicative as Applicative (Alternative(..))
+import Control.DeepSeq (NFData(rnf))
+import Control.Monad (MonadPlus(..), ap)
+import Data.Monoid (Monoid(..))
+import Data.Functor (Functor(..))
+import Data.Foldable
+import Data.Traversable
+import Data.Typeable
+
+#ifdef __GLASGOW_HASKELL__
+import GHC.Exts (build)
+import Text.Read (Lexeme(Ident), lexP, parens, prec,
+    readPrec, readListPrec, readListPrecDefault)
+import Data.Data
+#endif
+
+infixr 5 `consTree`
+infixl 5 `snocTree`
+
+infixr 5 ><
+infixr 5 <|, :<
+infixl 5 |>, :>
+
+class Sized a where
+    size :: a -> Int
+
+-- | General-purpose finite sequences.
+newtype Seq a = Seq (FingerTree (Elem a))
+
+instance Functor Seq where
+    fmap f (Seq xs) = Seq (fmap (fmap f) xs)
+#ifdef __GLASGOW_HASKELL__
+    x <$ s = replicate (length s) x
+#endif
+
+instance Foldable Seq where
+    foldr f z (Seq xs) = foldr (flip (foldr f)) z xs
+    foldl f z (Seq xs) = foldl (foldl f) z xs
+
+    foldr1 f (Seq xs) = getElem (foldr1 f' xs)
+      where f' (Elem x) (Elem y) = Elem (f x y)
+
+    foldl1 f (Seq xs) = getElem (foldl1 f' xs)
+      where f' (Elem x) (Elem y) = Elem (f x y)
+
+instance Traversable Seq where
+    traverse f (Seq xs) = Seq <$> traverse (traverse f) xs
+
+instance NFData a => NFData (Seq a) where
+    rnf (Seq xs) = rnf xs
+
+instance Monad Seq where
+    return = singleton
+    xs >>= f = foldl' add empty xs
+      where add ys x = ys >< f x
+
+instance Applicative Seq where
+    pure = singleton
+    fs <*> xs = foldl' add empty fs
+      where add ys f = ys >< fmap f xs
+
+instance MonadPlus Seq where
+    mzero = empty
+    mplus = (><)
+
+instance Alternative Seq where
+    empty = empty
+    (<|>) = (><)
+
+instance Eq a => Eq (Seq a) where
+    xs == ys = length xs == length ys && toList xs == toList ys
+
+instance Ord a => Ord (Seq a) where
+    compare xs ys = compare (toList xs) (toList ys)
+
+#if TESTING
+instance Show a => Show (Seq a) where
+    showsPrec p (Seq x) = showsPrec p x
+#else
+instance Show a => Show (Seq a) where
+    showsPrec p xs = showParen (p > 10) $
+        showString "fromList " . shows (toList xs)
+#endif
+
+instance Read a => Read (Seq a) where
+#ifdef __GLASGOW_HASKELL__
+    readPrec = parens $ prec 10 $ do
+        Ident "fromList" <- lexP
+        xs <- readPrec
+        return (fromList xs)
+
+    readListPrec = readListPrecDefault
+#else
+    readsPrec p = readParen (p > 10) $ \ r -> do
+        ("fromList",s) <- lex r
+        (xs,t) <- reads s
+        return (fromList xs,t)
+#endif
+
+instance Monoid (Seq a) where
+    mempty = empty
+    mappend = (><)
+
+#include "Typeable.h"
+INSTANCE_TYPEABLE1(Seq,seqTc,"Seq")
+
+#if __GLASGOW_HASKELL__
+instance Data a => Data (Seq a) where
+    gfoldl f z s    = case viewl s of
+        EmptyL  -> z empty
+        x :< xs -> z (<|) `f` x `f` xs
+
+    gunfold k z c   = case constrIndex c of
+        1 -> z empty
+        2 -> k (k (z (<|)))
+        _ -> error "gunfold"
+
+    toConstr xs
+      | null xs     = emptyConstr
+      | otherwise   = consConstr
+
+    dataTypeOf _    = seqDataType
+
+    dataCast1 f     = gcast1 f
+
+emptyConstr, consConstr :: Constr
+emptyConstr = mkConstr seqDataType "empty" [] Prefix
+consConstr  = mkConstr seqDataType "<|" [] Infix
+
+seqDataType :: DataType
+seqDataType = mkDataType "Data.Sequence.Seq" [emptyConstr, consConstr]
+#endif
+
+-- Finger trees
+
+data FingerTree a
+    = Empty
+    | Single a
+    | Deep {-# UNPACK #-} !Int !(Digit a) (FingerTree (Node a)) !(Digit a)
+#if TESTING
+    deriving Show
+#endif
+
+instance Sized a => Sized (FingerTree a) where
+    {-# SPECIALIZE instance Sized (FingerTree (Elem a)) #-}
+    {-# SPECIALIZE instance Sized (FingerTree (Node a)) #-}
+    size Empty              = 0
+    size (Single x)         = size x
+    size (Deep v _ _ _)     = v
+
+instance Foldable FingerTree where
+    foldr _ z Empty = z
+    foldr f z (Single x) = x `f` z
+    foldr f z (Deep _ pr m sf) =
+        foldr f (foldr (flip (foldr f)) (foldr f z sf) m) pr
+
+    foldl _ z Empty = z
+    foldl f z (Single x) = z `f` x
+    foldl f z (Deep _ pr m sf) =
+        foldl f (foldl (foldl f) (foldl f z pr) m) sf
+
+    foldr1 _ Empty = error "foldr1: empty sequence"
+    foldr1 _ (Single x) = x
+    foldr1 f (Deep _ pr m sf) =
+        foldr f (foldr (flip (foldr f)) (foldr1 f sf) m) pr
+
+    foldl1 _ Empty = error "foldl1: empty sequence"
+    foldl1 _ (Single x) = x
+    foldl1 f (Deep _ pr m sf) =
+        foldl f (foldl (foldl f) (foldl1 f pr) m) sf
+
+instance Functor FingerTree where
+    fmap _ Empty = Empty
+    fmap f (Single x) = Single (f x)
+    fmap f (Deep v pr m sf) =
+        Deep v (fmap f pr) (fmap (fmap f) m) (fmap f sf)
+
+instance Traversable FingerTree where
+    traverse _ Empty = pure Empty
+    traverse f (Single x) = Single <$> f x
+    traverse f (Deep v pr m sf) =
+        Deep v <$> traverse f pr <*> traverse (traverse f) m <*>
+            traverse f sf
+
+instance NFData a => NFData (FingerTree a) where
+    rnf (Empty) = ()
+    rnf (Single x) = rnf x
+    rnf (Deep _ pr m sf) = rnf pr `seq` rnf m `seq` rnf sf
+
+{-# INLINE deep #-}
+deep            :: Sized a => Digit a -> FingerTree (Node a) -> Digit a -> FingerTree a
+deep pr m sf    =  Deep (size pr + size m + size sf) pr m sf
+
+{-# INLINE pullL #-}
+pullL :: Sized a => Int -> FingerTree (Node a) -> Digit a -> FingerTree a
+pullL s m sf = case viewLTree m of
+    Nothing2        -> digitToTree' s sf
+    Just2 pr m'     -> Deep s (nodeToDigit pr) m' sf
+
+{-# INLINE pullR #-}
+pullR :: Sized a => Int -> Digit a -> FingerTree (Node a) -> FingerTree a
+pullR s pr m = case viewRTree m of
+    Nothing2        -> digitToTree' s pr
+    Just2 m' sf     -> Deep s pr m' (nodeToDigit sf)
+
+{-# SPECIALIZE deepL :: Maybe (Digit (Elem a)) -> FingerTree (Node (Elem a)) -> Digit (Elem a) -> FingerTree (Elem a) #-}
+{-# SPECIALIZE deepL :: Maybe (Digit (Node a)) -> FingerTree (Node (Node a)) -> Digit (Node a) -> FingerTree (Node a) #-}
+deepL :: Sized a => Maybe (Digit a) -> FingerTree (Node a) -> Digit a -> FingerTree a
+deepL Nothing m sf      = pullL (size m + size sf) m sf
+deepL (Just pr) m sf    = deep pr m sf
+
+{-# SPECIALIZE deepR :: Digit (Elem a) -> FingerTree (Node (Elem a)) -> Maybe (Digit (Elem a)) -> FingerTree (Elem a) #-}
+{-# SPECIALIZE deepR :: Digit (Node a) -> FingerTree (Node (Node a)) -> Maybe (Digit (Node a)) -> FingerTree (Node a) #-}
+deepR :: Sized a => Digit a -> FingerTree (Node a) -> Maybe (Digit a) -> FingerTree a
+deepR pr m Nothing      = pullR (size m + size pr) pr m
+deepR pr m (Just sf)    = deep pr m sf
+
+-- Digits
+
+data Digit a
+    = One a
+    | Two a a
+    | Three a a a
+    | Four a a a a
+#if TESTING
+    deriving Show
+#endif
+
+instance Foldable Digit where
+    foldr f z (One a) = a `f` z
+    foldr f z (Two a b) = a `f` (b `f` z)
+    foldr f z (Three a b c) = a `f` (b `f` (c `f` z))
+    foldr f z (Four a b c d) = a `f` (b `f` (c `f` (d `f` z)))
+
+    foldl f z (One a) = z `f` a
+    foldl f z (Two a b) = (z `f` a) `f` b
+    foldl f z (Three a b c) = ((z `f` a) `f` b) `f` c
+    foldl f z (Four a b c d) = (((z `f` a) `f` b) `f` c) `f` d
+
+    foldr1 _ (One a) = a
+    foldr1 f (Two a b) = a `f` b
+    foldr1 f (Three a b c) = a `f` (b `f` c)
+    foldr1 f (Four a b c d) = a `f` (b `f` (c `f` d))
+
+    foldl1 _ (One a) = a
+    foldl1 f (Two a b) = a `f` b
+    foldl1 f (Three a b c) = (a `f` b) `f` c
+    foldl1 f (Four a b c d) = ((a `f` b) `f` c) `f` d
+
+instance Functor Digit where
+    {-# INLINE fmap #-}
+    fmap f (One a) = One (f a)
+    fmap f (Two a b) = Two (f a) (f b)
+    fmap f (Three a b c) = Three (f a) (f b) (f c)
+    fmap f (Four a b c d) = Four (f a) (f b) (f c) (f d)
+
+instance Traversable Digit where
+    {-# INLINE traverse #-}
+    traverse f (One a) = One <$> f a
+    traverse f (Two a b) = Two <$> f a <*> f b
+    traverse f (Three a b c) = Three <$> f a <*> f b <*> f c
+    traverse f (Four a b c d) = Four <$> f a <*> f b <*> f c <*> f d
+
+instance NFData a => NFData (Digit a) where
+    rnf (One a) = rnf a
+    rnf (Two a b) = rnf a `seq` rnf b
+    rnf (Three a b c) = rnf a `seq` rnf b `seq` rnf c
+    rnf (Four a b c d) = rnf a `seq` rnf b `seq` rnf c `seq` rnf d
+
+instance Sized a => Sized (Digit a) where
+    {-# INLINE size #-}
+    size = foldl1 (+) . fmap size
+
+{-# SPECIALIZE digitToTree :: Digit (Elem a) -> FingerTree (Elem a) #-}
+{-# SPECIALIZE digitToTree :: Digit (Node a) -> FingerTree (Node a) #-}
+digitToTree     :: Sized a => Digit a -> FingerTree a
+digitToTree (One a) = Single a
+digitToTree (Two a b) = deep (One a) Empty (One b)
+digitToTree (Three a b c) = deep (Two a b) Empty (One c)
+digitToTree (Four a b c d) = deep (Two a b) Empty (Two c d)
+
+-- | Given the size of a digit and the digit itself, efficiently converts
+-- it to a FingerTree.
+digitToTree' :: Int -> Digit a -> FingerTree a
+digitToTree' n (Four a b c d) = Deep n (Two a b) Empty (Two c d)
+digitToTree' n (Three a b c) = Deep n (Two a b) Empty (One c)
+digitToTree' n (Two a b) = Deep n (One a) Empty (One b)
+digitToTree' n (One a) = n `seq` Single a
+
+-- Nodes
+
+data Node a
+    = Node2 {-# UNPACK #-} !Int a a
+    | Node3 {-# UNPACK #-} !Int a a a
+#if TESTING
+    deriving Show
+#endif
+
+instance Foldable Node where
+    foldr f z (Node2 _ a b) = a `f` (b `f` z)
+    foldr f z (Node3 _ a b c) = a `f` (b `f` (c `f` z))
+
+    foldl f z (Node2 _ a b) = (z `f` a) `f` b
+    foldl f z (Node3 _ a b c) = ((z `f` a) `f` b) `f` c
+
+instance Functor Node where
+    {-# INLINE fmap #-}
+    fmap f (Node2 v a b) = Node2 v (f a) (f b)
+    fmap f (Node3 v a b c) = Node3 v (f a) (f b) (f c)
+
+instance Traversable Node where
+    {-# INLINE traverse #-}
+    traverse f (Node2 v a b) = Node2 v <$> f a <*> f b
+    traverse f (Node3 v a b c) = Node3 v <$> f a <*> f b <*> f c
+
+instance NFData a => NFData (Node a) where
+    rnf (Node2 _ a b) = rnf a `seq` rnf b
+    rnf (Node3 _ a b c) = rnf a `seq` rnf b `seq` rnf c
+
+instance Sized (Node a) where
+    size (Node2 v _ _)      = v
+    size (Node3 v _ _ _)    = v
+
+{-# INLINE node2 #-}
+node2           :: Sized a => a -> a -> Node a
+node2 a b       =  Node2 (size a + size b) a b
+
+{-# INLINE node3 #-}
+node3           :: Sized a => a -> a -> a -> Node a
+node3 a b c     =  Node3 (size a + size b + size c) a b c
+
+nodeToDigit :: Node a -> Digit a
+nodeToDigit (Node2 _ a b) = Two a b
+nodeToDigit (Node3 _ a b c) = Three a b c
+
+-- Elements
+
+newtype Elem a  =  Elem { getElem :: a }
+#if TESTING
+    deriving Show
+#endif
+
+instance Sized (Elem a) where
+    size _ = 1
+
+instance Functor Elem where
+    fmap f (Elem x) = Elem (f x)
+
+instance Foldable Elem where
+    foldr f z (Elem x) = f x z
+    foldl f z (Elem x) = f z x
+
+instance Traversable Elem where
+    traverse f (Elem x) = Elem <$> f x
+
+instance NFData a => NFData (Elem a) where
+    rnf (Elem x) = rnf x
+
+-------------------------------------------------------
+-- Applicative construction
+-------------------------------------------------------
+
+newtype Id a = Id {runId :: a}
+
+instance Functor Id where
+    fmap f (Id x) = Id (f x)
+
+instance Monad Id where
+    return = Id
+    m >>= k = k (runId m)
+
+instance Applicative Id where
+    pure = return
+    (<*>) = ap
+
+-- | This is essentially a clone of Control.Monad.State.Strict.
+newtype State s a = State {runState :: s -> (s, a)}
+
+instance Functor (State s) where
+    fmap = liftA
+
+instance Monad (State s) where
+    {-# INLINE return #-}
+    {-# INLINE (>>=) #-}
+    return x = State $ \ s -> (s, x)
+    m >>= k = State $ \ s -> case runState m s of
+        (s', x) -> runState (k x) s'
+
+instance Applicative (State s) where
+    pure = return
+    (<*>) = ap
+
+execState :: State s a -> s -> a
+execState m x = snd (runState m x)
+
+-- | A helper method: a strict version of mapAccumL.
+mapAccumL' :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c)
+mapAccumL' f s t = runState (traverse (State . flip f) t) s
+
+-- | 'applicativeTree' takes an Applicative-wrapped construction of a
+-- piece of a FingerTree, assumed to always have the same size (which
+-- is put in the second argument), and replicates it as many times as
+-- specified.  This is a generalization of 'replicateA', which itself
+-- is a generalization of many Data.Sequence methods.
+{-# SPECIALIZE applicativeTree :: Int -> Int -> State s a -> State s (FingerTree a) #-}
+{-# SPECIALIZE applicativeTree :: Int -> Int -> Id a -> Id (FingerTree a) #-}
+-- Special note: the Id specialization automatically does node sharing,
+-- reducing memory usage of the resulting tree to /O(log n)/.
+applicativeTree :: Applicative f => Int -> Int -> f a -> f (FingerTree a)
+applicativeTree n mSize m = mSize `seq` case n of
+    0 -> pure Empty
+    1 -> liftA Single m
+    2 -> deepA one emptyTree one
+    3 -> deepA two emptyTree one
+    4 -> deepA two emptyTree two
+    5 -> deepA three emptyTree two
+    6 -> deepA three emptyTree three
+    7 -> deepA four emptyTree three
+    8 -> deepA four emptyTree four
+    _ -> let (q, r) = n `quotRem` 3 in q `seq` case r of
+        0 -> deepA three (applicativeTree (q - 2) mSize' n3) three
+        1 -> deepA four (applicativeTree (q - 2) mSize' n3) three
+        _ -> deepA four (applicativeTree (q - 2) mSize' n3) four
+  where
+    one = liftA One m
+    two = liftA2 Two m m
+    three = liftA3 Three m m m
+    four = liftA3 Four m m m <*> m
+    deepA = liftA3 (Deep (n * mSize))
+    mSize' = 3 * mSize
+    n3 = liftA3 (Node3 mSize') m m m
+    emptyTree = pure Empty
+
+------------------------------------------------------------------------
+-- Construction
+------------------------------------------------------------------------
+
+-- | /O(1)/. The empty sequence.
+empty           :: Seq a
+empty           =  Seq Empty
+
+-- | /O(1)/. A singleton sequence.
+singleton       :: a -> Seq a
+singleton x     =  Seq (Single (Elem x))
+
+-- | /O(log n)/. @replicate n x@ is a sequence consisting of @n@ copies of @x@.
+replicate       :: Int -> a -> Seq a
+replicate n x
+  | n >= 0      = runId (replicateA n (Id x))
+  | otherwise   = error "replicate takes a nonnegative integer argument"
+
+-- | 'replicateA' is an 'Applicative' version of 'replicate', and makes
+-- /O(log n)/ calls to '<*>' and 'pure'.
+--
+-- > replicateA n x = sequenceA (replicate n x)
+replicateA :: Applicative f => Int -> f a -> f (Seq a)
+replicateA n x
+  | n >= 0      = Seq <$> applicativeTree n 1 (Elem <$> x)
+  | otherwise   = error "replicateA takes a nonnegative integer argument"
+
+-- | 'replicateM' is a sequence counterpart of 'Control.Monad.replicateM'.
+--
+-- > replicateM n x = sequence (replicate n x)
+replicateM :: Monad m => Int -> m a -> m (Seq a)
+replicateM n x
+  | n >= 0      = unwrapMonad (replicateA n (WrapMonad x))
+  | otherwise   = error "replicateM takes a nonnegative integer argument"
+
+-- | /O(1)/. Add an element to the left end of a sequence.
+-- Mnemonic: a triangle with the single element at the pointy end.
+(<|)            :: a -> Seq a -> Seq a
+x <| Seq xs     =  Seq (Elem x `consTree` xs)
+
+{-# SPECIALIZE consTree :: Elem a -> FingerTree (Elem a) -> FingerTree (Elem a) #-}
+{-# SPECIALIZE consTree :: Node a -> FingerTree (Node a) -> FingerTree (Node a) #-}
+consTree        :: Sized a => a -> FingerTree a -> FingerTree a
+consTree a Empty        = Single a
+consTree a (Single b)   = deep (One a) Empty (One b)
+consTree a (Deep s (Four b c d e) m sf) = m `seq`
+    Deep (size a + s) (Two a b) (node3 c d e `consTree` m) sf
+consTree a (Deep s (Three b c d) m sf) =
+    Deep (size a + s) (Four a b c d) m sf
+consTree a (Deep s (Two b c) m sf) =
+    Deep (size a + s) (Three a b c) m sf
+consTree a (Deep s (One b) m sf) =
+    Deep (size a + s) (Two a b) m sf
+
+-- | /O(1)/. Add an element to the right end of a sequence.
+-- Mnemonic: a triangle with the single element at the pointy end.
+(|>)            :: Seq a -> a -> Seq a
+Seq xs |> x     =  Seq (xs `snocTree` Elem x)
+
+{-# SPECIALIZE snocTree :: FingerTree (Elem a) -> Elem a -> FingerTree (Elem a) #-}
+{-# SPECIALIZE snocTree :: FingerTree (Node a) -> Node a -> FingerTree (Node a) #-}
+snocTree        :: Sized a => FingerTree a -> a -> FingerTree a
+snocTree Empty a        =  Single a
+snocTree (Single a) b   =  deep (One a) Empty (One b)
+snocTree (Deep s pr m (Four a b c d)) e = m `seq`
+    Deep (s + size e) pr (m `snocTree` node3 a b c) (Two d e)
+snocTree (Deep s pr m (Three a b c)) d =
+    Deep (s + size d) pr m (Four a b c d)
+snocTree (Deep s pr m (Two a b)) c =
+    Deep (s + size c) pr m (Three a b c)
+snocTree (Deep s pr m (One a)) b =
+    Deep (s + size b) pr m (Two a b)
+
+-- | /O(log(min(n1,n2)))/. Concatenate two sequences.
+(><)            :: Seq a -> Seq a -> Seq a
+Seq xs >< Seq ys = Seq (appendTree0 xs ys)
+
+-- The appendTree/addDigits gunk below is machine generated
+
+appendTree0 :: FingerTree (Elem a) -> FingerTree (Elem a) -> FingerTree (Elem a)
+appendTree0 Empty xs =
+    xs
+appendTree0 xs Empty =
+    xs
+appendTree0 (Single x) xs =
+    x `consTree` xs
+appendTree0 xs (Single x) =
+    xs `snocTree` x
+appendTree0 (Deep s1 pr1 m1 sf1) (Deep s2 pr2 m2 sf2) =
+    Deep (s1 + s2) pr1 (addDigits0 m1 sf1 pr2 m2) sf2
+
+addDigits0 :: FingerTree (Node (Elem a)) -> Digit (Elem a) -> Digit (Elem a) -> FingerTree (Node (Elem a)) -> FingerTree (Node (Elem a))
+addDigits0 m1 (One a) (One b) m2 =
+    appendTree1 m1 (node2 a b) m2
+addDigits0 m1 (One a) (Two b c) m2 =
+    appendTree1 m1 (node3 a b c) m2
+addDigits0 m1 (One a) (Three b c d) m2 =
+    appendTree2 m1 (node2 a b) (node2 c d) m2
+addDigits0 m1 (One a) (Four b c d e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits0 m1 (Two a b) (One c) m2 =
+    appendTree1 m1 (node3 a b c) m2
+addDigits0 m1 (Two a b) (Two c d) m2 =
+    appendTree2 m1 (node2 a b) (node2 c d) m2
+addDigits0 m1 (Two a b) (Three c d e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits0 m1 (Two a b) (Four c d e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits0 m1 (Three a b c) (One d) m2 =
+    appendTree2 m1 (node2 a b) (node2 c d) m2
+addDigits0 m1 (Three a b c) (Two d e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits0 m1 (Three a b c) (Three d e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits0 m1 (Three a b c) (Four d e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits0 m1 (Four a b c d) (One e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits0 m1 (Four a b c d) (Two e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits0 m1 (Four a b c d) (Three e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits0 m1 (Four a b c d) (Four e f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+
+appendTree1 :: FingerTree (Node a) -> Node a -> FingerTree (Node a) -> FingerTree (Node a)
+appendTree1 Empty a xs =
+    a `consTree` xs
+appendTree1 xs a Empty =
+    xs `snocTree` a
+appendTree1 (Single x) a xs =
+    x `consTree` a `consTree` xs
+appendTree1 xs a (Single x) =
+    xs `snocTree` a `snocTree` x
+appendTree1 (Deep s1 pr1 m1 sf1) a (Deep s2 pr2 m2 sf2) =
+    Deep (s1 + size a + s2) pr1 (addDigits1 m1 sf1 a pr2 m2) sf2
+
+addDigits1 :: FingerTree (Node (Node a)) -> Digit (Node a) -> Node a -> Digit (Node a) -> FingerTree (Node (Node a)) -> FingerTree (Node (Node a))
+addDigits1 m1 (One a) b (One c) m2 =
+    appendTree1 m1 (node3 a b c) m2
+addDigits1 m1 (One a) b (Two c d) m2 =
+    appendTree2 m1 (node2 a b) (node2 c d) m2
+addDigits1 m1 (One a) b (Three c d e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits1 m1 (One a) b (Four c d e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits1 m1 (Two a b) c (One d) m2 =
+    appendTree2 m1 (node2 a b) (node2 c d) m2
+addDigits1 m1 (Two a b) c (Two d e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits1 m1 (Two a b) c (Three d e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits1 m1 (Two a b) c (Four d e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits1 m1 (Three a b c) d (One e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits1 m1 (Three a b c) d (Two e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits1 m1 (Three a b c) d (Three e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits1 m1 (Three a b c) d (Four e f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits1 m1 (Four a b c d) e (One f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits1 m1 (Four a b c d) e (Two f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits1 m1 (Four a b c d) e (Three f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits1 m1 (Four a b c d) e (Four f g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+
+appendTree2 :: FingerTree (Node a) -> Node a -> Node a -> FingerTree (Node a) -> FingerTree (Node a)
+appendTree2 Empty a b xs =
+    a `consTree` b `consTree` xs
+appendTree2 xs a b Empty =
+    xs `snocTree` a `snocTree` b
+appendTree2 (Single x) a b xs =
+    x `consTree` a `consTree` b `consTree` xs
+appendTree2 xs a b (Single x) =
+    xs `snocTree` a `snocTree` b `snocTree` x
+appendTree2 (Deep s1 pr1 m1 sf1) a b (Deep s2 pr2 m2 sf2) =
+    Deep (s1 + size a + size b + s2) pr1 (addDigits2 m1 sf1 a b pr2 m2) sf2
+
+addDigits2 :: FingerTree (Node (Node a)) -> Digit (Node a) -> Node a -> Node a -> Digit (Node a) -> FingerTree (Node (Node a)) -> FingerTree (Node (Node a))
+addDigits2 m1 (One a) b c (One d) m2 =
+    appendTree2 m1 (node2 a b) (node2 c d) m2
+addDigits2 m1 (One a) b c (Two d e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits2 m1 (One a) b c (Three d e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits2 m1 (One a) b c (Four d e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits2 m1 (Two a b) c d (One e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits2 m1 (Two a b) c d (Two e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits2 m1 (Two a b) c d (Three e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits2 m1 (Two a b) c d (Four e f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits2 m1 (Three a b c) d e (One f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits2 m1 (Three a b c) d e (Two f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits2 m1 (Three a b c) d e (Three f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits2 m1 (Three a b c) d e (Four f g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits2 m1 (Four a b c d) e f (One g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits2 m1 (Four a b c d) e f (Two g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits2 m1 (Four a b c d) e f (Three g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits2 m1 (Four a b c d) e f (Four g h i j) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node2 g h) (node2 i j) m2
+
+appendTree3 :: FingerTree (Node a) -> Node a -> Node a -> Node a -> FingerTree (Node a) -> FingerTree (Node a)
+appendTree3 Empty a b c xs =
+    a `consTree` b `consTree` c `consTree` xs
+appendTree3 xs a b c Empty =
+    xs `snocTree` a `snocTree` b `snocTree` c
+appendTree3 (Single x) a b c xs =
+    x `consTree` a `consTree` b `consTree` c `consTree` xs
+appendTree3 xs a b c (Single x) =
+    xs `snocTree` a `snocTree` b `snocTree` c `snocTree` x
+appendTree3 (Deep s1 pr1 m1 sf1) a b c (Deep s2 pr2 m2 sf2) =
+    Deep (s1 + size a + size b + size c + s2) pr1 (addDigits3 m1 sf1 a b c pr2 m2) sf2
+
+addDigits3 :: FingerTree (Node (Node a)) -> Digit (Node a) -> Node a -> Node a -> Node a -> Digit (Node a) -> FingerTree (Node (Node a)) -> FingerTree (Node (Node a))
+addDigits3 m1 (One a) b c d (One e) m2 =
+    appendTree2 m1 (node3 a b c) (node2 d e) m2
+addDigits3 m1 (One a) b c d (Two e f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits3 m1 (One a) b c d (Three e f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits3 m1 (One a) b c d (Four e f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits3 m1 (Two a b) c d e (One f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits3 m1 (Two a b) c d e (Two f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits3 m1 (Two a b) c d e (Three f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits3 m1 (Two a b) c d e (Four f g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits3 m1 (Three a b c) d e f (One g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits3 m1 (Three a b c) d e f (Two g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits3 m1 (Three a b c) d e f (Three g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits3 m1 (Three a b c) d e f (Four g h i j) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node2 g h) (node2 i j) m2
+addDigits3 m1 (Four a b c d) e f g (One h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits3 m1 (Four a b c d) e f g (Two h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits3 m1 (Four a b c d) e f g (Three h i j) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node2 g h) (node2 i j) m2
+addDigits3 m1 (Four a b c d) e f g (Four h i j k) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node3 g h i) (node2 j k) m2
+
+appendTree4 :: FingerTree (Node a) -> Node a -> Node a -> Node a -> Node a -> FingerTree (Node a) -> FingerTree (Node a)
+appendTree4 Empty a b c d xs =
+    a `consTree` b `consTree` c `consTree` d `consTree` xs
+appendTree4 xs a b c d Empty =
+    xs `snocTree` a `snocTree` b `snocTree` c `snocTree` d
+appendTree4 (Single x) a b c d xs =
+    x `consTree` a `consTree` b `consTree` c `consTree` d `consTree` xs
+appendTree4 xs a b c d (Single x) =
+    xs `snocTree` a `snocTree` b `snocTree` c `snocTree` d `snocTree` x
+appendTree4 (Deep s1 pr1 m1 sf1) a b c d (Deep s2 pr2 m2 sf2) =
+    Deep (s1 + size a + size b + size c + size d + s2) pr1 (addDigits4 m1 sf1 a b c d pr2 m2) sf2
+
+addDigits4 :: FingerTree (Node (Node a)) -> Digit (Node a) -> Node a -> Node a -> Node a -> Node a -> Digit (Node a) -> FingerTree (Node (Node a)) -> FingerTree (Node (Node a))
+addDigits4 m1 (One a) b c d e (One f) m2 =
+    appendTree2 m1 (node3 a b c) (node3 d e f) m2
+addDigits4 m1 (One a) b c d e (Two f g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits4 m1 (One a) b c d e (Three f g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits4 m1 (One a) b c d e (Four f g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits4 m1 (Two a b) c d e f (One g) m2 =
+    appendTree3 m1 (node3 a b c) (node2 d e) (node2 f g) m2
+addDigits4 m1 (Two a b) c d e f (Two g h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits4 m1 (Two a b) c d e f (Three g h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits4 m1 (Two a b) c d e f (Four g h i j) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node2 g h) (node2 i j) m2
+addDigits4 m1 (Three a b c) d e f g (One h) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node2 g h) m2
+addDigits4 m1 (Three a b c) d e f g (Two h i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits4 m1 (Three a b c) d e f g (Three h i j) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node2 g h) (node2 i j) m2
+addDigits4 m1 (Three a b c) d e f g (Four h i j k) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node3 g h i) (node2 j k) m2
+addDigits4 m1 (Four a b c d) e f g h (One i) m2 =
+    appendTree3 m1 (node3 a b c) (node3 d e f) (node3 g h i) m2
+addDigits4 m1 (Four a b c d) e f g h (Two i j) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node2 g h) (node2 i j) m2
+addDigits4 m1 (Four a b c d) e f g h (Three i j k) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node3 g h i) (node2 j k) m2
+addDigits4 m1 (Four a b c d) e f g h (Four i j k l) m2 =
+    appendTree4 m1 (node3 a b c) (node3 d e f) (node3 g h i) (node3 j k l) m2
+
+-- | Builds a sequence from a seed value.  Takes time linear in the
+-- number of generated elements.  /WARNING:/ If the number of generated
+-- elements is infinite, this method will not terminate.
+unfoldr :: (b -> Maybe (a, b)) -> b -> Seq a
+unfoldr f = unfoldr' empty
+  -- uses tail recursion rather than, for instance, the List implementation.
+  where unfoldr' as b = maybe as (\ (a, b') -> unfoldr' (as |> a) b') (f b)
+
+-- | @'unfoldl' f x@ is equivalent to @'reverse' ('unfoldr' ('fmap' swap . f) x)@.
+unfoldl :: (b -> Maybe (b, a)) -> b -> Seq a
+unfoldl f = unfoldl' empty
+  where unfoldl' as b = maybe as (\ (b', a) -> unfoldl' (a <| as) b') (f b)
+
+-- | /O(n)/.  Constructs a sequence by repeated application of a function
+-- to a seed value.
+--
+-- > iterateN n f x = fromList (Prelude.take n (Prelude.iterate f x))
+iterateN :: Int -> (a -> a) -> a -> Seq a
+iterateN n f x
+  | n >= 0      = replicateA n (State (\ y -> (f y, y))) `execState` x
+  | otherwise   = error "iterateN takes a nonnegative integer argument"
+
+------------------------------------------------------------------------
+-- Deconstruction
+------------------------------------------------------------------------
+
+-- | /O(1)/. Is this the empty sequence?
+null            :: Seq a -> Bool
+null (Seq Empty) = True
+null _          =  False
+
+-- | /O(1)/. The number of elements in the sequence.
+length          :: Seq a -> Int
+length (Seq xs) =  size xs
+
+-- Views
+
+data Maybe2 a b = Nothing2 | Just2 a b
+
+-- | View of the left end of a sequence.
+data ViewL a
+    = EmptyL        -- ^ empty sequence
+    | a :< Seq a    -- ^ leftmost element and the rest of the sequence
+#if __GLASGOW_HASKELL__
+    deriving (Eq, Ord, Show, Read, Data)
+#else
+    deriving (Eq, Ord, Show, Read)
+#endif
+
+INSTANCE_TYPEABLE1(ViewL,viewLTc,"ViewL")
+
+instance Functor ViewL where
+    {-# INLINE fmap #-}
+    fmap _ EmptyL       = EmptyL
+    fmap f (x :< xs)    = f x :< fmap f xs
+
+instance Foldable ViewL where
+    foldr _ z EmptyL = z
+    foldr f z (x :< xs) = f x (foldr f z xs)
+
+    foldl _ z EmptyL = z
+    foldl f z (x :< xs) = foldl f (f z x) xs
+
+    foldl1 _ EmptyL = error "foldl1: empty view"
+    foldl1 f (x :< xs) = foldl f x xs
+
+instance Traversable ViewL where
+    traverse _ EmptyL       = pure EmptyL
+    traverse f (x :< xs)    = (:<) <$> f x <*> traverse f xs
+
+-- | /O(1)/. Analyse the left end of a sequence.
+viewl           ::  Seq a -> ViewL a
+viewl (Seq xs)  =  case viewLTree xs of
+    Nothing2 -> EmptyL
+    Just2 (Elem x) xs' -> x :< Seq xs'
+
+{-# SPECIALIZE viewLTree :: FingerTree (Elem a) -> Maybe2 (Elem a) (FingerTree (Elem a)) #-}
+{-# SPECIALIZE viewLTree :: FingerTree (Node a) -> Maybe2 (Node a) (FingerTree (Node a)) #-}
+viewLTree       :: Sized a => FingerTree a -> Maybe2 a (FingerTree a)
+viewLTree Empty                 = Nothing2
+viewLTree (Single a)            = Just2 a Empty
+viewLTree (Deep s (One a) m sf) = Just2 a (pullL (s - size a) m sf)
+viewLTree (Deep s (Two a b) m sf) =
+    Just2 a (Deep (s - size a) (One b) m sf)
+viewLTree (Deep s (Three a b c) m sf) =
+    Just2 a (Deep (s - size a) (Two b c) m sf)
+viewLTree (Deep s (Four a b c d) m sf) =
+    Just2 a (Deep (s - size a) (Three b c d) m sf)
+
+-- | View of the right end of a sequence.
+data ViewR a
+    = EmptyR        -- ^ empty sequence
+    | Seq a :> a    -- ^ the sequence minus the rightmost element,
+            -- and the rightmost element
+#if __GLASGOW_HASKELL__
+    deriving (Eq, Ord, Show, Read, Data)
+#else
+    deriving (Eq, Ord, Show, Read)
+#endif
+
+INSTANCE_TYPEABLE1(ViewR,viewRTc,"ViewR")
+
+instance Functor ViewR where
+    {-# INLINE fmap #-}
+    fmap _ EmptyR       = EmptyR
+    fmap f (xs :> x)    = fmap f xs :> f x
+
+instance Foldable ViewR where
+    foldr _ z EmptyR = z
+    foldr f z (xs :> x) = foldr f (f x z) xs
+
+    foldl _ z EmptyR = z
+    foldl f z (xs :> x) = foldl f z xs `f` x
+
+    foldr1 _ EmptyR = error "foldr1: empty view"
+    foldr1 f (xs :> x) = foldr f x xs
+
+instance Traversable ViewR where
+    traverse _ EmptyR       = pure EmptyR
+    traverse f (xs :> x)    = (:>) <$> traverse f xs <*> f x
+
+-- | /O(1)/. Analyse the right end of a sequence.
+viewr           ::  Seq a -> ViewR a
+viewr (Seq xs)  =  case viewRTree xs of
+    Nothing2 -> EmptyR
+    Just2 xs' (Elem x) -> Seq xs' :> x
+
+{-# SPECIALIZE viewRTree :: FingerTree (Elem a) -> Maybe2 (FingerTree (Elem a)) (Elem a) #-}
+{-# SPECIALIZE viewRTree :: FingerTree (Node a) -> Maybe2 (FingerTree (Node a)) (Node a) #-}
+viewRTree       :: Sized a => FingerTree a -> Maybe2 (FingerTree a) a
+viewRTree Empty                 = Nothing2
+viewRTree (Single z)            = Just2 Empty z
+viewRTree (Deep s pr m (One z)) = Just2 (pullR (s - size z) pr m) z
+viewRTree (Deep s pr m (Two y z)) =
+    Just2 (Deep (s - size z) pr m (One y)) z
+viewRTree (Deep s pr m (Three x y z)) =
+    Just2 (Deep (s - size z) pr m (Two x y)) z
+viewRTree (Deep s pr m (Four w x y z)) =
+    Just2 (Deep (s - size z) pr m (Three w x y)) z
+
+------------------------------------------------------------------------
+-- Scans
+--
+-- These are not particularly complex applications of the Traversable
+-- functor, though making the correspondence with Data.List exact
+-- requires the use of (<|) and (|>).
+--
+-- Note that save for the single (<|) or (|>), we maintain the original
+-- structure of the Seq, not having to do any restructuring of our own.
+--
+-- wasserman.louis@gmail.com, 5/23/09
+------------------------------------------------------------------------
+
+-- | 'scanl' is similar to 'foldl', but returns a sequence of reduced
+-- values from the left:
+--
+-- > scanl f z (fromList [x1, x2, ...]) = fromList [z, z `f` x1, (z `f` x1) `f` x2, ...]
+scanl :: (a -> b -> a) -> a -> Seq b -> Seq a
+scanl f z0 xs = z0 <| snd (mapAccumL (\ x z -> let x' = f x z in (x', x')) z0 xs)
+
+-- | 'scanl1' is a variant of 'scanl' that has no starting value argument:
+--
+-- > scanl1 f (fromList [x1, x2, ...]) = fromList [x1, x1 `f` x2, ...]
+scanl1 :: (a -> a -> a) -> Seq a -> Seq a
+scanl1 f xs = case viewl xs of
+    EmptyL          -> error "scanl1 takes a nonempty sequence as an argument"
+    x :< xs'        -> scanl f x xs'
+
+-- | 'scanr' is the right-to-left dual of 'scanl'.
+scanr :: (a -> b -> b) -> b -> Seq a -> Seq b
+scanr f z0 xs = snd (mapAccumR (\ z x -> let z' = f x z in (z', z')) z0 xs) |> z0
+
+-- | 'scanr1' is a variant of 'scanr' that has no starting value argument.
+scanr1 :: (a -> a -> a) -> Seq a -> Seq a
+scanr1 f xs = case viewr xs of
+    EmptyR          -> error "scanr1 takes a nonempty sequence as an argument"
+    xs' :> x        -> scanr f x xs'
+
+-- Indexing
+
+-- | /O(log(min(i,n-i)))/. The element at the specified position,
+-- counting from 0.  The argument should thus be a non-negative
+-- integer less than the size of the sequence.
+-- If the position is out of range, 'index' fails with an error.
+index           :: Seq a -> Int -> a
+index (Seq xs) i
+  | 0 <= i && i < size xs = case lookupTree i xs of
+                Place _ (Elem x) -> x
+  | otherwise   = error "index out of bounds"
+
+data Place a = Place {-# UNPACK #-} !Int a
+#if TESTING
+    deriving Show
+#endif
+
+{-# SPECIALIZE lookupTree :: Int -> FingerTree (Elem a) -> Place (Elem a) #-}
+{-# SPECIALIZE lookupTree :: Int -> FingerTree (Node a) -> Place (Node a) #-}
+lookupTree :: Sized a => Int -> FingerTree a -> Place a
+lookupTree _ Empty = error "lookupTree of empty tree"
+lookupTree i (Single x) = Place i x
+lookupTree i (Deep _ pr m sf)
+  | i < spr     =  lookupDigit i pr
+  | i < spm     =  case lookupTree (i - spr) m of
+                   Place i' xs -> lookupNode i' xs
+  | otherwise   =  lookupDigit (i - spm) sf
+  where
+    spr     = size pr
+    spm     = spr + size m
+
+{-# SPECIALIZE lookupNode :: Int -> Node (Elem a) -> Place (Elem a) #-}
+{-# SPECIALIZE lookupNode :: Int -> Node (Node a) -> Place (Node a) #-}
+lookupNode :: Sized a => Int -> Node a -> Place a
+lookupNode i (Node2 _ a b)
+  | i < sa      = Place i a
+  | otherwise   = Place (i - sa) b
+  where
+    sa      = size a
+lookupNode i (Node3 _ a b c)
+  | i < sa      = Place i a
+  | i < sab     = Place (i - sa) b
+  | otherwise   = Place (i - sab) c
+  where
+    sa      = size a
+    sab     = sa + size b
+
+{-# SPECIALIZE lookupDigit :: Int -> Digit (Elem a) -> Place (Elem a) #-}
+{-# SPECIALIZE lookupDigit :: Int -> Digit (Node a) -> Place (Node a) #-}
+lookupDigit :: Sized a => Int -> Digit a -> Place a
+lookupDigit i (One a) = Place i a
+lookupDigit i (Two a b)
+  | i < sa      = Place i a
+  | otherwise   = Place (i - sa) b
+  where
+    sa      = size a
+lookupDigit i (Three a b c)
+  | i < sa      = Place i a
+  | i < sab     = Place (i - sa) b
+  | otherwise   = Place (i - sab) c
+  where
+    sa      = size a
+    sab     = sa + size b
+lookupDigit i (Four a b c d)
+  | i < sa      = Place i a
+  | i < sab     = Place (i - sa) b
+  | i < sabc    = Place (i - sab) c
+  | otherwise   = Place (i - sabc) d
+  where
+    sa      = size a
+    sab     = sa + size b
+    sabc    = sab + size c
+
+-- | /O(log(min(i,n-i)))/. Replace the element at the specified position.
+-- If the position is out of range, the original sequence is returned.
+update          :: Int -> a -> Seq a -> Seq a
+update i x      = adjust (const x) i
+
+-- | /O(log(min(i,n-i)))/. Update the element at the specified position.
+-- If the position is out of range, the original sequence is returned.
+adjust          :: (a -> a) -> Int -> Seq a -> Seq a
+adjust f i (Seq xs)
+  | 0 <= i && i < size xs = Seq (adjustTree (const (fmap f)) i xs)
+  | otherwise   = Seq xs
+
+{-# SPECIALIZE adjustTree :: (Int -> Elem a -> Elem a) -> Int -> FingerTree (Elem a) -> FingerTree (Elem a) #-}
+{-# SPECIALIZE adjustTree :: (Int -> Node a -> Node a) -> Int -> FingerTree (Node a) -> FingerTree (Node a) #-}
+adjustTree      :: Sized a => (Int -> a -> a) ->
+            Int -> FingerTree a -> FingerTree a
+adjustTree _ _ Empty = error "adjustTree of empty tree"
+adjustTree f i (Single x) = Single (f i x)
+adjustTree f i (Deep s pr m sf)
+  | i < spr     = Deep s (adjustDigit f i pr) m sf
+  | i < spm     = Deep s pr (adjustTree (adjustNode f) (i - spr) m) sf
+  | otherwise   = Deep s pr m (adjustDigit f (i - spm) sf)
+  where
+    spr     = size pr
+    spm     = spr + size m
+
+{-# SPECIALIZE adjustNode :: (Int -> Elem a -> Elem a) -> Int -> Node (Elem a) -> Node (Elem a) #-}
+{-# SPECIALIZE adjustNode :: (Int -> Node a -> Node a) -> Int -> Node (Node a) -> Node (Node a) #-}
+adjustNode      :: Sized a => (Int -> a -> a) -> Int -> Node a -> Node a
+adjustNode f i (Node2 s a b)
+  | i < sa      = Node2 s (f i a) b
+  | otherwise   = Node2 s a (f (i - sa) b)
+  where
+    sa      = size a
+adjustNode f i (Node3 s a b c)
+  | i < sa      = Node3 s (f i a) b c
+  | i < sab     = Node3 s a (f (i - sa) b) c
+  | otherwise   = Node3 s a b (f (i - sab) c)
+  where
+    sa      = size a
+    sab     = sa + size b
+
+{-# SPECIALIZE adjustDigit :: (Int -> Elem a -> Elem a) -> Int -> Digit (Elem a) -> Digit (Elem a) #-}
+{-# SPECIALIZE adjustDigit :: (Int -> Node a -> Node a) -> Int -> Digit (Node a) -> Digit (Node a) #-}
+adjustDigit     :: Sized a => (Int -> a -> a) -> Int -> Digit a -> Digit a
+adjustDigit f i (One a) = One (f i a)
+adjustDigit f i (Two a b)
+  | i < sa      = Two (f i a) b
+  | otherwise   = Two a (f (i - sa) b)
+  where
+    sa      = size a
+adjustDigit f i (Three a b c)
+  | i < sa      = Three (f i a) b c
+  | i < sab     = Three a (f (i - sa) b) c
+  | otherwise   = Three a b (f (i - sab) c)
+  where
+    sa      = size a
+    sab     = sa + size b
+adjustDigit f i (Four a b c d)
+  | i < sa      = Four (f i a) b c d
+  | i < sab     = Four a (f (i - sa) b) c d
+  | i < sabc    = Four a b (f (i - sab) c) d
+  | otherwise   = Four a b c (f (i- sabc) d)
+  where
+    sa      = size a
+    sab     = sa + size b
+    sabc    = sab + size c
+
+-- | A generalization of 'fmap', 'mapWithIndex' takes a mapping function
+-- that also depends on the element's index, and applies it to every
+-- element in the sequence.
+mapWithIndex :: (Int -> a -> b) -> Seq a -> Seq b
+mapWithIndex f xs = snd (mapAccumL' (\ i x -> (i + 1, f i x)) 0 xs)
+
+-- Splitting
+
+-- | /O(log(min(i,n-i)))/. The first @i@ elements of a sequence.
+-- If @i@ is negative, @'take' i s@ yields the empty sequence.
+-- If the sequence contains fewer than @i@ elements, the whole sequence
+-- is returned.
+take            :: Int -> Seq a -> Seq a
+take i          =  fst . splitAt i
+
+-- | /O(log(min(i,n-i)))/. Elements of a sequence after the first @i@.
+-- If @i@ is negative, @'drop' i s@ yields the whole sequence.
+-- If the sequence contains fewer than @i@ elements, the empty sequence
+-- is returned.
+drop            :: Int -> Seq a -> Seq a
+drop i          =  snd . splitAt i
+
+-- | /O(log(min(i,n-i)))/. Split a sequence at a given position.
+-- @'splitAt' i s = ('take' i s, 'drop' i s)@.
+splitAt                 :: Int -> Seq a -> (Seq a, Seq a)
+splitAt i (Seq xs)      =  (Seq l, Seq r)
+  where (l, r)          =  split i xs
+
+split :: Int -> FingerTree (Elem a) ->
+    (FingerTree (Elem a), FingerTree (Elem a))
+split i Empty   = i `seq` (Empty, Empty)
+split i xs
+  | size xs > i = (l, consTree x r)
+  | otherwise   = (xs, Empty)
+  where Split l x r = splitTree i xs
+
+data Split t a = Split t a t
+#if TESTING
+    deriving Show
+#endif
+
+{-# SPECIALIZE splitTree :: Int -> FingerTree (Elem a) -> Split (FingerTree (Elem a)) (Elem a) #-}
+{-# SPECIALIZE splitTree :: Int -> FingerTree (Node a) -> Split (FingerTree (Node a)) (Node a) #-}
+splitTree :: Sized a => Int -> FingerTree a -> Split (FingerTree a) a
+splitTree _ Empty = error "splitTree of empty tree"
+splitTree i (Single x) = i `seq` Split Empty x Empty
+splitTree i (Deep _ pr m sf)
+  | i < spr     = case splitDigit i pr of
+            Split l x r -> Split (maybe Empty digitToTree l) x (deepL r m sf)
+  | i < spm     = case splitTree im m of
+            Split ml xs mr -> case splitNode (im - size ml) xs of
+                Split l x r -> Split (deepR pr ml l) x (deepL r mr sf)
+  | otherwise   = case splitDigit (i - spm) sf of
+            Split l x r -> Split (deepR pr m l) x (maybe Empty digitToTree r)
+  where
+    spr     = size pr
+    spm     = spr + size m
+    im      = i - spr
+
+{-# SPECIALIZE splitNode :: Int -> Node (Elem a) -> Split (Maybe (Digit (Elem a))) (Elem a) #-}
+{-# SPECIALIZE splitNode :: Int -> Node (Node a) -> Split (Maybe (Digit (Node a))) (Node a) #-}
+splitNode :: Sized a => Int -> Node a -> Split (Maybe (Digit a)) a
+splitNode i (Node2 _ a b)
+  | i < sa      = Split Nothing a (Just (One b))
+  | otherwise   = Split (Just (One a)) b Nothing
+  where
+    sa      = size a
+splitNode i (Node3 _ a b c)
+  | i < sa      = Split Nothing a (Just (Two b c))
+  | i < sab     = Split (Just (One a)) b (Just (One c))
+  | otherwise   = Split (Just (Two a b)) c Nothing
+  where
+    sa      = size a
+    sab     = sa + size b
+
+{-# SPECIALIZE splitDigit :: Int -> Digit (Elem a) -> Split (Maybe (Digit (Elem a))) (Elem a) #-}
+{-# SPECIALIZE splitDigit :: Int -> Digit (Node a) -> Split (Maybe (Digit (Node a))) (Node a) #-}
+splitDigit :: Sized a => Int -> Digit a -> Split (Maybe (Digit a)) a
+splitDigit i (One a) = i `seq` Split Nothing a Nothing
+splitDigit i (Two a b)
+  | i < sa      = Split Nothing a (Just (One b))
+  | otherwise   = Split (Just (One a)) b Nothing
+  where
+    sa      = size a
+splitDigit i (Three a b c)
+  | i < sa      = Split Nothing a (Just (Two b c))
+  | i < sab     = Split (Just (One a)) b (Just (One c))
+  | otherwise   = Split (Just (Two a b)) c Nothing
+  where
+    sa      = size a
+    sab     = sa + size b
+splitDigit i (Four a b c d)
+  | i < sa      = Split Nothing a (Just (Three b c d))
+  | i < sab     = Split (Just (One a)) b (Just (Two c d))
+  | i < sabc    = Split (Just (Two a b)) c (Just (One d))
+  | otherwise   = Split (Just (Three a b c)) d Nothing
+  where
+    sa      = size a
+    sab     = sa + size b
+    sabc    = sab + size c
+
+-- | /O(n)/.  Returns a sequence of all suffixes of this sequence,
+-- longest first.  For example,
+--
+-- > tails (fromList "abc") = fromList [fromList "abc", fromList "bc", fromList "c", fromList ""]
+--
+-- Evaluating the /i/th suffix takes /O(log(min(i, n-i)))/, but evaluating
+-- every suffix in the sequence takes /O(n)/ due to sharing.
+tails                   :: Seq a -> Seq (Seq a)
+tails (Seq xs)          = Seq (tailsTree (Elem . Seq) xs) |> empty
+
+-- | /O(n)/.  Returns a sequence of all prefixes of this sequence,
+-- shortest first.  For example,
+--
+-- > inits (fromList "abc") = fromList [fromList "", fromList "a", fromList "ab", fromList "abc"]
+--
+-- Evaluating the /i/th prefix takes /O(log(min(i, n-i)))/, but evaluating
+-- every prefix in the sequence takes /O(n)/ due to sharing.
+inits                   :: Seq a -> Seq (Seq a)
+inits (Seq xs)          = empty <| Seq (initsTree (Elem . Seq) xs)
+
+-- This implementation of tails (and, analogously, inits) has the
+-- following algorithmic advantages:
+--      Evaluating each tail in the sequence takes linear total time,
+--      which is better than we could say for
+--              @fromList [drop n xs | n <- [0..length xs]]@.
+--      Evaluating any individual tail takes logarithmic time, which is
+--      better than we can say for either
+--              @scanr (<|) empty xs@ or @iterateN (length xs + 1) (\ xs -> let _ :< xs' = viewl xs in xs') xs@.
+--
+-- Moreover, if we actually look at every tail in the sequence, the
+-- following benchmarks demonstrate that this implementation is modestly
+-- faster than any of the above:
+--
+-- Times (ms)
+--               min      mean    +/-sd    median    max
+-- Seq.tails:   21.986   24.961   10.169   22.417   86.485
+-- scanr:       85.392   87.942    2.488   87.425  100.217
+-- iterateN:       29.952   31.245    1.574   30.412   37.268
+--
+-- The algorithm for tails (and, analogously, inits) is as follows:
+--
+-- A Node in the FingerTree of tails is constructed by evaluating the
+-- corresponding tail of the FingerTree of Nodes, considering the first
+-- Node in this tail, and constructing a Node in which each tail of this
+-- Node is made to be the prefix of the remaining tree.  This ends up
+-- working quite elegantly, as the remainder of the tail of the FingerTree
+-- of Nodes becomes the middle of a new tail, the suffix of the Node is
+-- the prefix, and the suffix of the original tree is retained.
+--
+-- In particular, evaluating the /i/th tail involves making as
+-- many partial evaluations as the Node depth of the /i/th element.
+-- In addition, when we evaluate the /i/th tail, and we also evaluate
+-- the /j/th tail, and /m/ Nodes are on the path to both /i/ and /j/,
+-- each of those /m/ evaluations are shared between the computation of
+-- the /i/th and /j/th tails.
+--
+-- wasserman.louis@gmail.com, 7/16/09
+
+tailsDigit :: Digit a -> Digit (Digit a)
+tailsDigit (One a) = One (One a)
+tailsDigit (Two a b) = Two (Two a b) (One b)
+tailsDigit (Three a b c) = Three (Three a b c) (Two b c) (One c)
+tailsDigit (Four a b c d) = Four (Four a b c d) (Three b c d) (Two c d) (One d)
+
+initsDigit :: Digit a -> Digit (Digit a)
+initsDigit (One a) = One (One a)
+initsDigit (Two a b) = Two (One a) (Two a b)
+initsDigit (Three a b c) = Three (One a) (Two a b) (Three a b c)
+initsDigit (Four a b c d) = Four (One a) (Two a b) (Three a b c) (Four a b c d)
+
+tailsNode :: Node a -> Node (Digit a)
+tailsNode (Node2 s a b) = Node2 s (Two a b) (One b)
+tailsNode (Node3 s a b c) = Node3 s (Three a b c) (Two b c) (One c)
+
+initsNode :: Node a -> Node (Digit a)
+initsNode (Node2 s a b) = Node2 s (One a) (Two a b)
+initsNode (Node3 s a b c) = Node3 s (One a) (Two a b) (Three a b c)
+
+{-# SPECIALIZE tailsTree :: (FingerTree (Elem a) -> Elem b) -> FingerTree (Elem a) -> FingerTree (Elem b) #-}
+{-# SPECIALIZE tailsTree :: (FingerTree (Node a) -> Node b) -> FingerTree (Node a) -> FingerTree (Node b) #-}
+-- | Given a function to apply to tails of a tree, applies that function
+-- to every tail of the specified tree.
+tailsTree :: (Sized a, Sized b) => (FingerTree a -> b) -> FingerTree a -> FingerTree b
+tailsTree _ Empty = Empty
+tailsTree f (Single x) = Single (f (Single x))
+tailsTree f (Deep n pr m sf) =
+    Deep n (fmap (\ pr' -> f (deep pr' m sf)) (tailsDigit pr))
+        (tailsTree f' m)
+        (fmap (f . digitToTree) (tailsDigit sf))
+  where
+    f' ms = let Just2 node m' = viewLTree ms in
+        fmap (\ pr' -> f (deep pr' m' sf)) (tailsNode node)
+
+{-# SPECIALIZE initsTree :: (FingerTree (Elem a) -> Elem b) -> FingerTree (Elem a) -> FingerTree (Elem b) #-}
+{-# SPECIALIZE initsTree :: (FingerTree (Node a) -> Node b) -> FingerTree (Node a) -> FingerTree (Node b) #-}
+-- | Given a function to apply to inits of a tree, applies that function
+-- to every init of the specified tree.
+initsTree :: (Sized a, Sized b) => (FingerTree a -> b) -> FingerTree a -> FingerTree b
+initsTree _ Empty = Empty
+initsTree f (Single x) = Single (f (Single x))
+initsTree f (Deep n pr m sf) =
+    Deep n (fmap (f . digitToTree) (initsDigit pr))
+        (initsTree f' m)
+        (fmap (f . deep pr m) (initsDigit sf))
+  where
+    f' ms =  let Just2 m' node = viewRTree ms in
+             fmap (\ sf' -> f (deep pr m' sf')) (initsNode node)
+
+{-# INLINE foldlWithIndex #-}
+-- | 'foldlWithIndex' is a version of 'foldl' that also provides access
+-- to the index of each element.
+foldlWithIndex :: (b -> Int -> a -> b) -> b -> Seq a -> b
+foldlWithIndex f z xs = foldl (\ g x i -> i `seq` f (g (i - 1)) i x) (const z) xs (length xs - 1)
+
+{-# INLINE foldrWithIndex #-}
+-- | 'foldrWithIndex' is a version of 'foldr' that also provides access
+-- to the index of each element.
+foldrWithIndex :: (Int -> a -> b -> b) -> b -> Seq a -> b
+foldrWithIndex f z xs = foldr (\ x g i -> i `seq` f i x (g (i+1))) (const z) xs 0
+
+{-# INLINE listToMaybe' #-}
+-- 'listToMaybe\'' is a good consumer version of 'listToMaybe'.
+listToMaybe' :: [a] -> Maybe a
+listToMaybe' = foldr (\ x _ -> Just x) Nothing
+
+-- | /O(i)/ where /i/ is the prefix length.  'takeWhileL', applied
+-- to a predicate @p@ and a sequence @xs@, returns the longest prefix
+-- (possibly empty) of @xs@ of elements that satisfy @p@.
+takeWhileL :: (a -> Bool) -> Seq a -> Seq a
+takeWhileL p = fst . spanl p
+
+-- | /O(i)/ where /i/ is the suffix length.  'takeWhileR', applied
+-- to a predicate @p@ and a sequence @xs@, returns the longest suffix
+-- (possibly empty) of @xs@ of elements that satisfy @p@.
+--
+-- @'takeWhileR' p xs@ is equivalent to @'reverse' ('takeWhileL' p ('reverse' xs))@.
+takeWhileR :: (a -> Bool) -> Seq a -> Seq a
+takeWhileR p = fst . spanr p
+
+-- | /O(i)/ where /i/ is the prefix length.  @'dropWhileL' p xs@ returns
+-- the suffix remaining after @'takeWhileL' p xs@.
+dropWhileL :: (a -> Bool) -> Seq a -> Seq a
+dropWhileL p = snd . spanl p
+
+-- | /O(i)/ where /i/ is the suffix length.  @'dropWhileR' p xs@ returns
+-- the prefix remaining after @'takeWhileR' p xs@.
+--
+-- @'dropWhileR' p xs@ is equivalent to @'reverse' ('dropWhileL' p ('reverse' xs))@.
+dropWhileR :: (a -> Bool) -> Seq a -> Seq a
+dropWhileR p = snd . spanr p
+
+-- | /O(i)/ where /i/ is the prefix length.  'spanl', applied to
+-- a predicate @p@ and a sequence @xs@, returns a pair whose first
+-- element is the longest prefix (possibly empty) of @xs@ of elements that
+-- satisfy @p@ and the second element is the remainder of the sequence.
+spanl :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+spanl p = breakl (not . p)
+
+-- | /O(i)/ where /i/ is the suffix length.  'spanr', applied to a
+-- predicate @p@ and a sequence @xs@, returns a pair whose /first/ element
+-- is the longest /suffix/ (possibly empty) of @xs@ of elements that
+-- satisfy @p@ and the second element is the remainder of the sequence.
+spanr :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+spanr p = breakr (not . p)
+
+{-# INLINE breakl #-}
+-- | /O(i)/ where /i/ is the breakpoint index.  'breakl', applied to a
+-- predicate @p@ and a sequence @xs@, returns a pair whose first element
+-- is the longest prefix (possibly empty) of @xs@ of elements that
+-- /do not satisfy/ @p@ and the second element is the remainder of
+-- the sequence.
+--
+-- @'breakl' p@ is equivalent to @'spanl' (not . p)@.
+breakl :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+breakl p xs = foldr (\ i _ -> splitAt i xs) (xs, empty) (findIndicesL p xs)
+
+{-# INLINE breakr #-}
+-- | @'breakr' p@ is equivalent to @'spanr' (not . p)@.
+breakr :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+breakr p xs = foldr (\ i _ -> flipPair (splitAt (i + 1) xs)) (xs, empty) (findIndicesR p xs)
+  where flipPair (x, y) = (y, x)
+
+-- | /O(n)/.  The 'partition' function takes a predicate @p@ and a
+-- sequence @xs@ and returns sequences of those elements which do and
+-- do not satisfy the predicate.
+partition :: (a -> Bool) -> Seq a -> (Seq a, Seq a)
+partition p = foldl part (empty, empty)
+  where
+    part (xs, ys) x
+      | p x         = (xs |> x, ys)
+      | otherwise   = (xs, ys |> x)
+
+-- | /O(n)/.  The 'filter' function takes a predicate @p@ and a sequence
+-- @xs@ and returns a sequence of those elements which satisfy the
+-- predicate.
+filter :: (a -> Bool) -> Seq a -> Seq a
+filter p = foldl (\ xs x -> if p x then xs |> x else xs) empty
+
+-- Indexing sequences
+
+-- | 'elemIndexL' finds the leftmost index of the specified element,
+-- if it is present, and otherwise 'Nothing'.
+elemIndexL :: Eq a => a -> Seq a -> Maybe Int
+elemIndexL x = findIndexL (x ==)
+
+-- | 'elemIndexR' finds the rightmost index of the specified element,
+-- if it is present, and otherwise 'Nothing'.
+elemIndexR :: Eq a => a -> Seq a -> Maybe Int
+elemIndexR x = findIndexR (x ==)
+
+-- | 'elemIndicesL' finds the indices of the specified element, from
+-- left to right (i.e. in ascending order).
+elemIndicesL :: Eq a => a -> Seq a -> [Int]
+elemIndicesL x = findIndicesL (x ==)
+
+-- | 'elemIndicesR' finds the indices of the specified element, from
+-- right to left (i.e. in descending order).
+elemIndicesR :: Eq a => a -> Seq a -> [Int]
+elemIndicesR x = findIndicesR (x ==)
+
+-- | @'findIndexL' p xs@ finds the index of the leftmost element that
+-- satisfies @p@, if any exist.
+findIndexL :: (a -> Bool) -> Seq a -> Maybe Int
+findIndexL p = listToMaybe' . findIndicesL p
+
+-- | @'findIndexR' p xs@ finds the index of the rightmost element that
+-- satisfies @p@, if any exist.
+findIndexR :: (a -> Bool) -> Seq a -> Maybe Int
+findIndexR p = listToMaybe' . findIndicesR p
+
+{-# INLINE findIndicesL #-}
+-- | @'findIndicesL' p@ finds all indices of elements that satisfy @p@,
+-- in ascending order.
+findIndicesL :: (a -> Bool) -> Seq a -> [Int]
+#if __GLASGOW_HASKELL__
+findIndicesL p xs = build (\ c n -> let g i x z = if p x then c i z else z in
+                foldrWithIndex g n xs)
+#else
+findIndicesL p xs = foldrWithIndex g [] xs
+  where g i x is = if p x then i:is else is
+#endif
+
+{-# INLINE findIndicesR #-}
+-- | @'findIndicesR' p@ finds all indices of elements that satisfy @p@,
+-- in descending order.
+findIndicesR :: (a -> Bool) -> Seq a -> [Int]
+#if __GLASGOW_HASKELL__
+findIndicesR p xs = build (\ c n ->
+    let g z i x = if p x then c i z else z in foldlWithIndex g n xs)
+#else
+findIndicesR p xs = foldlWithIndex g [] xs
+  where g is i x = if p x then i:is else is
+#endif
+
+------------------------------------------------------------------------
+-- Lists
+------------------------------------------------------------------------
+
+-- | /O(n)/. Create a sequence from a finite list of elements.
+-- There is a function 'toList' in the opposite direction for all
+-- instances of the 'Foldable' class, including 'Seq'.
+fromList        :: [a] -> Seq a
+fromList        =  Data.List.foldl' (|>) empty
+
+------------------------------------------------------------------------
+-- Reverse
+------------------------------------------------------------------------
+
+-- | /O(n)/. The reverse of a sequence.
+reverse :: Seq a -> Seq a
+reverse (Seq xs) = Seq (reverseTree id xs)
+
+reverseTree :: (a -> a) -> FingerTree a -> FingerTree a
+reverseTree _ Empty = Empty
+reverseTree f (Single x) = Single (f x)
+reverseTree f (Deep s pr m sf) =
+    Deep s (reverseDigit f sf)
+        (reverseTree (reverseNode f) m)
+        (reverseDigit f pr)
+
+{-# INLINE reverseDigit #-}
+reverseDigit :: (a -> a) -> Digit a -> Digit a
+reverseDigit f (One a) = One (f a)
+reverseDigit f (Two a b) = Two (f b) (f a)
+reverseDigit f (Three a b c) = Three (f c) (f b) (f a)
+reverseDigit f (Four a b c d) = Four (f d) (f c) (f b) (f a)
+
+reverseNode :: (a -> a) -> Node a -> Node a
+reverseNode f (Node2 s a b) = Node2 s (f b) (f a)
+reverseNode f (Node3 s a b c) = Node3 s (f c) (f b) (f a)
+
+------------------------------------------------------------------------
+-- Zipping
+------------------------------------------------------------------------
+
+-- | /O(min(n1,n2))/.  'zip' takes two sequences and returns a sequence
+-- of corresponding pairs.  If one input is short, excess elements are
+-- discarded from the right end of the longer sequence.
+zip :: Seq a -> Seq b -> Seq (a, b)
+zip = zipWith (,)
+
+-- | /O(min(n1,n2))/.  'zipWith' generalizes 'zip' by zipping with the
+-- function given as the first argument, instead of a tupling function.
+-- For example, @zipWith (+)@ is applied to two sequences to take the
+-- sequence of corresponding sums.
+zipWith :: (a -> b -> c) -> Seq a -> Seq b -> Seq c
+zipWith f xs ys
+  | length xs <= length ys      = zipWith' f xs ys
+  | otherwise                   = zipWith' (flip f) ys xs
+
+-- like 'zipWith', but assumes length xs <= length ys
+zipWith' :: (a -> b -> c) -> Seq a -> Seq b -> Seq c
+zipWith' f xs ys = snd (mapAccumL k ys xs)
+  where
+    k kys x = case viewl kys of
+           (z :< zs) -> (zs, f x z)
+           EmptyL    -> error "zipWith': unexpected EmptyL"
+
+-- | /O(min(n1,n2,n3))/.  'zip3' takes three sequences and returns a
+-- sequence of triples, analogous to 'zip'.
+zip3 :: Seq a -> Seq b -> Seq c -> Seq (a,b,c)
+zip3 = zipWith3 (,,)
+
+-- | /O(min(n1,n2,n3))/.  'zipWith3' takes a function which combines
+-- three elements, as well as three sequences and returns a sequence of
+-- their point-wise combinations, analogous to 'zipWith'.
+zipWith3 :: (a -> b -> c -> d) -> Seq a -> Seq b -> Seq c -> Seq d
+zipWith3 f s1 s2 s3 = zipWith ($) (zipWith f s1 s2) s3
+
+-- | /O(min(n1,n2,n3,n4))/.  'zip4' takes four sequences and returns a
+-- sequence of quadruples, analogous to 'zip'.
+zip4 :: Seq a -> Seq b -> Seq c -> Seq d -> Seq (a,b,c,d)
+zip4 = zipWith4 (,,,)
+
+-- | /O(min(n1,n2,n3,n4))/.  'zipWith4' takes a function which combines
+-- four elements, as well as four sequences and returns a sequence of
+-- their point-wise combinations, analogous to 'zipWith'.
+zipWith4 :: (a -> b -> c -> d -> e) -> Seq a -> Seq b -> Seq c -> Seq d -> Seq e
+zipWith4 f s1 s2 s3 s4 = zipWith ($) (zipWith ($) (zipWith f s1 s2) s3) s4
+
+------------------------------------------------------------------------
+-- Sorting
+--
+-- sort and sortBy are implemented by simple deforestations of
+--      \ xs -> fromList2 (length xs) . Data.List.sortBy cmp . toList
+-- which does not get deforested automatically, it would appear.
+--
+-- Unstable sorting is performed by a heap sort implementation based on
+-- pairing heaps.  Because the internal structure of sequences is quite
+-- varied, it is difficult to get blocks of elements of roughly the same
+-- length, which would improve merge sort performance.  Pairing heaps,
+-- on the other hand, are relatively resistant to the effects of merging
+-- heaps of wildly different sizes, as guaranteed by its amortized
+-- constant-time merge operation.  Moreover, extensive use of SpecConstr
+-- transformations can be done on pairing heaps, especially when we're
+-- only constructing them to immediately be unrolled.
+--
+-- On purely random sequences of length 50000, with no RTS options,
+-- I get the following statistics, in which heapsort is about 42.5%
+-- faster:  (all comparisons done with -O2)
+--
+-- Times (ms)            min      mean    +/-sd    median    max
+-- to/from list:       103.802  108.572    7.487  106.436  143.339
+-- unstable heapsort:   60.686   62.968    4.275   61.187   79.151
+--
+-- Heapsort, it would seem, is less of a memory hog than Data.List.sortBy.
+-- The gap is narrowed when more memory is available, but heapsort still
+-- wins, 15% faster, with +RTS -H128m:
+--
+-- Times (ms)            min    mean    +/-sd  median    max
+-- to/from list:       42.692  45.074   2.596  44.600  56.601
+-- unstable heapsort:  37.100  38.344   3.043  37.715  55.526
+--
+-- In addition, on strictly increasing sequences the gap is even wider
+-- than normal; heapsort is 68.5% faster with no RTS options:
+-- Times (ms)            min    mean    +/-sd  median    max
+-- to/from list:       52.236  53.574   1.987  53.034  62.098
+-- unstable heapsort:  16.433  16.919   0.931  16.681  21.622
+--
+-- This may be attributed to the elegant nature of the pairing heap.
+--
+-- wasserman.louis@gmail.com, 7/20/09
+------------------------------------------------------------------------
+
+-- | /O(n log n)/.  'sort' sorts the specified 'Seq' by the natural
+-- ordering of its elements.  The sort is stable.
+-- If stability is not required, 'unstableSort' can be considerably
+-- faster, and in particular uses less memory.
+sort :: Ord a => Seq a -> Seq a
+sort = sortBy compare
+
+-- | /O(n log n)/.  'sortBy' sorts the specified 'Seq' according to the
+-- specified comparator.  The sort is stable.
+-- If stability is not required, 'unstableSortBy' can be considerably
+-- faster, and in particular uses less memory.
+sortBy :: (a -> a -> Ordering) -> Seq a -> Seq a
+sortBy cmp xs = fromList2 (length xs) (Data.List.sortBy cmp (toList xs))
+
+-- | /O(n log n)/.  'unstableSort' sorts the specified 'Seq' by
+-- the natural ordering of its elements, but the sort is not stable.
+-- This algorithm is frequently faster and uses less memory than 'sort',
+-- and performs extremely well -- frequently twice as fast as 'sort' --
+-- when the sequence is already nearly sorted.
+unstableSort :: Ord a => Seq a -> Seq a
+unstableSort = unstableSortBy compare
+
+-- | /O(n log n)/.  A generalization of 'unstableSort', 'unstableSortBy'
+-- takes an arbitrary comparator and sorts the specified sequence.
+-- The sort is not stable.  This algorithm is frequently faster and
+-- uses less memory than 'sortBy', and performs extremely well --
+-- frequently twice as fast as 'sortBy' -- when the sequence is already
+-- nearly sorted.
+unstableSortBy :: (a -> a -> Ordering) -> Seq a -> Seq a
+unstableSortBy cmp (Seq xs) =
+    fromList2 (size xs) $ maybe [] (unrollPQ cmp) $
+        toPQ cmp (\ (Elem x) -> PQueue x Nil) xs
+
+-- | fromList2, given a list and its length, constructs a completely
+-- balanced Seq whose elements are that list using the applicativeTree
+-- generalization.
+fromList2 :: Int -> [a] -> Seq a
+fromList2 n = execState (replicateA n (State ht))
+  where
+    ht (x:xs) = (xs, x)
+    ht []     = error "fromList2: short list"
+
+-- | A 'PQueue' is a simple pairing heap.
+data PQueue e = PQueue e (PQL e)
+data PQL e = Nil | {-# UNPACK #-} !(PQueue e) :& PQL e
+
+infixr 8 :&
+
+#if TESTING
+
+instance Functor PQueue where
+    fmap f (PQueue x ts) = PQueue (f x) (fmap f ts)
+
+instance Functor PQL where
+    fmap f (q :& qs) = fmap f q :& fmap f qs
+    fmap _ Nil = Nil
+
+instance Show e => Show (PQueue e) where
+    show = unlines . draw . fmap show
+
+-- borrowed wholesale from Data.Tree, as Data.Tree actually depends
+-- on Data.Sequence
+draw :: PQueue String -> [String]
+draw (PQueue x ts0) = x : drawSubTrees ts0
+  where
+    drawSubTrees Nil = []
+    drawSubTrees (t :& Nil) =
+        "|" : shift "`- " "   " (draw t)
+    drawSubTrees (t :& ts) =
+        "|" : shift "+- " "|  " (draw t) ++ drawSubTrees ts
+
+    shift first other = Data.List.zipWith (++) (first : repeat other)
+#endif
+
+-- | 'unrollPQ', given a comparator function, unrolls a 'PQueue' into
+-- a sorted list.
+unrollPQ :: (e -> e -> Ordering) -> PQueue e -> [e]
+unrollPQ cmp = unrollPQ'
+  where
+    {-# INLINE unrollPQ' #-}
+    unrollPQ' (PQueue x ts) = x:mergePQs0 ts
+    (<>) = mergePQ cmp
+    mergePQs0 Nil = []
+    mergePQs0 (t :& Nil) = unrollPQ' t
+    mergePQs0 (t1 :& t2 :& ts) = mergePQs (t1 <> t2) ts
+    mergePQs t ts = t `seq` case ts of
+        Nil             -> unrollPQ' t
+        t1 :& Nil       -> unrollPQ' (t <> t1)
+        t1 :& t2 :& ts' -> mergePQs (t <> (t1 <> t2)) ts'
+
+-- | 'toPQ', given an ordering function and a mechanism for queueifying
+-- elements, converts a 'FingerTree' to a 'PQueue'.
+toPQ :: (e -> e -> Ordering) -> (a -> PQueue e) -> FingerTree a -> Maybe (PQueue e)
+toPQ _ _ Empty = Nothing
+toPQ _ f (Single x) = Just (f x)
+toPQ cmp f (Deep _ pr m sf) = Just (maybe (pr' <> sf') ((pr' <> sf') <>) (toPQ cmp fNode m))
+  where
+    fDigit digit = case fmap f digit of
+        One a           -> a
+        Two a b         -> a <> b
+        Three a b c     -> a <> b <> c
+        Four a b c d    -> (a <> b) <> (c <> d)
+    (<>) = mergePQ cmp
+    fNode = fDigit . nodeToDigit
+    pr' = fDigit pr
+    sf' = fDigit sf
+
+-- | 'mergePQ' merges two 'PQueue's.
+mergePQ :: (a -> a -> Ordering) -> PQueue a -> PQueue a -> PQueue a
+mergePQ cmp q1@(PQueue x1 ts1) q2@(PQueue x2 ts2)
+  | cmp x1 x2 == GT     = PQueue x2 (q1 :& ts2)
+  | otherwise           = PQueue x1 (q2 :& ts1)
diff --git a/Data/Set.hs b/Data/Set.hs
new file mode 100644
--- /dev/null
+++ b/Data/Set.hs
@@ -0,0 +1,151 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Safe #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Set
+-- Copyright   :  (c) Daan Leijen 2002
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of sets.
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.Set (Set)
+-- >  import qualified Data.Set as Set
+--
+-- The implementation of 'Set' is based on /size balanced/ binary trees (or
+-- trees of /bounded balance/) as described by:
+--
+--    * Stephen Adams, \"/Efficient sets: a balancing act/\",
+--      Journal of Functional Programming 3(4):553-562, October 1993,
+--      <http://www.swiss.ai.mit.edu/~adams/BB/>.
+--
+--    * J. Nievergelt and E.M. Reingold,
+--      \"/Binary search trees of bounded balance/\",
+--      SIAM journal of computing 2(1), March 1973.
+--
+-- Note that the implementation is /left-biased/ -- the elements of a
+-- first argument are always preferred to the second, for example in
+-- 'union' or 'insert'.  Of course, left-biasing can only be observed
+-- when equality is an equivalence relation instead of structural
+-- equality.
+-----------------------------------------------------------------------------
+
+module Data.Set (
+            -- * Strictness properties
+            -- $strictness
+
+            -- * Set type
+#if !defined(TESTING)
+              Set          -- instance Eq,Ord,Show,Read,Data,Typeable
+#else
+              Set(..)
+#endif
+
+            -- * Operators
+            , (\\)
+
+            -- * Query
+            , S.null
+            , size
+            , member
+            , notMember
+            , lookupLT
+            , lookupGT
+            , lookupLE
+            , lookupGE
+            , isSubsetOf
+            , isProperSubsetOf
+
+            -- * Construction
+            , empty
+            , singleton
+            , insert
+            , delete
+
+            -- * Combine
+            , union
+            , unions
+            , difference
+            , intersection
+
+            -- * Filter
+            , S.filter
+            , partition
+            , split
+            , splitMember
+            , splitRoot
+
+            -- * Indexed
+            , lookupIndex
+            , findIndex
+            , elemAt
+            , deleteAt
+
+            -- * Map
+            , S.map
+            , mapMonotonic
+
+            -- * Folds
+            , S.foldr
+            , S.foldl
+            -- ** Strict folds
+            , foldr'
+            , foldl'
+            -- ** Legacy folds
+            , fold
+
+            -- * Min\/Max
+            , findMin
+            , findMax
+            , deleteMin
+            , deleteMax
+            , deleteFindMin
+            , deleteFindMax
+            , maxView
+            , minView
+
+            -- * Conversion
+
+            -- ** List
+            , elems
+            , toList
+            , fromList
+
+            -- ** Ordered list
+            , toAscList
+            , toDescList
+            , fromAscList
+            , fromDistinctAscList
+
+            -- * Debugging
+            , showTree
+            , showTreeWith
+            , valid
+
+#if defined(TESTING)
+            -- Internals (for testing)
+            , bin
+            , balanced
+            , link
+            , merge
+#endif
+            ) where
+
+import Data.Set.Base as S
+
+-- $strictness
+--
+-- This module satisfies the following strictness property:
+--
+-- * Key arguments are evaluated to WHNF
+--
+-- Here are some examples that illustrate the property:
+--
+-- > delete undefined s  ==  undefined
diff --git a/Data/Set/Base.hs b/Data/Set/Base.hs
new file mode 100644
--- /dev/null
+++ b/Data/Set/Base.hs
@@ -0,0 +1,1587 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE DeriveDataTypeable, StandaloneDeriving #-}
+#endif
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 708
+{-# LANGUAGE RoleAnnotations #-}
+{-# LANGUAGE TypeFamilies #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Set.Base
+-- Copyright   :  (c) Daan Leijen 2002
+-- License     :  BSD-style
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- An efficient implementation of sets.
+--
+-- These modules are intended to be imported qualified, to avoid name
+-- clashes with Prelude functions, e.g.
+--
+-- >  import Data.Set (Set)
+-- >  import qualified Data.Set as Set
+--
+-- The implementation of 'Set' is based on /size balanced/ binary trees (or
+-- trees of /bounded balance/) as described by:
+--
+--    * Stephen Adams, \"/Efficient sets: a balancing act/\",
+--      Journal of Functional Programming 3(4):553-562, October 1993,
+--      <http://www.swiss.ai.mit.edu/~adams/BB/>.
+--
+--    * J. Nievergelt and E.M. Reingold,
+--      \"/Binary search trees of bounded balance/\",
+--      SIAM journal of computing 2(1), March 1973.
+--
+-- Note that the implementation is /left-biased/ -- the elements of a
+-- first argument are always preferred to the second, for example in
+-- 'union' or 'insert'.  Of course, left-biasing can only be observed
+-- when equality is an equivalence relation instead of structural
+-- equality.
+-----------------------------------------------------------------------------
+
+-- [Note: Using INLINABLE]
+-- ~~~~~~~~~~~~~~~~~~~~~~~
+-- It is crucial to the performance that the functions specialize on the Ord
+-- type when possible. GHC 7.0 and higher does this by itself when it sees th
+-- unfolding of a function -- that is why all public functions are marked
+-- INLINABLE (that exposes the unfolding).
+
+
+-- [Note: Using INLINE]
+-- ~~~~~~~~~~~~~~~~~~~~
+-- For other compilers and GHC pre 7.0, we mark some of the functions INLINE.
+-- We mark the functions that just navigate down the tree (lookup, insert,
+-- delete and similar). That navigation code gets inlined and thus specialized
+-- when possible. There is a price to pay -- code growth. The code INLINED is
+-- therefore only the tree navigation, all the real work (rebalancing) is not
+-- INLINED by using a NOINLINE.
+--
+-- All methods marked INLINE have to be nonrecursive -- a 'go' function doing
+-- the real work is provided.
+
+
+-- [Note: Type of local 'go' function]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- If the local 'go' function uses an Ord class, it sometimes heap-allocates
+-- the Ord dictionary when the 'go' function does not have explicit type.
+-- In that case we give 'go' explicit type. But this slightly decrease
+-- performance, as the resulting 'go' function can float out to top level.
+
+
+-- [Note: Local 'go' functions and capturing]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- As opposed to IntSet, when 'go' function captures an argument, increased
+-- heap-allocation can occur: sometimes in a polymorphic function, the 'go'
+-- floats out of its enclosing function and then it heap-allocates the
+-- dictionary and the argument. Maybe it floats out too late and strictness
+-- analyzer cannot see that these could be passed on stack.
+--
+-- For example, change 'member' so that its local 'go' function is not passing
+-- argument x and then look at the resulting code for hedgeInt.
+
+
+-- [Note: Order of constructors]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- The order of constructors of Set matters when considering performance.
+-- Currently in GHC 7.0, when type has 2 constructors, a forward conditional
+-- jump is made when successfully matching second constructor. Successful match
+-- of first constructor results in the forward jump not taken.
+-- On GHC 7.0, reordering constructors from Tip | Bin to Bin | Tip
+-- improves the benchmark by up to 10% on x86.
+
+module Data.Set.Base (
+            -- * Set type
+              Set(..)       -- instance Eq,Ord,Show,Read,Data,Typeable
+
+            -- * Operators
+            , (\\)
+
+            -- * Query
+            , null
+            , size
+            , member
+            , notMember
+            , lookupLT
+            , lookupGT
+            , lookupLE
+            , lookupGE
+            , isSubsetOf
+            , isProperSubsetOf
+
+            -- * Construction
+            , empty
+            , singleton
+            , insert
+            , delete
+
+            -- * Combine
+            , union
+            , unions
+            , difference
+            , intersection
+
+            -- * Filter
+            , filter
+            , partition
+            , split
+            , splitMember
+            , splitRoot
+
+            -- * Indexed
+            , lookupIndex
+            , findIndex
+            , elemAt
+            , deleteAt
+
+            -- * Map
+            , map
+            , mapMonotonic
+
+            -- * Folds
+            , foldr
+            , foldl
+            -- ** Strict folds
+            , foldr'
+            , foldl'
+            -- ** Legacy folds
+            , fold
+
+            -- * Min\/Max
+            , findMin
+            , findMax
+            , deleteMin
+            , deleteMax
+            , deleteFindMin
+            , deleteFindMax
+            , maxView
+            , minView
+
+            -- * Conversion
+
+            -- ** List
+            , elems
+            , toList
+            , fromList
+
+            -- ** Ordered list
+            , toAscList
+            , toDescList
+            , fromAscList
+            , fromDistinctAscList
+
+            -- * Debugging
+            , showTree
+            , showTreeWith
+            , valid
+
+            -- Internals (for testing)
+            , bin
+            , balanced
+            , link
+            , merge
+            ) where
+
+import Prelude hiding (filter,foldl,foldr,null,map)
+import qualified Data.List as List
+import Data.Bits (shiftL, shiftR)
+import Data.Monoid (Monoid(..))
+import qualified Data.Foldable as Foldable
+import Data.Typeable
+import Control.DeepSeq (NFData(rnf))
+
+import Data.StrictPair
+
+#if __GLASGOW_HASKELL__
+import GHC.Exts ( build )
+#if __GLASGOW_HASKELL__ >= 708
+import qualified GHC.Exts as GHCExts
+#endif
+import Text.Read
+import Data.Data
+#endif
+
+-- Use macros to define strictness of functions.
+-- STRICT_x_OF_y denotes an y-ary function strict in the x-th parameter.
+-- We do not use BangPatterns, because they are not in any standard and we
+-- want the compilers to be compiled by as many compilers as possible.
+#define STRICT_1_OF_2(fn) fn arg _ | arg `seq` False = undefined
+#define STRICT_1_OF_3(fn) fn arg _ _ | arg `seq` False = undefined
+#define STRICT_2_OF_3(fn) fn _ arg _ | arg `seq` False = undefined
+
+{--------------------------------------------------------------------
+  Operators
+--------------------------------------------------------------------}
+infixl 9 \\ --
+
+-- | /O(n+m)/. See 'difference'.
+(\\) :: Ord a => Set a -> Set a -> Set a
+m1 \\ m2 = difference m1 m2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE (\\) #-}
+#endif
+
+{--------------------------------------------------------------------
+  Sets are size balanced trees
+--------------------------------------------------------------------}
+-- | A set of values @a@.
+
+-- See Note: Order of constructors
+data Set a    = Bin {-# UNPACK #-} !Size !a !(Set a) !(Set a)
+              | Tip
+
+type Size     = Int
+
+#if __GLASGOW_HASKELL__ >= 708
+type role Set nominal
+#endif
+
+instance Ord a => Monoid (Set a) where
+    mempty  = empty
+    mappend = union
+    mconcat = unions
+
+instance Foldable.Foldable Set where
+    fold t = go t
+      where go Tip = mempty
+            go (Bin 1 k _ _) = k
+            go (Bin _ k l r) = go l `mappend` (k `mappend` go r)
+    {-# INLINABLE fold #-}
+    foldr = foldr
+    {-# INLINE foldr #-}
+    foldl = foldl
+    {-# INLINE foldl #-}
+    foldMap f t = go t
+      where go Tip = mempty
+            go (Bin 1 k _ _) = f k
+            go (Bin _ k l r) = go l `mappend` (f k `mappend` go r)
+    {-# INLINE foldMap #-}
+
+#if __GLASGOW_HASKELL__
+
+{--------------------------------------------------------------------
+  A Data instance
+--------------------------------------------------------------------}
+
+-- This instance preserves data abstraction at the cost of inefficiency.
+-- We provide limited reflection services for the sake of data abstraction.
+
+instance (Data a, Ord a) => Data (Set a) where
+  gfoldl f z set = z fromList `f` (toList set)
+  toConstr _     = fromListConstr
+  gunfold k z c  = case constrIndex c of
+    1 -> k (z fromList)
+    _ -> error "gunfold"
+  dataTypeOf _   = setDataType
+  dataCast1 f    = gcast1 f
+
+fromListConstr :: Constr
+fromListConstr = mkConstr setDataType "fromList" [] Prefix
+
+setDataType :: DataType
+setDataType = mkDataType "Data.Set.Base.Set" [fromListConstr]
+
+#endif
+
+{--------------------------------------------------------------------
+  Query
+--------------------------------------------------------------------}
+-- | /O(1)/. Is this the empty set?
+null :: Set a -> Bool
+null Tip      = True
+null (Bin {}) = False
+{-# INLINE null #-}
+
+-- | /O(1)/. The number of elements in the set.
+size :: Set a -> Int
+size Tip = 0
+size (Bin sz _ _ _) = sz
+{-# INLINE size #-}
+
+-- | /O(log n)/. Is the element in the set?
+member :: Ord a => a -> Set a -> Bool
+member = go
+  where
+    STRICT_1_OF_2(go)
+    go _ Tip = False
+    go x (Bin _ y l r) = case compare x y of
+      LT -> go x l
+      GT -> go x r
+      EQ -> True
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE member #-}
+#else
+{-# INLINE member #-}
+#endif
+
+infix 4 `member`
+
+-- | /O(log n)/. Is the element not in the set?
+notMember :: Ord a => a -> Set a -> Bool
+notMember a t = not $ member a t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE notMember #-}
+#else
+{-# INLINE notMember #-}
+#endif
+
+infix 4 `notMember`
+
+-- | /O(log n)/. Find largest element smaller than the given one.
+--
+-- > lookupLT 3 (fromList [3, 5]) == Nothing
+-- > lookupLT 5 (fromList [3, 5]) == Just 3
+lookupLT :: Ord a => a -> Set a -> Maybe a
+lookupLT = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing x (Bin _ y l r) | x <= y = goNothing x l
+                              | otherwise = goJust x y r
+
+    STRICT_1_OF_3(goJust)
+    goJust _ best Tip = Just best
+    goJust x best (Bin _ y l r) | x <= y = goJust x best l
+                                | otherwise = goJust x y r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupLT #-}
+#else
+{-# INLINE lookupLT #-}
+#endif
+
+-- | /O(log n)/. Find smallest element greater than the given one.
+--
+-- > lookupGT 4 (fromList [3, 5]) == Just 5
+-- > lookupGT 5 (fromList [3, 5]) == Nothing
+lookupGT :: Ord a => a -> Set a -> Maybe a
+lookupGT = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing x (Bin _ y l r) | x < y = goJust x y l
+                              | otherwise = goNothing x r
+
+    STRICT_1_OF_3(goJust)
+    goJust _ best Tip = Just best
+    goJust x best (Bin _ y l r) | x < y = goJust x y l
+                                | otherwise = goJust x best r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupGT #-}
+#else
+{-# INLINE lookupGT #-}
+#endif
+
+-- | /O(log n)/. Find largest element smaller or equal to the given one.
+--
+-- > lookupLE 2 (fromList [3, 5]) == Nothing
+-- > lookupLE 4 (fromList [3, 5]) == Just 3
+-- > lookupLE 5 (fromList [3, 5]) == Just 5
+lookupLE :: Ord a => a -> Set a -> Maybe a
+lookupLE = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing x (Bin _ y l r) = case compare x y of LT -> goNothing x l
+                                                    EQ -> Just y
+                                                    GT -> goJust x y r
+
+    STRICT_1_OF_3(goJust)
+    goJust _ best Tip = Just best
+    goJust x best (Bin _ y l r) = case compare x y of LT -> goJust x best l
+                                                      EQ -> Just y
+                                                      GT -> goJust x y r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupLE #-}
+#else
+{-# INLINE lookupLE #-}
+#endif
+
+-- | /O(log n)/. Find smallest element greater or equal to the given one.
+--
+-- > lookupGE 3 (fromList [3, 5]) == Just 3
+-- > lookupGE 4 (fromList [3, 5]) == Just 5
+-- > lookupGE 6 (fromList [3, 5]) == Nothing
+lookupGE :: Ord a => a -> Set a -> Maybe a
+lookupGE = goNothing
+  where
+    STRICT_1_OF_2(goNothing)
+    goNothing _ Tip = Nothing
+    goNothing x (Bin _ y l r) = case compare x y of LT -> goJust x y l
+                                                    EQ -> Just y
+                                                    GT -> goNothing x r
+
+    STRICT_1_OF_3(goJust)
+    goJust _ best Tip = Just best
+    goJust x best (Bin _ y l r) = case compare x y of LT -> goJust x y l
+                                                      EQ -> Just y
+                                                      GT -> goJust x best r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupGE #-}
+#else
+{-# INLINE lookupGE #-}
+#endif
+
+{--------------------------------------------------------------------
+  Construction
+--------------------------------------------------------------------}
+-- | /O(1)/. The empty set.
+empty  :: Set a
+empty = Tip
+{-# INLINE empty #-}
+
+-- | /O(1)/. Create a singleton set.
+singleton :: a -> Set a
+singleton x = Bin 1 x Tip Tip
+{-# INLINE singleton #-}
+
+{--------------------------------------------------------------------
+  Insertion, Deletion
+--------------------------------------------------------------------}
+-- | /O(log n)/. Insert an element in a set.
+-- If the set already contains an element equal to the given value,
+-- it is replaced with the new value.
+
+-- See Note: Type of local 'go' function
+insert :: Ord a => a -> Set a -> Set a
+insert = go
+  where
+    go :: Ord a => a -> Set a -> Set a
+    STRICT_1_OF_2(go)
+    go x Tip = singleton x
+    go x (Bin sz y l r) = case compare x y of
+        LT -> balanceL y (go x l) r
+        GT -> balanceR y l (go x r)
+        EQ -> Bin sz x l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insert #-}
+#else
+{-# INLINE insert #-}
+#endif
+
+-- Insert an element to the set only if it is not in the set.
+-- Used by `union`.
+
+-- See Note: Type of local 'go' function
+insertR :: Ord a => a -> Set a -> Set a
+insertR = go
+  where
+    go :: Ord a => a -> Set a -> Set a
+    STRICT_1_OF_2(go)
+    go x Tip = singleton x
+    go x t@(Bin _ y l r) = case compare x y of
+        LT -> balanceL y (go x l) r
+        GT -> balanceR y l (go x r)
+        EQ -> t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE insertR #-}
+#else
+{-# INLINE insertR #-}
+#endif
+
+-- | /O(log n)/. Delete an element from a set.
+
+-- See Note: Type of local 'go' function
+delete :: Ord a => a -> Set a -> Set a
+delete = go
+  where
+    go :: Ord a => a -> Set a -> Set a
+    STRICT_1_OF_2(go)
+    go _ Tip = Tip
+    go x (Bin _ y l r) = case compare x y of
+        LT -> balanceR y (go x l) r
+        GT -> balanceL y l (go x r)
+        EQ -> glue l r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE delete #-}
+#else
+{-# INLINE delete #-}
+#endif
+
+{--------------------------------------------------------------------
+  Subset
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Is this a proper subset? (ie. a subset but not equal).
+isProperSubsetOf :: Ord a => Set a -> Set a -> Bool
+isProperSubsetOf s1 s2
+    = (size s1 < size s2) && (isSubsetOf s1 s2)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isProperSubsetOf #-}
+#endif
+
+
+-- | /O(n+m)/. Is this a subset?
+-- @(s1 `isSubsetOf` s2)@ tells whether @s1@ is a subset of @s2@.
+isSubsetOf :: Ord a => Set a -> Set a -> Bool
+isSubsetOf t1 t2
+  = (size t1 <= size t2) && (isSubsetOfX t1 t2)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isSubsetOf #-}
+#endif
+
+isSubsetOfX :: Ord a => Set a -> Set a -> Bool
+isSubsetOfX Tip _ = True
+isSubsetOfX _ Tip = False
+isSubsetOfX (Bin _ x l r) t
+  = found && isSubsetOfX l lt && isSubsetOfX r gt
+  where
+    (lt,found,gt) = splitMember x t
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE isSubsetOfX #-}
+#endif
+
+
+{--------------------------------------------------------------------
+  Minimal, Maximal
+--------------------------------------------------------------------}
+-- | /O(log n)/. The minimal element of a set.
+findMin :: Set a -> a
+findMin (Bin _ x Tip _) = x
+findMin (Bin _ _ l _)   = findMin l
+findMin Tip             = error "Set.findMin: empty set has no minimal element"
+
+-- | /O(log n)/. The maximal element of a set.
+findMax :: Set a -> a
+findMax (Bin _ x _ Tip)  = x
+findMax (Bin _ _ _ r)    = findMax r
+findMax Tip              = error "Set.findMax: empty set has no maximal element"
+
+-- | /O(log n)/. Delete the minimal element. Returns an empty set if the set is empty.
+deleteMin :: Set a -> Set a
+deleteMin (Bin _ _ Tip r) = r
+deleteMin (Bin _ x l r)   = balanceR x (deleteMin l) r
+deleteMin Tip             = Tip
+
+-- | /O(log n)/. Delete the maximal element. Returns an empty set if the set is empty.
+deleteMax :: Set a -> Set a
+deleteMax (Bin _ _ l Tip) = l
+deleteMax (Bin _ x l r)   = balanceL x l (deleteMax r)
+deleteMax Tip             = Tip
+
+{--------------------------------------------------------------------
+  Union.
+--------------------------------------------------------------------}
+-- | The union of a list of sets: (@'unions' == 'foldl' 'union' 'empty'@).
+unions :: Ord a => [Set a] -> Set a
+unions = foldlStrict union empty
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE unions #-}
+#endif
+
+-- | /O(n+m)/. The union of two sets, preferring the first set when
+-- equal elements are encountered.
+-- The implementation uses the efficient /hedge-union/ algorithm.
+union :: Ord a => Set a -> Set a -> Set a
+union Tip t2  = t2
+union t1 Tip  = t1
+union t1 t2 = hedgeUnion NothingS NothingS t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE union #-}
+#endif
+
+infixl 5 `union`
+
+hedgeUnion :: Ord a => MaybeS a -> MaybeS a -> Set a -> Set a -> Set a
+hedgeUnion _   _   t1  Tip = t1
+hedgeUnion blo bhi Tip (Bin _ x l r) = link x (filterGt blo l) (filterLt bhi r)
+hedgeUnion _   _   t1  (Bin _ x Tip Tip) = insertR x t1   -- According to benchmarks, this special case increases
+                                                          -- performance up to 30%. It does not help in difference or intersection.
+hedgeUnion blo bhi (Bin _ x l r) t2 = link x (hedgeUnion blo bmi l (trim blo bmi t2))
+                                             (hedgeUnion bmi bhi r (trim bmi bhi t2))
+  where bmi = JustS x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE hedgeUnion #-}
+#endif
+
+{--------------------------------------------------------------------
+  Difference
+--------------------------------------------------------------------}
+-- | /O(n+m)/. Difference of two sets.
+-- The implementation uses an efficient /hedge/ algorithm comparable with /hedge-union/.
+difference :: Ord a => Set a -> Set a -> Set a
+difference Tip _   = Tip
+difference t1 Tip  = t1
+difference t1 t2   = hedgeDiff NothingS NothingS t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE difference #-}
+#endif
+
+hedgeDiff :: Ord a => MaybeS a -> MaybeS a -> Set a -> Set a -> Set a
+hedgeDiff _   _   Tip           _ = Tip
+hedgeDiff blo bhi (Bin _ x l r) Tip = link x (filterGt blo l) (filterLt bhi r)
+hedgeDiff blo bhi t (Bin _ x l r) = merge (hedgeDiff blo bmi (trim blo bmi t) l)
+                                          (hedgeDiff bmi bhi (trim bmi bhi t) r)
+  where bmi = JustS x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE hedgeDiff #-}
+#endif
+
+{--------------------------------------------------------------------
+  Intersection
+--------------------------------------------------------------------}
+-- | /O(n+m)/. The intersection of two sets.  The implementation uses an
+-- efficient /hedge/ algorithm comparable with /hedge-union/.  Elements of the
+-- result come from the first set, so for example
+--
+-- > import qualified Data.Set as S
+-- > data AB = A | B deriving Show
+-- > instance Ord AB where compare _ _ = EQ
+-- > instance Eq AB where _ == _ = True
+-- > main = print (S.singleton A `S.intersection` S.singleton B,
+-- >               S.singleton B `S.intersection` S.singleton A)
+--
+-- prints @(fromList [A],fromList [B])@.
+intersection :: Ord a => Set a -> Set a -> Set a
+intersection Tip _ = Tip
+intersection _ Tip = Tip
+intersection t1 t2 = hedgeInt NothingS NothingS t1 t2
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE intersection #-}
+#endif
+
+infixl 5 `intersection`
+
+hedgeInt :: Ord a => MaybeS a -> MaybeS a -> Set a -> Set a -> Set a
+hedgeInt _ _ _   Tip = Tip
+hedgeInt _ _ Tip _   = Tip
+hedgeInt blo bhi (Bin _ x l r) t2 = let l' = hedgeInt blo bmi l (trim blo bmi t2)
+                                        r' = hedgeInt bmi bhi r (trim bmi bhi t2)
+                                    in if x `member` t2 then link x l' r' else merge l' r'
+  where bmi = JustS x
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE hedgeInt #-}
+#endif
+
+{--------------------------------------------------------------------
+  Filter and partition
+--------------------------------------------------------------------}
+-- | /O(n)/. Filter all elements that satisfy the predicate.
+filter :: (a -> Bool) -> Set a -> Set a
+filter _ Tip = Tip
+filter p (Bin _ x l r)
+    | p x       = link x (filter p l) (filter p r)
+    | otherwise = merge (filter p l) (filter p r)
+
+-- | /O(n)/. Partition the set into two sets, one with all elements that satisfy
+-- the predicate and one with all elements that don't satisfy the predicate.
+-- See also 'split'.
+partition :: (a -> Bool) -> Set a -> (Set a,Set a)
+partition p0 t0 = toPair $ go p0 t0
+  where
+    go _ Tip = (Tip :*: Tip)
+    go p (Bin _ x l r) = case (go p l, go p r) of
+      ((l1 :*: l2), (r1 :*: r2))
+        | p x       -> link x l1 r1 :*: merge l2 r2
+        | otherwise -> merge l1 r1 :*: link x l2 r2
+
+{----------------------------------------------------------------------
+  Map
+----------------------------------------------------------------------}
+
+-- | /O(n*log n)/.
+-- @'map' f s@ is the set obtained by applying @f@ to each element of @s@.
+--
+-- It's worth noting that the size of the result may be smaller if,
+-- for some @(x,y)@, @x \/= y && f x == f y@
+
+map :: Ord b => (a->b) -> Set a -> Set b
+map f = fromList . List.map f . toList
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE map #-}
+#endif
+
+-- | /O(n)/. The
+--
+-- @'mapMonotonic' f s == 'map' f s@, but works only when @f@ is monotonic.
+-- /The precondition is not checked./
+-- Semi-formally, we have:
+--
+-- > and [x < y ==> f x < f y | x <- ls, y <- ls]
+-- >                     ==> mapMonotonic f s == map f s
+-- >     where ls = toList s
+
+mapMonotonic :: (a->b) -> Set a -> Set b
+mapMonotonic _ Tip = Tip
+mapMonotonic f (Bin sz x l r) = Bin sz (f x) (mapMonotonic f l) (mapMonotonic f r)
+
+{--------------------------------------------------------------------
+  Fold
+--------------------------------------------------------------------}
+-- | /O(n)/. Fold the elements in the set using the given right-associative
+-- binary operator. This function is an equivalent of 'foldr' and is present
+-- for compatibility only.
+--
+-- /Please note that fold will be deprecated in the future and removed./
+fold :: (a -> b -> b) -> b -> Set a -> b
+fold = foldr
+{-# INLINE fold #-}
+
+-- | /O(n)/. Fold the elements in the set using the given right-associative
+-- binary operator, such that @'foldr' f z == 'Prelude.foldr' f z . 'toAscList'@.
+--
+-- For example,
+--
+-- > toAscList set = foldr (:) [] set
+foldr :: (a -> b -> b) -> b -> Set a -> b
+foldr f z = go z
+  where
+    go z' Tip           = z'
+    go z' (Bin _ x l r) = go (f x (go z' r)) l
+{-# INLINE foldr #-}
+
+-- | /O(n)/. A strict version of 'foldr'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldr' :: (a -> b -> b) -> b -> Set a -> b
+foldr' f z = go z
+  where
+    STRICT_1_OF_2(go)
+    go z' Tip           = z'
+    go z' (Bin _ x l r) = go (f x (go z' r)) l
+{-# INLINE foldr' #-}
+
+-- | /O(n)/. Fold the elements in the set using the given left-associative
+-- binary operator, such that @'foldl' f z == 'Prelude.foldl' f z . 'toAscList'@.
+--
+-- For example,
+--
+-- > toDescList set = foldl (flip (:)) [] set
+foldl :: (a -> b -> a) -> a -> Set b -> a
+foldl f z = go z
+  where
+    go z' Tip           = z'
+    go z' (Bin _ x l r) = go (f (go z' l) x) r
+{-# INLINE foldl #-}
+
+-- | /O(n)/. A strict version of 'foldl'. Each application of the operator is
+-- evaluated before using the result in the next application. This
+-- function is strict in the starting value.
+foldl' :: (a -> b -> a) -> a -> Set b -> a
+foldl' f z = go z
+  where
+    STRICT_1_OF_2(go)
+    go z' Tip           = z'
+    go z' (Bin _ x l r) = go (f (go z' l) x) r
+{-# INLINE foldl' #-}
+
+{--------------------------------------------------------------------
+  List variations
+--------------------------------------------------------------------}
+-- | /O(n)/. An alias of 'toAscList'. The elements of a set in ascending order.
+-- Subject to list fusion.
+elems :: Set a -> [a]
+elems = toAscList
+
+{--------------------------------------------------------------------
+  Lists
+--------------------------------------------------------------------}
+#if __GLASGOW_HASKELL__ >= 708
+instance (Ord a) => GHCExts.IsList (Set a) where
+  type Item (Set a) = a
+  fromList = fromList
+  toList   = toList
+#endif
+
+-- | /O(n)/. Convert the set to a list of elements. Subject to list fusion.
+toList :: Set a -> [a]
+toList = toAscList
+
+-- | /O(n)/. Convert the set to an ascending list of elements. Subject to list fusion.
+toAscList :: Set a -> [a]
+toAscList = foldr (:) []
+
+-- | /O(n)/. Convert the set to a descending list of elements. Subject to list
+-- fusion.
+toDescList :: Set a -> [a]
+toDescList = foldl (flip (:)) []
+
+-- List fusion for the list generating functions.
+#if __GLASGOW_HASKELL__
+-- The foldrFB and foldlFB are foldr and foldl equivalents, used for list fusion.
+-- They are important to convert unfused to{Asc,Desc}List back, see mapFB in prelude.
+foldrFB :: (a -> b -> b) -> b -> Set a -> b
+foldrFB = foldr
+{-# INLINE[0] foldrFB #-}
+foldlFB :: (a -> b -> a) -> a -> Set b -> a
+foldlFB = foldl
+{-# INLINE[0] foldlFB #-}
+
+-- Inline elems and toList, so that we need to fuse only toAscList.
+{-# INLINE elems #-}
+{-# INLINE toList #-}
+
+-- The fusion is enabled up to phase 2 included. If it does not succeed,
+-- convert in phase 1 the expanded to{Asc,Desc}List calls back to
+-- to{Asc,Desc}List.  In phase 0, we inline fold{lr}FB (which were used in
+-- a list fusion, otherwise it would go away in phase 1), and let compiler do
+-- whatever it wants with to{Asc,Desc}List -- it was forbidden to inline it
+-- before phase 0, otherwise the fusion rules would not fire at all.
+{-# NOINLINE[0] toAscList #-}
+{-# NOINLINE[0] toDescList #-}
+{-# RULES "Set.toAscList" [~1] forall s . toAscList s = build (\c n -> foldrFB c n s) #-}
+{-# RULES "Set.toAscListBack" [1] foldrFB (:) [] = toAscList #-}
+{-# RULES "Set.toDescList" [~1] forall s . toDescList s = build (\c n -> foldlFB (\xs x -> c x xs) n s) #-}
+{-# RULES "Set.toDescListBack" [1] foldlFB (\xs x -> x : xs) [] = toDescList #-}
+#endif
+
+-- | /O(n*log n)/. Create a set from a list of elements.
+--
+-- If the elemens are ordered, linear-time implementation is used,
+-- with the performance equal to 'fromDistinctAscList'.
+
+-- For some reason, when 'singleton' is used in fromList or in
+-- create, it is not inlined, so we inline it manually.
+fromList :: Ord a => [a] -> Set a
+fromList [] = Tip
+fromList [x] = Bin 1 x Tip Tip
+fromList (x0 : xs0) | not_ordered x0 xs0 = fromList' (Bin 1 x0 Tip Tip) xs0
+                    | otherwise = go (1::Int) (Bin 1 x0 Tip Tip) xs0
+  where
+    not_ordered _ [] = False
+    not_ordered x (y : _) = x >= y
+    {-# INLINE not_ordered #-}
+
+    fromList' t0 xs = foldlStrict ins t0 xs
+      where ins t x = insert x t
+
+    STRICT_1_OF_3(go)
+    go _ t [] = t
+    go _ t [x] = insertMax x t
+    go s l xs@(x : xss) | not_ordered x xss = fromList' l xs
+                        | otherwise = case create s xss of
+                            (r, ys, []) -> go (s `shiftL` 1) (link x l r) ys
+                            (r, _,  ys) -> fromList' (link x l r) ys
+
+    -- The create is returning a triple (tree, xs, ys). Both xs and ys
+    -- represent not yet processed elements and only one of them can be nonempty.
+    -- If ys is nonempty, the keys in ys are not ordered with respect to tree
+    -- and must be inserted using fromList'. Otherwise the keys have been
+    -- ordered so far.
+    STRICT_1_OF_2(create)
+    create _ [] = (Tip, [], [])
+    create s xs@(x : xss)
+      | s == 1 = if not_ordered x xss then (Bin 1 x Tip Tip, [], xss)
+                                      else (Bin 1 x Tip Tip, xss, [])
+      | otherwise = case create (s `shiftR` 1) xs of
+                      res@(_, [], _) -> res
+                      (l, [y], zs) -> (insertMax y l, [], zs)
+                      (l, ys@(y:yss), _) | not_ordered y yss -> (l, [], ys)
+                                         | otherwise -> case create (s `shiftR` 1) yss of
+                                                   (r, zs, ws) -> (link y l r, zs, ws)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromList #-}
+#endif
+
+{--------------------------------------------------------------------
+  Building trees from ascending/descending lists can be done in linear time.
+
+  Note that if [xs] is ascending that:
+    fromAscList xs == fromList xs
+--------------------------------------------------------------------}
+-- | /O(n)/. Build a set from an ascending list in linear time.
+-- /The precondition (input list is ascending) is not checked./
+fromAscList :: Eq a => [a] -> Set a
+fromAscList xs
+  = fromDistinctAscList (combineEq xs)
+  where
+  -- [combineEq xs] combines equal elements with [const] in an ordered list [xs]
+  combineEq xs'
+    = case xs' of
+        []     -> []
+        [x]    -> [x]
+        (x:xx) -> combineEq' x xx
+
+  combineEq' z [] = [z]
+  combineEq' z (x:xs')
+    | z==x      =   combineEq' z xs'
+    | otherwise = z:combineEq' x xs'
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE fromAscList #-}
+#endif
+
+
+-- | /O(n)/. Build a set from an ascending list of distinct elements in linear time.
+-- /The precondition (input list is strictly ascending) is not checked./
+
+-- For some reason, when 'singleton' is used in fromDistinctAscList or in
+-- create, it is not inlined, so we inline it manually.
+fromDistinctAscList :: [a] -> Set a
+fromDistinctAscList [] = Tip
+fromDistinctAscList (x0 : xs0) = go (1::Int) (Bin 1 x0 Tip Tip) xs0
+  where
+    STRICT_1_OF_3(go)
+    go _ t [] = t
+    go s l (x : xs) = case create s xs of
+                        (r, ys) -> go (s `shiftL` 1) (link x l r) ys
+
+    STRICT_1_OF_2(create)
+    create _ [] = (Tip, [])
+    create s xs@(x : xs')
+      | s == 1 = (Bin 1 x Tip Tip, xs')
+      | otherwise = case create (s `shiftR` 1) xs of
+                      res@(_, []) -> res
+                      (l, y:ys) -> case create (s `shiftR` 1) ys of
+                        (r, zs) -> (link y l r, zs)
+
+{--------------------------------------------------------------------
+  Eq converts the set to a list. In a lazy setting, this
+  actually seems one of the faster methods to compare two trees
+  and it is certainly the simplest :-)
+--------------------------------------------------------------------}
+instance Eq a => Eq (Set a) where
+  t1 == t2  = (size t1 == size t2) && (toAscList t1 == toAscList t2)
+
+{--------------------------------------------------------------------
+  Ord
+--------------------------------------------------------------------}
+
+instance Ord a => Ord (Set a) where
+    compare s1 s2 = compare (toAscList s1) (toAscList s2)
+
+{--------------------------------------------------------------------
+  Show
+--------------------------------------------------------------------}
+instance Show a => Show (Set a) where
+  showsPrec p xs = showParen (p > 10) $
+    showString "fromList " . shows (toList xs)
+
+{--------------------------------------------------------------------
+  Read
+--------------------------------------------------------------------}
+instance (Read a, Ord a) => Read (Set a) where
+#ifdef __GLASGOW_HASKELL__
+  readPrec = parens $ prec 10 $ do
+    Ident "fromList" <- lexP
+    xs <- readPrec
+    return (fromList xs)
+
+  readListPrec = readListPrecDefault
+#else
+  readsPrec p = readParen (p > 10) $ \ r -> do
+    ("fromList",s) <- lex r
+    (xs,t) <- reads s
+    return (fromList xs,t)
+#endif
+
+{--------------------------------------------------------------------
+  Typeable/Data
+--------------------------------------------------------------------}
+
+#include "Typeable.h"
+INSTANCE_TYPEABLE1(Set,setTc,"Set")
+
+{--------------------------------------------------------------------
+  NFData
+--------------------------------------------------------------------}
+
+instance NFData a => NFData (Set a) where
+    rnf Tip           = ()
+    rnf (Bin _ y l r) = rnf y `seq` rnf l `seq` rnf r
+
+{--------------------------------------------------------------------
+  Utility functions that return sub-ranges of the original
+  tree. Some functions take a `Maybe value` as an argument to
+  allow comparisons against infinite values. These are called `blow`
+  (Nothing is -\infty) and `bhigh` (here Nothing is +\infty).
+  We use MaybeS value, which is a Maybe strict in the Just case.
+
+  [trim blow bhigh t]   A tree that is either empty or where [x > blow]
+                        and [x < bhigh] for the value [x] of the root.
+  [filterGt blow t]     A tree where for all values [k]. [k > blow]
+  [filterLt bhigh t]    A tree where for all values [k]. [k < bhigh]
+
+  [split k t]           Returns two trees [l] and [r] where all values
+                        in [l] are <[k] and all keys in [r] are >[k].
+  [splitMember k t]     Just like [split] but also returns whether [k]
+                        was found in the tree.
+--------------------------------------------------------------------}
+
+data MaybeS a = NothingS | JustS !a
+
+{--------------------------------------------------------------------
+  [trim blo bhi t] trims away all subtrees that surely contain no
+  values between the range [blo] to [bhi]. The returned tree is either
+  empty or the key of the root is between @blo@ and @bhi@.
+--------------------------------------------------------------------}
+trim :: Ord a => MaybeS a -> MaybeS a -> Set a -> Set a
+trim NothingS   NothingS   t = t
+trim (JustS lx) NothingS   t = greater lx t where greater lo (Bin _ x _ r) | x <= lo = greater lo r
+                                                  greater _  t' = t'
+trim NothingS   (JustS hx) t = lesser hx t  where lesser  hi (Bin _ x l _) | x >= hi = lesser  hi l
+                                                  lesser  _  t' = t'
+trim (JustS lx) (JustS hx) t = middle lx hx t  where middle lo hi (Bin _ x _ r) | x <= lo = middle lo hi r
+                                                     middle lo hi (Bin _ x l _) | x >= hi = middle lo hi l
+                                                     middle _  _  t' = t'
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE trim #-}
+#endif
+
+{--------------------------------------------------------------------
+  [filterGt b t] filter all values >[b] from tree [t]
+  [filterLt b t] filter all values <[b] from tree [t]
+--------------------------------------------------------------------}
+filterGt :: Ord a => MaybeS a -> Set a -> Set a
+filterGt NothingS t = t
+filterGt (JustS b) t = filter' b t
+  where filter' _   Tip = Tip
+        filter' b' (Bin _ x l r) =
+          case compare b' x of LT -> link x (filter' b' l) r
+                               EQ -> r
+                               GT -> filter' b' r
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE filterGt #-}
+#endif
+
+filterLt :: Ord a => MaybeS a -> Set a -> Set a
+filterLt NothingS t = t
+filterLt (JustS b) t = filter' b t
+  where filter' _   Tip = Tip
+        filter' b' (Bin _ x l r) =
+          case compare x b' of LT -> link x l (filter' b' r)
+                               EQ -> l
+                               GT -> filter' b' l
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE filterLt #-}
+#endif
+
+{--------------------------------------------------------------------
+  Split
+--------------------------------------------------------------------}
+-- | /O(log n)/. The expression (@'split' x set@) is a pair @(set1,set2)@
+-- where @set1@ comprises the elements of @set@ less than @x@ and @set2@
+-- comprises the elements of @set@ greater than @x@.
+split :: Ord a => a -> Set a -> (Set a,Set a)
+split x0 t0 = toPair $ go x0 t0
+  where
+    go _ Tip = (Tip :*: Tip)
+    go x (Bin _ y l r)
+      = case compare x y of
+          LT -> let (lt :*: gt) = go x l in (lt :*: link y gt r)
+          GT -> let (lt :*: gt) = go x r in (link y l lt :*: gt)
+          EQ -> (l :*: r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE split #-}
+#endif
+
+-- | /O(log n)/. Performs a 'split' but also returns whether the pivot
+-- element was found in the original set.
+splitMember :: Ord a => a -> Set a -> (Set a,Bool,Set a)
+splitMember _ Tip = (Tip, False, Tip)
+splitMember x (Bin _ y l r)
+   = case compare x y of
+       LT -> let (lt, found, gt) = splitMember x l
+                 gt' = link y gt r
+             in gt' `seq` (lt, found, gt')
+       GT -> let (lt, found, gt) = splitMember x r
+                 lt' = link y l lt
+             in lt' `seq` (lt', found, gt)
+       EQ -> (l, True, r)
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE splitMember #-}
+#endif
+
+{--------------------------------------------------------------------
+  Indexing
+--------------------------------------------------------------------}
+
+-- | /O(log n)/. Return the /index/ of an element, which is its zero-based
+-- index in the sorted sequence of elements. The index is a number from /0/ up
+-- to, but not including, the 'size' of the set. Calls 'error' when the element
+-- is not a 'member' of the set.
+--
+-- > findIndex 2 (fromList [5,3])    Error: element is not in the set
+-- > findIndex 3 (fromList [5,3]) == 0
+-- > findIndex 5 (fromList [5,3]) == 1
+-- > findIndex 6 (fromList [5,3])    Error: element is not in the set
+
+-- See Note: Type of local 'go' function
+findIndex :: Ord a => a -> Set a -> Int
+findIndex = go 0
+  where
+    go :: Ord a => Int -> a -> Set a -> Int
+    STRICT_1_OF_3(go)
+    STRICT_2_OF_3(go)
+    go _   _ Tip  = error "Set.findIndex: element is not in the set"
+    go idx x (Bin _ kx l r) = case compare x kx of
+      LT -> go idx x l
+      GT -> go (idx + size l + 1) x r
+      EQ -> idx + size l
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE findIndex #-}
+#endif
+
+-- | /O(log n)/. Lookup the /index/ of an element, which is its zero-based index in
+-- the sorted sequence of elements. The index is a number from /0/ up to, but not
+-- including, the 'size' of the set.
+--
+-- > isJust   (lookupIndex 2 (fromList [5,3])) == False
+-- > fromJust (lookupIndex 3 (fromList [5,3])) == 0
+-- > fromJust (lookupIndex 5 (fromList [5,3])) == 1
+-- > isJust   (lookupIndex 6 (fromList [5,3])) == False
+
+-- See Note: Type of local 'go' function
+lookupIndex :: Ord a => a -> Set a -> Maybe Int
+lookupIndex = go 0
+  where
+    go :: Ord a => Int -> a -> Set a -> Maybe Int
+    STRICT_1_OF_3(go)
+    STRICT_2_OF_3(go)
+    go _   _ Tip  = Nothing
+    go idx x (Bin _ kx l r) = case compare x kx of
+      LT -> go idx x l
+      GT -> go (idx + size l + 1) x r
+      EQ -> Just $! idx + size l
+#if __GLASGOW_HASKELL__ >= 700
+{-# INLINABLE lookupIndex #-}
+#endif
+
+-- | /O(log n)/. Retrieve an element by its /index/, i.e. by its zero-based
+-- index in the sorted sequence of elements. If the /index/ is out of range (less
+-- than zero, greater or equal to 'size' of the set), 'error' is called.
+--
+-- > elemAt 0 (fromList [5,3]) == 3
+-- > elemAt 1 (fromList [5,3]) == 5
+-- > elemAt 2 (fromList [5,3])    Error: index out of range
+
+elemAt :: Int -> Set a -> a
+STRICT_1_OF_2(elemAt)
+elemAt _ Tip = error "Set.elemAt: index out of range"
+elemAt i (Bin _ x l r)
+  = case compare i sizeL of
+      LT -> elemAt i l
+      GT -> elemAt (i-sizeL-1) r
+      EQ -> x
+  where
+    sizeL = size l
+
+-- | /O(log n)/. Delete the element at /index/, i.e. by its zero-based index in
+-- the sorted sequence of elements. If the /index/ is out of range (less than zero,
+-- greater or equal to 'size' of the set), 'error' is called.
+--
+-- > deleteAt 0    (fromList [5,3]) == singleton 5
+-- > deleteAt 1    (fromList [5,3]) == singleton 3
+-- > deleteAt 2    (fromList [5,3])    Error: index out of range
+-- > deleteAt (-1) (fromList [5,3])    Error: index out of range
+
+deleteAt :: Int -> Set a -> Set a
+deleteAt i t = i `seq`
+  case t of
+    Tip -> error "Set.deleteAt: index out of range"
+    Bin _ x l r -> case compare i sizeL of
+      LT -> balanceR x (deleteAt i l) r
+      GT -> balanceL x l (deleteAt (i-sizeL-1) r)
+      EQ -> glue l r
+      where
+        sizeL = size l
+
+
+{--------------------------------------------------------------------
+  Utility functions that maintain the balance properties of the tree.
+  All constructors assume that all values in [l] < [x] and all values
+  in [r] > [x], and that [l] and [r] are valid trees.
+
+  In order of sophistication:
+    [Bin sz x l r]    The type constructor.
+    [bin x l r]       Maintains the correct size, assumes that both [l]
+                      and [r] are balanced with respect to each other.
+    [balance x l r]   Restores the balance and size.
+                      Assumes that the original tree was balanced and
+                      that [l] or [r] has changed by at most one element.
+    [link x l r]      Restores balance and size.
+
+  Furthermore, we can construct a new tree from two trees. Both operations
+  assume that all values in [l] < all values in [r] and that [l] and [r]
+  are valid:
+    [glue l r]        Glues [l] and [r] together. Assumes that [l] and
+                      [r] are already balanced with respect to each other.
+    [merge l r]       Merges two trees and restores balance.
+
+  Note: in contrast to Adam's paper, we use (<=) comparisons instead
+  of (<) comparisons in [link], [merge] and [balance].
+  Quickcheck (on [difference]) showed that this was necessary in order
+  to maintain the invariants. It is quite unsatisfactory that I haven't
+  been able to find out why this is actually the case! Fortunately, it
+  doesn't hurt to be a bit more conservative.
+--------------------------------------------------------------------}
+
+{--------------------------------------------------------------------
+  Link
+--------------------------------------------------------------------}
+link :: a -> Set a -> Set a -> Set a
+link x Tip r  = insertMin x r
+link x l Tip  = insertMax x l
+link x l@(Bin sizeL y ly ry) r@(Bin sizeR z lz rz)
+  | delta*sizeL < sizeR  = balanceL z (link x l lz) rz
+  | delta*sizeR < sizeL  = balanceR y ly (link x ry r)
+  | otherwise            = bin x l r
+
+
+-- insertMin and insertMax don't perform potentially expensive comparisons.
+insertMax,insertMin :: a -> Set a -> Set a
+insertMax x t
+  = case t of
+      Tip -> singleton x
+      Bin _ y l r
+          -> balanceR y l (insertMax x r)
+
+insertMin x t
+  = case t of
+      Tip -> singleton x
+      Bin _ y l r
+          -> balanceL y (insertMin x l) r
+
+{--------------------------------------------------------------------
+  [merge l r]: merges two trees.
+--------------------------------------------------------------------}
+merge :: Set a -> Set a -> Set a
+merge Tip r   = r
+merge l Tip   = l
+merge l@(Bin sizeL x lx rx) r@(Bin sizeR y ly ry)
+  | delta*sizeL < sizeR = balanceL y (merge l ly) ry
+  | delta*sizeR < sizeL = balanceR x lx (merge rx r)
+  | otherwise           = glue l r
+
+{--------------------------------------------------------------------
+  [glue l r]: glues two trees together.
+  Assumes that [l] and [r] are already balanced with respect to each other.
+--------------------------------------------------------------------}
+glue :: Set a -> Set a -> Set a
+glue Tip r = r
+glue l Tip = l
+glue l r
+  | size l > size r = let (m,l') = deleteFindMax l in balanceR m l' r
+  | otherwise       = let (m,r') = deleteFindMin r in balanceL m l r'
+
+-- | /O(log n)/. Delete and find the minimal element.
+--
+-- > deleteFindMin set = (findMin set, deleteMin set)
+
+deleteFindMin :: Set a -> (a,Set a)
+deleteFindMin t
+  = case t of
+      Bin _ x Tip r -> (x,r)
+      Bin _ x l r   -> let (xm,l') = deleteFindMin l in (xm,balanceR x l' r)
+      Tip           -> (error "Set.deleteFindMin: can not return the minimal element of an empty set", Tip)
+
+-- | /O(log n)/. Delete and find the maximal element.
+--
+-- > deleteFindMax set = (findMax set, deleteMax set)
+deleteFindMax :: Set a -> (a,Set a)
+deleteFindMax t
+  = case t of
+      Bin _ x l Tip -> (x,l)
+      Bin _ x l r   -> let (xm,r') = deleteFindMax r in (xm,balanceL x l r')
+      Tip           -> (error "Set.deleteFindMax: can not return the maximal element of an empty set", Tip)
+
+-- | /O(log n)/. Retrieves the minimal key of the set, and the set
+-- stripped of that element, or 'Nothing' if passed an empty set.
+minView :: Set a -> Maybe (a, Set a)
+minView Tip = Nothing
+minView x = Just (deleteFindMin x)
+
+-- | /O(log n)/. Retrieves the maximal key of the set, and the set
+-- stripped of that element, or 'Nothing' if passed an empty set.
+maxView :: Set a -> Maybe (a, Set a)
+maxView Tip = Nothing
+maxView x = Just (deleteFindMax x)
+
+{--------------------------------------------------------------------
+  [balance x l r] balances two trees with value x.
+  The sizes of the trees should balance after decreasing the
+  size of one of them. (a rotation).
+
+  [delta] is the maximal relative difference between the sizes of
+          two trees, it corresponds with the [w] in Adams' paper.
+  [ratio] is the ratio between an outer and inner sibling of the
+          heavier subtree in an unbalanced setting. It determines
+          whether a double or single rotation should be performed
+          to restore balance. It is correspondes with the inverse
+          of $\alpha$ in Adam's article.
+
+  Note that according to the Adam's paper:
+  - [delta] should be larger than 4.646 with a [ratio] of 2.
+  - [delta] should be larger than 3.745 with a [ratio] of 1.534.
+
+  But the Adam's paper is errorneous:
+  - it can be proved that for delta=2 and delta>=5 there does
+    not exist any ratio that would work
+  - delta=4.5 and ratio=2 does not work
+
+  That leaves two reasonable variants, delta=3 and delta=4,
+  both with ratio=2.
+
+  - A lower [delta] leads to a more 'perfectly' balanced tree.
+  - A higher [delta] performs less rebalancing.
+
+  In the benchmarks, delta=3 is faster on insert operations,
+  and delta=4 has slightly better deletes. As the insert speedup
+  is larger, we currently use delta=3.
+
+--------------------------------------------------------------------}
+delta,ratio :: Int
+delta = 3
+ratio = 2
+
+-- The balance function is equivalent to the following:
+--
+--   balance :: a -> Set a -> Set a -> Set a
+--   balance x l r
+--     | sizeL + sizeR <= 1   = Bin sizeX x l r
+--     | sizeR > delta*sizeL  = rotateL x l r
+--     | sizeL > delta*sizeR  = rotateR x l r
+--     | otherwise            = Bin sizeX x l r
+--     where
+--       sizeL = size l
+--       sizeR = size r
+--       sizeX = sizeL + sizeR + 1
+--
+--   rotateL :: a -> Set a -> Set a -> Set a
+--   rotateL x l r@(Bin _ _ ly ry) | size ly < ratio*size ry = singleL x l r
+--                                 | otherwise               = doubleL x l r
+--   rotateR :: a -> Set a -> Set a -> Set a
+--   rotateR x l@(Bin _ _ ly ry) r | size ry < ratio*size ly = singleR x l r
+--                                 | otherwise               = doubleR x l r
+--
+--   singleL, singleR :: a -> Set a -> Set a -> Set a
+--   singleL x1 t1 (Bin _ x2 t2 t3)  = bin x2 (bin x1 t1 t2) t3
+--   singleR x1 (Bin _ x2 t1 t2) t3  = bin x2 t1 (bin x1 t2 t3)
+--
+--   doubleL, doubleR :: a -> Set a -> Set a -> Set a
+--   doubleL x1 t1 (Bin _ x2 (Bin _ x3 t2 t3) t4) = bin x3 (bin x1 t1 t2) (bin x2 t3 t4)
+--   doubleR x1 (Bin _ x2 t1 (Bin _ x3 t2 t3)) t4 = bin x3 (bin x2 t1 t2) (bin x1 t3 t4)
+--
+-- It is only written in such a way that every node is pattern-matched only once.
+--
+-- Only balanceL and balanceR are needed at the moment, so balance is not here anymore.
+-- In case it is needed, it can be found in Data.Map.
+
+-- Functions balanceL and balanceR are specialised versions of balance.
+-- balanceL only checks whether the left subtree is too big,
+-- balanceR only checks whether the right subtree is too big.
+
+-- balanceL is called when left subtree might have been inserted to or when
+-- right subtree might have been deleted from.
+balanceL :: a -> Set a -> Set a -> Set a
+balanceL x l r = case r of
+  Tip -> case l of
+           Tip -> Bin 1 x Tip Tip
+           (Bin _ _ Tip Tip) -> Bin 2 x l Tip
+           (Bin _ lx Tip (Bin _ lrx _ _)) -> Bin 3 lrx (Bin 1 lx Tip Tip) (Bin 1 x Tip Tip)
+           (Bin _ lx ll@(Bin _ _ _ _) Tip) -> Bin 3 lx ll (Bin 1 x Tip Tip)
+           (Bin ls lx ll@(Bin lls _ _ _) lr@(Bin lrs lrx lrl lrr))
+             | lrs < ratio*lls -> Bin (1+ls) lx ll (Bin (1+lrs) x lr Tip)
+             | otherwise -> Bin (1+ls) lrx (Bin (1+lls+size lrl) lx ll lrl) (Bin (1+size lrr) x lrr Tip)
+
+  (Bin rs _ _ _) -> case l of
+           Tip -> Bin (1+rs) x Tip r
+
+           (Bin ls lx ll lr)
+              | ls > delta*rs  -> case (ll, lr) of
+                   (Bin lls _ _ _, Bin lrs lrx lrl lrr)
+                     | lrs < ratio*lls -> Bin (1+ls+rs) lx ll (Bin (1+rs+lrs) x lr r)
+                     | otherwise -> Bin (1+ls+rs) lrx (Bin (1+lls+size lrl) lx ll lrl) (Bin (1+rs+size lrr) x lrr r)
+                   (_, _) -> error "Failure in Data.Map.balanceL"
+              | otherwise -> Bin (1+ls+rs) x l r
+{-# NOINLINE balanceL #-}
+
+-- balanceR is called when right subtree might have been inserted to or when
+-- left subtree might have been deleted from.
+balanceR :: a -> Set a -> Set a -> Set a
+balanceR x l r = case l of
+  Tip -> case r of
+           Tip -> Bin 1 x Tip Tip
+           (Bin _ _ Tip Tip) -> Bin 2 x Tip r
+           (Bin _ rx Tip rr@(Bin _ _ _ _)) -> Bin 3 rx (Bin 1 x Tip Tip) rr
+           (Bin _ rx (Bin _ rlx _ _) Tip) -> Bin 3 rlx (Bin 1 x Tip Tip) (Bin 1 rx Tip Tip)
+           (Bin rs rx rl@(Bin rls rlx rll rlr) rr@(Bin rrs _ _ _))
+             | rls < ratio*rrs -> Bin (1+rs) rx (Bin (1+rls) x Tip rl) rr
+             | otherwise -> Bin (1+rs) rlx (Bin (1+size rll) x Tip rll) (Bin (1+rrs+size rlr) rx rlr rr)
+
+  (Bin ls _ _ _) -> case r of
+           Tip -> Bin (1+ls) x l Tip
+
+           (Bin rs rx rl rr)
+              | rs > delta*ls  -> case (rl, rr) of
+                   (Bin rls rlx rll rlr, Bin rrs _ _ _)
+                     | rls < ratio*rrs -> Bin (1+ls+rs) rx (Bin (1+ls+rls) x l rl) rr
+                     | otherwise -> Bin (1+ls+rs) rlx (Bin (1+ls+size rll) x l rll) (Bin (1+rrs+size rlr) rx rlr rr)
+                   (_, _) -> error "Failure in Data.Map.balanceR"
+              | otherwise -> Bin (1+ls+rs) x l r
+{-# NOINLINE balanceR #-}
+
+{--------------------------------------------------------------------
+  The bin constructor maintains the size of the tree
+--------------------------------------------------------------------}
+bin :: a -> Set a -> Set a -> Set a
+bin x l r
+  = Bin (size l + size r + 1) x l r
+{-# INLINE bin #-}
+
+
+{--------------------------------------------------------------------
+  Utilities
+--------------------------------------------------------------------}
+foldlStrict :: (a -> b -> a) -> a -> [b] -> a
+foldlStrict f = go
+  where
+    go z []     = z
+    go z (x:xs) = let z' = f z x in z' `seq` go z' xs
+{-# INLINE foldlStrict #-}
+
+-- | /O(1)/.  Decompose a set into pieces based on the structure of the underlying
+-- tree.  This function is useful for consuming a set in parallel.
+--
+-- No guarantee is made as to the sizes of the pieces; an internal, but
+-- deterministic process determines this.  However, it is guaranteed that the pieces
+-- returned will be in ascending order (all elements in the first subset less than all
+-- elements in the second, and so on).
+--
+-- Examples:
+--
+-- > splitRoot (fromList [1..6]) ==
+-- >   [fromList [1,2,3],fromList [4],fromList [5,6]]
+--
+-- > splitRoot empty == []
+--
+--  Note that the current implementation does not return more than three subsets,
+--  but you should not depend on this behaviour because it can change in the
+--  future without notice.
+splitRoot :: Set a -> [Set a]
+splitRoot orig =
+  case orig of
+    Tip           -> []
+    Bin _ v l r -> [l, singleton v, r]
+{-# INLINE splitRoot #-}
+
+
+{--------------------------------------------------------------------
+  Debugging
+--------------------------------------------------------------------}
+-- | /O(n)/. Show the tree that implements the set. The tree is shown
+-- in a compressed, hanging format.
+showTree :: Show a => Set a -> String
+showTree s
+  = showTreeWith True False s
+
+
+{- | /O(n)/. The expression (@showTreeWith hang wide map@) shows
+ the tree that implements the set. If @hang@ is
+ @True@, a /hanging/ tree is shown otherwise a rotated tree is shown. If
+ @wide@ is 'True', an extra wide version is shown.
+
+> Set> putStrLn $ showTreeWith True False $ fromDistinctAscList [1..5]
+> 4
+> +--2
+> |  +--1
+> |  +--3
+> +--5
+>
+> Set> putStrLn $ showTreeWith True True $ fromDistinctAscList [1..5]
+> 4
+> |
+> +--2
+> |  |
+> |  +--1
+> |  |
+> |  +--3
+> |
+> +--5
+>
+> Set> putStrLn $ showTreeWith False True $ fromDistinctAscList [1..5]
+> +--5
+> |
+> 4
+> |
+> |  +--3
+> |  |
+> +--2
+>    |
+>    +--1
+
+-}
+showTreeWith :: Show a => Bool -> Bool -> Set a -> String
+showTreeWith hang wide t
+  | hang      = (showsTreeHang wide [] t) ""
+  | otherwise = (showsTree wide [] [] t) ""
+
+showsTree :: Show a => Bool -> [String] -> [String] -> Set a -> ShowS
+showsTree wide lbars rbars t
+  = case t of
+      Tip -> showsBars lbars . showString "|\n"
+      Bin _ x Tip Tip
+          -> showsBars lbars . shows x . showString "\n"
+      Bin _ x l r
+          -> showsTree wide (withBar rbars) (withEmpty rbars) r .
+             showWide wide rbars .
+             showsBars lbars . shows x . showString "\n" .
+             showWide wide lbars .
+             showsTree wide (withEmpty lbars) (withBar lbars) l
+
+showsTreeHang :: Show a => Bool -> [String] -> Set a -> ShowS
+showsTreeHang wide bars t
+  = case t of
+      Tip -> showsBars bars . showString "|\n"
+      Bin _ x Tip Tip
+          -> showsBars bars . shows x . showString "\n"
+      Bin _ x l r
+          -> showsBars bars . shows x . showString "\n" .
+             showWide wide bars .
+             showsTreeHang wide (withBar bars) l .
+             showWide wide bars .
+             showsTreeHang wide (withEmpty bars) r
+
+showWide :: Bool -> [String] -> String -> String
+showWide wide bars
+  | wide      = showString (concat (reverse bars)) . showString "|\n"
+  | otherwise = id
+
+showsBars :: [String] -> ShowS
+showsBars bars
+  = case bars of
+      [] -> id
+      _  -> showString (concat (reverse (tail bars))) . showString node
+
+node :: String
+node           = "+--"
+
+withBar, withEmpty :: [String] -> [String]
+withBar bars   = "|  ":bars
+withEmpty bars = "   ":bars
+
+{--------------------------------------------------------------------
+  Assertions
+--------------------------------------------------------------------}
+-- | /O(n)/. Test if the internal set structure is valid.
+valid :: Ord a => Set a -> Bool
+valid t
+  = balanced t && ordered t && validsize t
+
+ordered :: Ord a => Set a -> Bool
+ordered t
+  = bounded (const True) (const True) t
+  where
+    bounded lo hi t'
+      = case t' of
+          Tip         -> True
+          Bin _ x l r -> (lo x) && (hi x) && bounded lo (<x) l && bounded (>x) hi r
+
+balanced :: Set a -> Bool
+balanced t
+  = case t of
+      Tip         -> True
+      Bin _ _ l r -> (size l + size r <= 1 || (size l <= delta*size r && size r <= delta*size l)) &&
+                     balanced l && balanced r
+
+validsize :: Set a -> Bool
+validsize t
+  = (realsize t == Just (size t))
+  where
+    realsize t'
+      = case t' of
+          Tip          -> Just 0
+          Bin sz _ l r -> case (realsize l,realsize r) of
+                            (Just n,Just m)  | n+m+1 == sz  -> Just sz
+                            _                -> Nothing
diff --git a/Data/StrictPair.hs b/Data/StrictPair.hs
new file mode 100644
--- /dev/null
+++ b/Data/StrictPair.hs
@@ -0,0 +1,13 @@
+{-# LANGUAGE CPP #-}
+#if !defined(TESTING) && __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Trustworthy #-}
+#endif
+module Data.StrictPair (StrictPair(..), toPair) where
+
+-- | Same as regular Haskell pairs, but (x :*: _|_) = (_|_ :*: y) =
+-- _|_
+data StrictPair a b = !a :*: !b
+
+toPair :: StrictPair a b -> (a, b)
+toPair (x :*: y) = (x, y)
+{-# INLINE toPair #-}
diff --git a/Data/Tree.hs b/Data/Tree.hs
new file mode 100644
--- /dev/null
+++ b/Data/Tree.hs
@@ -0,0 +1,170 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__
+{-# LANGUAGE DeriveDataTypeable, StandaloneDeriving #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 703
+{-# LANGUAGE Safe #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Tree
+-- Copyright   :  (c) The University of Glasgow 2002
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
+--
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Multi-way trees (/aka/ rose trees) and forests.
+--
+-----------------------------------------------------------------------------
+
+module Data.Tree(
+    Tree(..), Forest,
+    -- * Two-dimensional drawing
+    drawTree, drawForest,
+    -- * Extraction
+    flatten, levels,
+    -- * Building trees
+    unfoldTree, unfoldForest,
+    unfoldTreeM, unfoldForestM,
+    unfoldTreeM_BF, unfoldForestM_BF,
+    ) where
+
+import Control.Applicative (Applicative(..), (<$>))
+import Control.Monad (liftM)
+import Data.Monoid (Monoid(..))
+import Data.Sequence (Seq, empty, singleton, (<|), (|>), fromList,
+            ViewL(..), ViewR(..), viewl, viewr)
+import Data.Foldable (Foldable(foldMap), toList)
+import Data.Traversable (Traversable(traverse))
+import Data.Typeable
+import Control.DeepSeq (NFData(rnf))
+
+#ifdef __GLASGOW_HASKELL__
+import Data.Data (Data)
+#endif
+
+-- | Multi-way trees, also known as /rose trees/.
+data Tree a = Node {
+        rootLabel :: a,         -- ^ label value
+        subForest :: Forest a   -- ^ zero or more child trees
+    }
+#ifdef __GLASGOW_HASKELL__
+  deriving (Eq, Read, Show, Data)
+#else
+  deriving (Eq, Read, Show)
+#endif
+type Forest a = [Tree a]
+
+#include "Typeable.h"
+INSTANCE_TYPEABLE1(Tree,treeTc,"Tree")
+
+instance Functor Tree where
+    fmap f (Node x ts) = Node (f x) (map (fmap f) ts)
+
+instance Applicative Tree where
+    pure x = Node x []
+    Node f tfs <*> tx@(Node x txs) =
+        Node (f x) (map (f <$>) txs ++ map (<*> tx) tfs)
+
+instance Monad Tree where
+    return x = Node x []
+    Node x ts >>= f = Node x' (ts' ++ map (>>= f) ts)
+      where Node x' ts' = f x
+
+instance Traversable Tree where
+    traverse f (Node x ts) = Node <$> f x <*> traverse (traverse f) ts
+
+instance Foldable Tree where
+    foldMap f (Node x ts) = f x `mappend` foldMap (foldMap f) ts
+
+instance NFData a => NFData (Tree a) where
+    rnf (Node x ts) = rnf x `seq` rnf ts
+
+-- | Neat 2-dimensional drawing of a tree.
+drawTree :: Tree String -> String
+drawTree  = unlines . draw
+
+-- | Neat 2-dimensional drawing of a forest.
+drawForest :: Forest String -> String
+drawForest  = unlines . map drawTree
+
+draw :: Tree String -> [String]
+draw (Node x ts0) = x : drawSubTrees ts0
+  where
+    drawSubTrees [] = []
+    drawSubTrees [t] =
+        "|" : shift "`- " "   " (draw t)
+    drawSubTrees (t:ts) =
+        "|" : shift "+- " "|  " (draw t) ++ drawSubTrees ts
+
+    shift first other = zipWith (++) (first : repeat other)
+
+-- | The elements of a tree in pre-order.
+flatten :: Tree a -> [a]
+flatten t = squish t []
+  where squish (Node x ts) xs = x:Prelude.foldr squish xs ts
+
+-- | Lists of nodes at each level of the tree.
+levels :: Tree a -> [[a]]
+levels t =
+    map (map rootLabel) $
+        takeWhile (not . null) $
+        iterate (concatMap subForest) [t]
+
+-- | Build a tree from a seed value
+unfoldTree :: (b -> (a, [b])) -> b -> Tree a
+unfoldTree f b = let (a, bs) = f b in Node a (unfoldForest f bs)
+
+-- | Build a forest from a list of seed values
+unfoldForest :: (b -> (a, [b])) -> [b] -> Forest a
+unfoldForest f = map (unfoldTree f)
+
+-- | Monadic tree builder, in depth-first order
+unfoldTreeM :: Monad m => (b -> m (a, [b])) -> b -> m (Tree a)
+unfoldTreeM f b = do
+    (a, bs) <- f b
+    ts <- unfoldForestM f bs
+    return (Node a ts)
+
+-- | Monadic forest builder, in depth-first order
+#ifndef __NHC__
+unfoldForestM :: Monad m => (b -> m (a, [b])) -> [b] -> m (Forest a)
+#endif
+unfoldForestM f = Prelude.mapM (unfoldTreeM f)
+
+-- | Monadic tree builder, in breadth-first order,
+-- using an algorithm adapted from
+-- /Breadth-First Numbering: Lessons from a Small Exercise in Algorithm Design/,
+-- by Chris Okasaki, /ICFP'00/.
+unfoldTreeM_BF :: Monad m => (b -> m (a, [b])) -> b -> m (Tree a)
+unfoldTreeM_BF f b = liftM getElement $ unfoldForestQ f (singleton b)
+  where
+    getElement xs = case viewl xs of
+        x :< _ -> x
+        EmptyL -> error "unfoldTreeM_BF"
+
+-- | Monadic forest builder, in breadth-first order,
+-- using an algorithm adapted from
+-- /Breadth-First Numbering: Lessons from a Small Exercise in Algorithm Design/,
+-- by Chris Okasaki, /ICFP'00/.
+unfoldForestM_BF :: Monad m => (b -> m (a, [b])) -> [b] -> m (Forest a)
+unfoldForestM_BF f = liftM toList . unfoldForestQ f . fromList
+
+-- takes a sequence (queue) of seeds
+-- produces a sequence (reversed queue) of trees of the same length
+unfoldForestQ :: Monad m => (b -> m (a, [b])) -> Seq b -> m (Seq (Tree a))
+unfoldForestQ f aQ = case viewl aQ of
+    EmptyL -> return empty
+    a :< aQ' -> do
+        (b, as) <- f a
+        tQ <- unfoldForestQ f (Prelude.foldl (|>) aQ' as)
+        let (tQ', ts) = splitOnto [] as tQ
+        return (Node b ts <| tQ')
+  where
+    splitOnto :: [a'] -> [b'] -> Seq a' -> (Seq a', [a'])
+    splitOnto as [] q = (q, as)
+    splitOnto as (_:bs) q = case viewr q of
+        q' :> a -> splitOnto (a:as) bs q'
+        EmptyR -> error "unfoldForestQ"
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,31 @@
+The Glasgow Haskell Compiler License
+
+Copyright 2004, The University Court of the University of Glasgow.
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+- Redistributions of source code must retain the above copyright notice,
+this list of conditions and the following disclaimer.
+
+- Redistributions in binary form must reproduce the above copyright notice,
+this list of conditions and the following disclaimer in the documentation
+and/or other materials provided with the distribution.
+
+- Neither name of the University nor the names of its contributors may be
+used to endorse or promote products derived from this software without
+specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY COURT OF THE UNIVERSITY OF
+GLASGOW AND THE CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+UNIVERSITY COURT OF THE UNIVERSITY OF GLASGOW OR THE CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+DAMAGE.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,6 @@
+module Main (main) where
+
+import Distribution.Simple
+
+main :: IO ()
+main = defaultMain
diff --git a/benchmarks/IntMap.hs b/benchmarks/IntMap.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/IntMap.hs
@@ -0,0 +1,97 @@
+{-# LANGUAGE BangPatterns #-}
+module Main where
+
+import Control.DeepSeq
+import Control.Exception (evaluate)
+import Control.Monad.Trans (liftIO)
+import Criterion.Config
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.IntMap as M
+import Data.Maybe (fromMaybe)
+import Prelude hiding (lookup)
+
+main = do
+    let m = M.fromAscList elems :: M.IntMap Int
+    defaultMainWith
+        defaultConfig
+        (liftIO . evaluate $ rnf [m])
+        [ bench "lookup" $ whnf (lookup keys) m
+        , bench "insert" $ whnf (ins elems) M.empty
+        , bench "insertWith empty" $ whnf (insWith elems) M.empty
+        , bench "insertWith update" $ whnf (insWith elems) m
+        , bench "insertWith' empty" $ whnf (insWith' elems) M.empty
+        , bench "insertWith' update" $ whnf (insWith' elems) m
+        , bench "insertWithKey empty" $ whnf (insWithKey elems) M.empty
+        , bench "insertWithKey update" $ whnf (insWithKey elems) m
+        , bench "insertWithKey' empty" $ whnf (insWithKey' elems) M.empty
+        , bench "insertWithKey' update" $ whnf (insWithKey' elems) m
+        , bench "insertLookupWithKey empty" $ whnf (insLookupWithKey elems) M.empty
+        , bench "insertLookupWithKey update" $ whnf (insLookupWithKey elems) m
+        , bench "map" $ whnf (M.map (+ 1)) m
+        , bench "mapWithKey" $ whnf (M.mapWithKey (+)) m
+        , bench "foldlWithKey" $ whnf (ins elems) m
+        , bench "foldlWithKey'" $ whnf (M.foldlWithKey' sum 0) m
+        , bench "foldrWithKey" $ whnf (M.foldrWithKey consPair []) m
+        , bench "delete" $ whnf (del keys) m
+        , bench "update" $ whnf (upd keys) m
+        , bench "updateLookupWithKey" $ whnf (upd' keys) m
+        , bench "alter"  $ whnf (alt keys) m
+        , bench "mapMaybe" $ whnf (M.mapMaybe maybeDel) m
+        , bench "mapMaybeWithKey" $ whnf (M.mapMaybeWithKey (const maybeDel)) m
+        , bench "fromList" $ whnf M.fromList elems
+        , bench "fromAscList" $ whnf M.fromAscList elems
+        , bench "fromDistinctAscList" $ whnf M.fromDistinctAscList elems
+        ]
+  where
+    elems = zip keys values
+    keys = [1..2^12]
+    values = [1..2^12]
+    sum k v1 v2 = k + v1 + v2
+    consPair k v xs = (k, v) : xs
+
+add3 :: Int -> Int -> Int -> Int
+add3 x y z = x + y + z
+{-# INLINE add3 #-}
+
+lookup :: [Int] -> M.IntMap Int -> Int
+lookup xs m = foldl' (\n k -> fromMaybe n (M.lookup k m)) 0 xs
+
+ins :: [(Int, Int)] -> M.IntMap Int -> M.IntMap Int
+ins xs m = foldl' (\m (k, v) -> M.insert k v m) m xs
+
+insWith :: [(Int, Int)] -> M.IntMap Int -> M.IntMap Int
+insWith xs m = foldl' (\m (k, v) -> M.insertWith (+) k v m) m xs
+
+insWithKey :: [(Int, Int)] -> M.IntMap Int -> M.IntMap Int
+insWithKey xs m = foldl' (\m (k, v) -> M.insertWithKey add3 k v m) m xs
+
+insWith' :: [(Int, Int)] -> M.IntMap Int -> M.IntMap Int
+insWith' xs m = foldl' (\m (k, v) -> M.insertWith' (+) k v m) m xs
+
+insWithKey' :: [(Int, Int)] -> M.IntMap Int -> M.IntMap Int
+insWithKey' xs m = foldl' (\m (k, v) -> M.insertWithKey' add3 k v m) m xs
+
+data PairS a b = PS !a !b
+
+insLookupWithKey :: [(Int, Int)] -> M.IntMap Int -> (Int, M.IntMap Int)
+insLookupWithKey xs m = let !(PS a b) = foldl' f (PS 0 m) xs in (a, b)
+  where
+    f (PS n m) (k, v) = let !(n', m') = M.insertLookupWithKey add3 k v m
+                        in PS (fromMaybe 0 n' + n) m'
+
+del :: [Int] -> M.IntMap Int -> M.IntMap Int
+del xs m = foldl' (\m k -> M.delete k m) m xs
+
+upd :: [Int] -> M.IntMap Int -> M.IntMap Int
+upd xs m = foldl' (\m k -> M.update Just k m) m xs
+
+upd' :: [Int] -> M.IntMap Int -> M.IntMap Int
+upd' xs m = foldl' (\m k -> snd $ M.updateLookupWithKey (\_ a -> Just a) k m) m xs
+
+alt :: [Int] -> M.IntMap Int -> M.IntMap Int
+alt xs m = foldl' (\m k -> M.alter id k m) m xs
+
+maybeDel :: Int -> Maybe Int
+maybeDel n | n `mod` 3 == 0 = Nothing
+           | otherwise      = Just n
diff --git a/benchmarks/IntSet.hs b/benchmarks/IntSet.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/IntSet.hs
@@ -0,0 +1,51 @@
+{-# LANGUAGE BangPatterns #-}
+
+module Main where
+
+import Control.DeepSeq
+import Control.Exception (evaluate)
+import Control.Monad.Trans (liftIO)
+import Criterion.Config
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.IntSet as S
+
+main = do
+    let s = S.fromAscList elems :: S.IntSet
+        s_even = S.fromAscList elems_even :: S.IntSet
+        s_odd = S.fromAscList elems_odd :: S.IntSet
+    defaultMainWith
+        defaultConfig
+        (liftIO . evaluate $ rnf [s, s_even, s_odd])
+        [ bench "member" $ whnf (member elems) s
+        , bench "insert" $ whnf (ins elems) S.empty
+        , bench "map" $ whnf (S.map (+ 1)) s
+        , bench "filter" $ whnf (S.filter ((== 0) . (`mod` 2))) s
+        , bench "partition" $ whnf (S.partition ((== 0) . (`mod` 2))) s
+        , bench "fold" $ whnf (S.fold (:) []) s
+        , bench "delete" $ whnf (del elems) s
+        , bench "findMin" $ whnf S.findMin s
+        , bench "findMax" $ whnf S.findMax s
+        , bench "deleteMin" $ whnf S.deleteMin s
+        , bench "deleteMax" $ whnf S.deleteMax s
+        , bench "unions" $ whnf S.unions [s_even, s_odd]
+        , bench "union" $ whnf (S.union s_even) s_odd
+        , bench "difference" $ whnf (S.difference s) s_even
+        , bench "intersection" $ whnf (S.intersection s) s_even
+        , bench "fromList" $ whnf S.fromList elems
+        , bench "fromAscList" $ whnf S.fromAscList elems
+        , bench "fromDistinctAscList" $ whnf S.fromDistinctAscList elems
+        ]
+  where
+    elems = [1..2^12]
+    elems_even = [2,4..2^12]
+    elems_odd = [1,3..2^12]
+
+member :: [Int] -> S.IntSet -> Int
+member xs s = foldl' (\n x -> if S.member x s then n + 1 else n) 0 xs
+
+ins :: [Int] -> S.IntSet -> S.IntSet
+ins xs s0 = foldl' (\s a -> S.insert a s) s0 xs
+
+del :: [Int] -> S.IntSet -> S.IntSet
+del xs s0 = foldl' (\s k -> S.delete k s) s0 xs
diff --git a/benchmarks/LookupGE/IntMap.hs b/benchmarks/LookupGE/IntMap.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/LookupGE/IntMap.hs
@@ -0,0 +1,51 @@
+{-# LANGUAGE BangPatterns #-}
+module Main where
+
+import Control.DeepSeq
+import Control.Exception (evaluate)
+import Control.Monad.Trans (liftIO)
+import Criterion.Config
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.IntMap as M
+import qualified LookupGE_IntMap as M
+import Data.Maybe (fromMaybe)
+import Prelude hiding (lookup)
+
+main :: IO ()
+main = do
+    defaultMainWith
+        defaultConfig
+        (liftIO . evaluate $ rnf [m_even, m_odd, m_large])
+        [b f | b <- benches, f <- funs1]
+  where
+    m_even = M.fromAscList elems_even :: M.IntMap Int
+    m_odd  = M.fromAscList elems_odd :: M.IntMap Int
+    m_large = M.fromAscList elems_large :: M.IntMap Int
+    bound = 2^12
+    elems_even  = zip evens evens
+    elems_odd   = zip odds odds
+    elems_large = zip large large
+    evens = [2,4..bound]
+    odds  = [1,3..bound]
+    large = [1,100..50*bound]
+    benches =
+          [ \(n,fun) -> bench (n++" present")  $ nf (fge fun evens) m_even
+          , \(n,fun) -> bench (n++" absent")   $ nf (fge fun evens) m_odd
+          , \(n,fun) -> bench (n++" far")      $ nf (fge fun odds)  m_large
+          , \(n,fun) -> bench (n++" !present") $ nf (fge2 fun evens) m_even
+          , \(n,fun) -> bench (n++" !absent")  $ nf (fge2 fun evens) m_odd
+          , \(n,fun) -> bench (n++" !far")     $ nf (fge2 fun odds)  m_large
+          ]
+    funs1 = [ ("GE split", M.lookupGE1)
+            , ("GE Craig", M.lookupGE2)
+            , ("GE Twan", M.lookupGE3)
+            , ("GE Milan", M.lookupGE4) ]
+
+fge :: (Int -> M.IntMap Int -> Maybe (Int,Int)) -> [Int] -> M.IntMap Int -> (Int,Int)
+fge fun xs m = foldl' (\n k -> fromMaybe n (fun k m)) (0,0) xs
+
+-- forcing values inside tuples!
+fge2 :: (Int -> M.IntMap Int -> Maybe (Int,Int)) -> [Int] -> M.IntMap Int -> (Int,Int)
+fge2 fun xs m = foldl' (\n@(!_, !_) k -> fromMaybe n (fun k m)) (0,0) xs
+
diff --git a/benchmarks/LookupGE/LookupGE_IntMap.hs b/benchmarks/LookupGE/LookupGE_IntMap.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/LookupGE/LookupGE_IntMap.hs
@@ -0,0 +1,97 @@
+{-# LANGUAGE CPP #-}
+module LookupGE_IntMap where
+
+import Prelude hiding (null)
+import Data.IntMap.Base
+#ifdef TESTING
+import Test.QuickCheck
+#endif
+
+lookupGE1 :: Key -> IntMap a -> Maybe (Key,a)
+lookupGE1 k m =
+    case splitLookup k m of
+        (_,Just v,_)  -> Just (k,v)
+        (_,Nothing,r) -> findMinMaybe r
+
+lookupGE2 :: Key -> IntMap a -> Maybe (Key,a)
+lookupGE2 k t = case t of
+    Bin _ m l r | m < 0 -> if k >= 0
+      then go l
+      else case go r of
+        Nothing -> Just $ findMin l
+        justx -> justx
+    _ -> go t
+  where
+    go (Bin p m l r)
+      | nomatch k p m = if k < p
+        then Just $ findMin l
+        else Nothing
+      | zero k m = case go l of
+        Nothing -> Just $ findMin r
+        justx -> justx
+      | otherwise = go r
+    go (Tip ky y)
+      | k > ky = Nothing
+      | otherwise = Just (ky, y)
+    go Nil = Nothing
+
+lookupGE3 :: Key -> IntMap a -> Maybe (Key,a)
+lookupGE3 k t = k `seq` case t of
+    Bin _ m l r | m < 0 -> if k >= 0
+      then go Nothing l
+      else go (Just (findMin l)) r
+    _ -> go Nothing t
+  where
+    go def (Bin p m l r)
+      | nomatch k p m = if k < p then Just $ findMin l else def
+      | zero k m  = go (Just $ findMin r) l
+      | otherwise = go def r
+    go def (Tip ky y)
+      | k > ky    = def
+      | otherwise = Just (ky, y)
+    go def Nil  = def
+
+lookupGE4 :: Key -> IntMap a -> Maybe (Key,a)
+lookupGE4 k t = k `seq` case t of
+    Bin _ m l r | m < 0 -> if k >= 0 then go Nil l
+                                     else go l r
+    _ -> go Nil t
+  where
+    go def (Bin p m l r)
+      | nomatch k p m = if k < p then fMin l else fMin def
+      | zero k m  = go r l
+      | otherwise = go def r
+    go def (Tip ky y)
+      | k > ky    = fMin def
+      | otherwise = Just (ky, y)
+    go def Nil  = fMin def
+
+    fMin :: IntMap a -> Maybe (Key, a)
+    fMin Nil = Nothing
+    fMin (Tip ky y) = Just (ky, y)
+    fMin (Bin _ _ l _) = fMin l
+
+-------------------------------------------------------------------------------
+-- Utilities
+-------------------------------------------------------------------------------
+
+-- | /O(log n)/. The minimal key of the map.
+findMinMaybe :: IntMap a -> Maybe (Key, a)
+findMinMaybe m
+  | null m = Nothing
+  | otherwise = Just (findMin m)
+
+#ifdef TESTING
+-------------------------------------------------------------------------------
+-- Properties:
+-------------------------------------------------------------------------------
+
+prop_lookupGE12 :: Int -> [Int] -> Bool
+prop_lookupGE12 x xs = case fromList $ zip xs xs of m -> lookupGE1 x m == lookupGE2 x m
+
+prop_lookupGE13 :: Int -> [Int] -> Bool
+prop_lookupGE13 x xs = case fromList $ zip xs xs of m -> lookupGE1 x m == lookupGE3 x m
+
+prop_lookupGE14 :: Int -> [Int] -> Bool
+prop_lookupGE14 x xs = case fromList $ zip xs xs of m -> lookupGE1 x m == lookupGE4 x m
+#endif
diff --git a/benchmarks/LookupGE/LookupGE_Map.hs b/benchmarks/LookupGE/LookupGE_Map.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/LookupGE/LookupGE_Map.hs
@@ -0,0 +1,78 @@
+{-# LANGUAGE BangPatterns, CPP #-}
+module LookupGE_Map where
+
+import Data.Map.Base
+#ifdef TESTING
+import Test.QuickCheck
+#endif
+
+lookupGE1 :: Ord k => k -> Map k a -> Maybe (k,a)
+lookupGE1 k m =
+    case splitLookup k m of
+        (_,Just v,_)  -> Just (k,v)
+        (_,Nothing,r) -> findMinMaybe r
+{-# INLINABLE lookupGE1 #-}
+
+lookupGE2 :: Ord k => k -> Map k a -> Maybe (k,a)
+lookupGE2 = go
+  where
+    go !_ Tip = Nothing
+    go !k (Bin _ kx x l r) =
+        case compare k kx of
+            LT -> case go k l of
+                    Nothing -> Just (kx,x)
+                    ret -> ret
+            GT -> go k r
+            EQ -> Just (kx,x)
+{-# INLINABLE lookupGE2 #-}
+
+lookupGE3 :: Ord k => k -> Map k a -> Maybe (k,a)
+lookupGE3 = go Nothing
+  where
+    go def !_ Tip = def
+    go def !k (Bin _ kx x l r) =
+        case compare k kx of
+            LT -> go (Just (kx,x)) k l
+            GT -> go def k r
+            EQ -> Just (kx,x)
+{-# INLINABLE lookupGE3 #-}
+
+lookupGE4 :: Ord k => k -> Map k a -> Maybe (k,a)
+lookupGE4 k = k `seq` goNothing
+  where
+    goNothing Tip = Nothing
+    goNothing (Bin _ kx x l r) = case compare k kx of
+                                   LT -> goJust kx x l
+                                   EQ -> Just (kx, x)
+                                   GT -> goNothing r
+
+    goJust ky y Tip = Just (ky, y)
+    goJust ky y (Bin _ kx x l r) = case compare k kx of
+                                     LT -> goJust kx x l
+                                     EQ -> Just (kx, x)
+                                     GT -> goJust ky y r
+{-# INLINABLE lookupGE4 #-}
+
+-------------------------------------------------------------------------------
+-- Utilities
+-------------------------------------------------------------------------------
+
+findMinMaybe :: Map k a -> Maybe (k,a)
+findMinMaybe (Bin _ kx x Tip _)  = Just (kx,x)
+findMinMaybe (Bin _ _  _ l _)    = findMinMaybe l
+findMinMaybe Tip                 = Nothing
+
+#ifdef TESTING
+-------------------------------------------------------------------------------
+-- Properties:
+-------------------------------------------------------------------------------
+
+prop_lookupGE12 :: Int -> [Int] -> Bool
+prop_lookupGE12 x xs = case fromList $ zip xs xs of m -> lookupGE1 x m == lookupGE2 x m
+
+prop_lookupGE13 :: Int -> [Int] -> Bool
+prop_lookupGE13 x xs = case fromList $ zip xs xs of m -> lookupGE1 x m == lookupGE3 x m
+
+prop_lookupGE14 :: Int -> [Int] -> Bool
+prop_lookupGE14 x xs = case fromList $ zip xs xs of m -> lookupGE1 x m == lookupGE4 x m
+#endif
diff --git a/benchmarks/LookupGE/Makefile b/benchmarks/LookupGE/Makefile
new file mode 100644
--- /dev/null
+++ b/benchmarks/LookupGE/Makefile
@@ -0,0 +1,3 @@
+TOP = ..
+
+include ../Makefile
diff --git a/benchmarks/LookupGE/Map.hs b/benchmarks/LookupGE/Map.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/LookupGE/Map.hs
@@ -0,0 +1,50 @@
+{-# LANGUAGE BangPatterns #-}
+module Main where
+
+import Control.DeepSeq
+import Control.Exception (evaluate)
+import Control.Monad.Trans (liftIO)
+import Criterion.Config
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.Map as M
+import qualified LookupGE_Map as M
+import Data.Maybe (fromMaybe)
+import Prelude hiding (lookup)
+
+main :: IO ()
+main = do
+    defaultMainWith
+        defaultConfig
+        (liftIO . evaluate $ rnf [m_even, m_odd, m_large])
+        [b f | b <- benches, f <- funs1]
+  where
+    m_even = M.fromAscList elems_even :: M.Map Int Int
+    m_odd  = M.fromAscList elems_odd :: M.Map Int Int
+    m_large = M.fromAscList elems_large :: M.Map Int Int
+    bound = 2^10
+    elems_even  = zip evens evens
+    elems_odd   = zip odds odds
+    elems_large = zip large large
+    evens = [2,4..bound]
+    odds  = [1,3..bound]
+    large = [1,100..50*bound]
+    benches =
+          [ \(n,fun) -> bench (n++" present")  $ nf (fge fun evens) m_even
+          , \(n,fun) -> bench (n++" absent")   $ nf (fge fun evens) m_odd
+          , \(n,fun) -> bench (n++" far")      $ nf (fge fun odds)  m_large
+          , \(n,fun) -> bench (n++" !present") $ nf (fge2 fun evens) m_even
+          , \(n,fun) -> bench (n++" !absent")  $ nf (fge2 fun evens) m_odd
+          , \(n,fun) -> bench (n++" !far")     $ nf (fge2 fun odds)  m_large
+          ]
+    funs1 = [ ("GE split", M.lookupGE1)
+            , ("GE caseof", M.lookupGE2)
+            , ("GE Twan", M.lookupGE3)
+            , ("GE Milan", M.lookupGE4) ]
+
+fge :: (Int -> M.Map Int Int -> Maybe (Int,Int)) -> [Int] -> M.Map Int Int -> (Int,Int)
+fge fun xs m = foldl' (\n k -> fromMaybe n (fun k m)) (0,0) xs
+
+-- forcing values inside tuples!
+fge2 :: (Int -> M.Map Int Int -> Maybe (Int,Int)) -> [Int] -> M.Map Int Int -> (Int,Int)
+fge2 fun xs m = foldl' (\n@(!_, !_) k -> fromMaybe n (fun k m)) (0,0) xs
diff --git a/benchmarks/Makefile b/benchmarks/Makefile
new file mode 100644
--- /dev/null
+++ b/benchmarks/Makefile
@@ -0,0 +1,16 @@
+all:
+
+bench-%: %.hs force
+	ghc -O2 -DTESTING $< -i../$(TOP) -o $@ -outputdir tmp -rtsopts
+
+bench-%.csv: bench-%
+	./bench-$* $(BENCHMARK) -v -u bench-$*.csv
+
+.PHONY: force clean veryclean
+force:
+
+clean:
+	rm -rf tmp $(patsubst %.hs, bench-%, $(wildcard *.hs))
+
+veryclean: clean
+	rm -rf *.csv
diff --git a/benchmarks/Map.hs b/benchmarks/Map.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/Map.hs
@@ -0,0 +1,131 @@
+{-# LANGUAGE BangPatterns #-}
+module Main where
+
+import Control.DeepSeq
+import Control.Exception (evaluate)
+import Control.Monad.Trans (liftIO)
+import Criterion.Config
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.Map as M
+import Data.Maybe (fromMaybe)
+import Prelude hiding (lookup)
+
+main = do
+    let m = M.fromAscList elems :: M.Map Int Int
+        m_even = M.fromAscList elems_even :: M.Map Int Int
+        m_odd = M.fromAscList elems_odd :: M.Map Int Int
+    defaultMainWith
+        defaultConfig
+        (liftIO . evaluate $ rnf [m, m_even, m_odd])
+        [ bench "lookup absent" $ whnf (lookup evens) m_odd
+        , bench "lookup present" $ whnf (lookup evens) m_even
+        , bench "insert absent" $ whnf (ins elems_even) m_odd
+        , bench "insert present" $ whnf (ins elems_even) m_even
+        , bench "insertWith absent" $ whnf (insWith elems_even) m_odd
+        , bench "insertWith present" $ whnf (insWith elems_even) m_even
+        , bench "insertWith' absent" $ whnf (insWith' elems_even) m_odd
+        , bench "insertWith' present" $ whnf (insWith' elems_even) m_even
+        , bench "insertWithKey absent" $ whnf (insWithKey elems_even) m_odd
+        , bench "insertWithKey present" $ whnf (insWithKey elems_even) m_even
+        , bench "insertWithKey' absent" $ whnf (insWithKey' elems_even) m_odd
+        , bench "insertWithKey' present" $ whnf (insWithKey' elems_even) m_even
+        , bench "insertLookupWithKey absent" $ whnf (insLookupWithKey elems_even) m_odd
+        , bench "insertLookupWithKey present" $ whnf (insLookupWithKey elems_even) m_even
+        , bench "insertLookupWithKey' absent" $ whnf (insLookupWithKey' elems_even) m_odd
+        , bench "insertLookupWithKey' present" $ whnf (insLookupWithKey' elems_even) m_even
+        , bench "map" $ whnf (M.map (+ 1)) m
+        , bench "mapWithKey" $ whnf (M.mapWithKey (+)) m
+        , bench "foldlWithKey" $ whnf (ins elems) m
+--         , bench "foldlWithKey'" $ whnf (M.foldlWithKey' sum 0) m
+        , bench "foldrWithKey" $ whnf (M.foldrWithKey consPair []) m
+        , bench "delete absent" $ whnf (del evens) m_odd
+        , bench "delete present" $ whnf (del evens) m
+        , bench "update absent" $ whnf (upd Just evens) m_odd
+        , bench "update present" $ whnf (upd Just evens) m_even
+        , bench "update delete" $ whnf (upd (const Nothing) evens) m
+        , bench "updateLookupWithKey absent" $ whnf (upd' Just evens) m_odd
+        , bench "updateLookupWithKey present" $ whnf (upd' Just evens) m_even
+        , bench "updateLookupWithKey delete" $ whnf (upd' (const Nothing) evens) m
+        , bench "alter absent"  $ whnf (alt id evens) m_odd
+        , bench "alter insert"  $ whnf (alt (const (Just 1)) evens) m_odd
+        , bench "alter update"  $ whnf (alt id evens) m_even
+        , bench "alter delete"  $ whnf (alt (const Nothing) evens) m
+        , bench "mapMaybe" $ whnf (M.mapMaybe maybeDel) m
+        , bench "mapMaybeWithKey" $ whnf (M.mapMaybeWithKey (const maybeDel)) m
+        , bench "lookupIndex" $ whnf (lookupIndex keys) m
+        , bench "union" $ whnf (M.union m_even) m_odd
+        , bench "difference" $ whnf (M.difference m) m_even
+        , bench "intersection" $ whnf (M.intersection m) m_even
+        , bench "split" $ whnf (M.split (bound `div` 2)) m
+        , bench "fromList" $ whnf M.fromList elems
+        , bench "fromList-desc" $ whnf M.fromList (reverse elems)
+        , bench "fromAscList" $ whnf M.fromAscList elems
+        , bench "fromDistinctAscList" $ whnf M.fromDistinctAscList elems
+        ]
+  where
+    bound = 2^12
+    elems = zip keys values
+    elems_even = zip evens evens
+    elems_odd = zip odds odds
+    keys = [1..bound]
+    evens = [2,4..bound]
+    odds = [1,3..bound]
+    values = [1..bound]
+    sum k v1 v2 = k + v1 + v2
+    consPair k v xs = (k, v) : xs
+
+add3 :: Int -> Int -> Int -> Int
+add3 x y z = x + y + z
+{-# INLINE add3 #-}
+
+lookup :: [Int] -> M.Map Int Int -> Int
+lookup xs m = foldl' (\n k -> fromMaybe n (M.lookup k m)) 0 xs
+
+lookupIndex :: [Int] -> M.Map Int Int -> Int
+lookupIndex xs m = foldl' (\n k -> fromMaybe n (M.lookupIndex k m)) 0 xs
+
+ins :: [(Int, Int)] -> M.Map Int Int -> M.Map Int Int
+ins xs m = foldl' (\m (k, v) -> M.insert k v m) m xs
+
+insWith :: [(Int, Int)] -> M.Map Int Int -> M.Map Int Int
+insWith xs m = foldl' (\m (k, v) -> M.insertWith (+) k v m) m xs
+
+insWithKey :: [(Int, Int)] -> M.Map Int Int -> M.Map Int Int
+insWithKey xs m = foldl' (\m (k, v) -> M.insertWithKey add3 k v m) m xs
+
+insWith' :: [(Int, Int)] -> M.Map Int Int -> M.Map Int Int
+insWith' xs m = foldl' (\m (k, v) -> M.insertWith' (+) k v m) m xs
+
+insWithKey' :: [(Int, Int)] -> M.Map Int Int -> M.Map Int Int
+insWithKey' xs m = foldl' (\m (k, v) -> M.insertWithKey' add3 k v m) m xs
+
+data PairS a b = PS !a !b
+
+insLookupWithKey :: [(Int, Int)] -> M.Map Int Int -> (Int, M.Map Int Int)
+insLookupWithKey xs m = let !(PS a b) = foldl' f (PS 0 m) xs in (a, b)
+  where
+    f (PS n m) (k, v) = let !(n', m') = M.insertLookupWithKey add3 k v m
+                        in PS (fromMaybe 0 n' + n) m'
+
+insLookupWithKey' :: [(Int, Int)] -> M.Map Int Int -> (Int, M.Map Int Int)
+insLookupWithKey' xs m = let !(PS a b) = foldl' f (PS 0 m) xs in (a, b)
+  where
+    f (PS n m) (k, v) = let !(n', m') = M.insertLookupWithKey' add3 k v m
+                        in PS (fromMaybe 0 n' + n) m'
+
+del :: [Int] -> M.Map Int Int -> M.Map Int Int
+del xs m = foldl' (\m k -> M.delete k m) m xs
+
+upd :: (Int -> Maybe Int) -> [Int] -> M.Map Int Int -> M.Map Int Int
+upd f xs m = foldl' (\m k -> M.update f k m) m xs
+
+upd' :: (Int -> Maybe Int) -> [Int] -> M.Map Int Int -> M.Map Int Int
+upd' f xs m = foldl' (\m k -> snd $ M.updateLookupWithKey (\_ a -> f a) k m) m xs
+
+alt :: (Maybe Int -> Maybe Int) -> [Int] -> M.Map Int Int -> M.Map Int Int
+alt f xs m = foldl' (\m k -> M.alter f k m) m xs
+
+maybeDel :: Int -> Maybe Int
+maybeDel n | n `mod` 3 == 0 = Nothing
+           | otherwise      = Just n
diff --git a/benchmarks/Sequence.hs b/benchmarks/Sequence.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/Sequence.hs
@@ -0,0 +1,34 @@
+-- > ghc -DTESTING --make -O2 -fforce-recomp -i.. Sequence.hs
+module Main where
+
+import Control.DeepSeq
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.Sequence as S
+import qualified Data.Foldable
+import System.Random
+
+main = do
+    let s10 = S.fromList [1..10] :: S.Seq Int
+        s100 = S.fromList [1..100] :: S.Seq Int
+        s1000 = S.fromList [1..1000] :: S.Seq Int
+    rnf [s10, s100, s1000] `seq` return ()
+    let g = mkStdGen 1
+    let rlist n = map (`mod` (n+1)) (take 10000 (randoms g)) :: [Int]
+        r10 = rlist 10
+        r100 = rlist 100
+        r1000 = rlist 1000
+    rnf [r10, r100, r1000] `seq` return ()
+    defaultMain
+        [ bench "splitAt/append 10" $ nf (shuffle r10) s10
+        , bench "splitAt/append 100" $ nf (shuffle r100) s100
+        , bench "splitAt/append 1000" $ nf (shuffle r1000) s1000
+        ]
+
+-- splitAt+append: repeatedly cut the sequence at a random point
+-- and rejoin the pieces in the opposite order.
+-- Finally getting the middle element forces the whole spine.
+shuffle :: [Int] -> S.Seq Int -> Int
+shuffle ps s = case S.viewl (S.drop (S.length s `div` 2) (foldl' cut s ps)) of
+    x S.:< _ -> x
+  where cut xs p = let (front, back) = S.splitAt p xs in back S.>< front
diff --git a/benchmarks/Set.hs b/benchmarks/Set.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/Set.hs
@@ -0,0 +1,53 @@
+{-# LANGUAGE BangPatterns #-}
+
+-- > ghc -DTESTING --make -O2 -fforce-recomp -i.. Set.hs
+module Main where
+
+import Control.DeepSeq
+import Control.Exception (evaluate)
+import Control.Monad.Trans (liftIO)
+import Criterion.Config
+import Criterion.Main
+import Data.List (foldl')
+import qualified Data.Set as S
+
+main = do
+    let s = S.fromAscList elems :: S.Set Int
+        s_even = S.fromAscList elems_even :: S.Set Int
+        s_odd = S.fromAscList elems_odd :: S.Set Int
+    defaultMainWith
+        defaultConfig
+        (liftIO . evaluate $ rnf [s, s_even, s_odd])
+        [ bench "member" $ whnf (member elems) s
+        , bench "insert" $ whnf (ins elems) S.empty
+        , bench "map" $ whnf (S.map (+ 1)) s
+        , bench "filter" $ whnf (S.filter ((== 0) . (`mod` 2))) s
+        , bench "partition" $ whnf (S.partition ((== 0) . (`mod` 2))) s
+        , bench "fold" $ whnf (S.fold (:) []) s
+        , bench "delete" $ whnf (del elems) s
+        , bench "findMin" $ whnf S.findMin s
+        , bench "findMax" $ whnf S.findMax s
+        , bench "deleteMin" $ whnf S.deleteMin s
+        , bench "deleteMax" $ whnf S.deleteMax s
+        , bench "unions" $ whnf S.unions [s_even, s_odd]
+        , bench "union" $ whnf (S.union s_even) s_odd
+        , bench "difference" $ whnf (S.difference s) s_even
+        , bench "intersection" $ whnf (S.intersection s) s_even
+        , bench "fromList" $ whnf S.fromList elems
+        , bench "fromList-desc" $ whnf S.fromList (reverse elems)
+        , bench "fromAscList" $ whnf S.fromAscList elems
+        , bench "fromDistinctAscList" $ whnf S.fromDistinctAscList elems
+        ]
+  where
+    elems = [1..2^12]
+    elems_even = [2,4..2^12]
+    elems_odd = [1,3..2^12]
+
+member :: [Int] -> S.Set Int -> Int
+member xs s = foldl' (\n x -> if S.member x s then n + 1 else n) 0 xs
+
+ins :: [Int] -> S.Set Int -> S.Set Int
+ins xs s0 = foldl' (\s a -> S.insert a s) s0 xs
+
+del :: [Int] -> S.Set Int -> S.Set Int
+del xs s0 = foldl' (\s k -> S.delete k s) s0 xs
diff --git a/benchmarks/SetOperations/Makefile b/benchmarks/SetOperations/Makefile
new file mode 100644
--- /dev/null
+++ b/benchmarks/SetOperations/Makefile
@@ -0,0 +1,3 @@
+TOP = ..
+
+include ../Makefile
diff --git a/benchmarks/SetOperations/SetOperations-IntMap.hs b/benchmarks/SetOperations/SetOperations-IntMap.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/SetOperations/SetOperations-IntMap.hs
@@ -0,0 +1,6 @@
+module Main where
+
+import Data.IntMap as C
+import SetOperations
+
+main = benchmark (\xs -> fromList [(x, x) | x <- xs]) True [("union", C.union), ("difference", C.difference), ("intersection", C.intersection)]
diff --git a/benchmarks/SetOperations/SetOperations-IntSet.hs b/benchmarks/SetOperations/SetOperations-IntSet.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/SetOperations/SetOperations-IntSet.hs
@@ -0,0 +1,6 @@
+module Main where
+
+import Data.IntSet as C
+import SetOperations
+
+main = benchmark fromList True [("union", C.union), ("difference", C.difference), ("intersection", C.intersection)]
diff --git a/benchmarks/SetOperations/SetOperations-Map.hs b/benchmarks/SetOperations/SetOperations-Map.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/SetOperations/SetOperations-Map.hs
@@ -0,0 +1,6 @@
+module Main where
+
+import Data.Map as C
+import SetOperations
+
+main = benchmark (\xs -> fromList [(x, x) | x <- xs]) True [("union", C.union), ("difference", C.difference), ("intersection", C.intersection)]
diff --git a/benchmarks/SetOperations/SetOperations-Set.hs b/benchmarks/SetOperations/SetOperations-Set.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/SetOperations/SetOperations-Set.hs
@@ -0,0 +1,6 @@
+module Main where
+
+import Data.Set as C
+import SetOperations
+
+main = benchmark fromList True [("union", C.union), ("difference", C.difference), ("intersection", C.intersection)]
diff --git a/benchmarks/SetOperations/SetOperations.hs b/benchmarks/SetOperations/SetOperations.hs
new file mode 100644
--- /dev/null
+++ b/benchmarks/SetOperations/SetOperations.hs
@@ -0,0 +1,45 @@
+{-# LANGUAGE BangPatterns #-}
+
+module SetOperations (benchmark) where
+
+import Criterion.Main
+import Data.List (partition)
+
+benchmark :: ([Int] -> container) -> Bool -> [(String, container -> container -> container)] -> IO ()
+benchmark fromList swap methods = do
+  defaultMain $ [ bench (method_str++"-"++input_str) $ whnf (method input1) input2 | (method_str, method) <- methods, (input_str, input1, input2) <- inputs ]
+
+  where
+    n, s, t :: Int
+    n = 100000
+    s {-small-} = n `div` 10
+    t {-tiny-} = round $ sqrt $ fromIntegral n
+
+    inputs = [ (mode_str, left, right)
+             | (mode_str, (left, right)) <- [ ("disj_nn", disj_nn), ("disj_ns", disj_ns), ("disj_nt", disj_nt)
+                                            , ("common_nn", common_nn), ("common_ns", common_ns), ("common_nt", common_nt)
+                                            , ("mix_nn", mix_nn), ("mix_ns", mix_ns), ("mix_nt", mix_nt)
+                                            , ("block_nn", block_nn), ("block_sn", block_ns)
+                                            ]
+
+             , (mode_str, left, right) <- replicate 2 (mode_str, left, right) ++
+                                          replicate (if swap && take 4 mode_str /= "diff" && last mode_str /= last (init mode_str) then 2 else 0)
+                                            (init (init mode_str) ++ [last mode_str] ++ [last (init mode_str)], right, left)
+             ]
+
+    all_n = fromList [1..n]
+
+    !disj_nn = seqPair $ (all_n, fromList [n+1..n+n])
+    !disj_ns = seqPair $ (all_n, fromList [n+1..n+s])
+    !disj_nt = seqPair $ (all_n, fromList [n+1..n+t])
+    !common_nn = seqPair $ (all_n, fromList [2,4..n])
+    !common_ns = seqPair $ (all_n, fromList [0,1+n`div`s..n])
+    !common_nt = seqPair $ (all_n, fromList [0,1+n`div`t..n])
+    !mix_nn = seqPair $ fromLists $ partition ((== 0) . (`mod` 2)) [1..n+n]
+    !mix_ns = seqPair $ fromLists $ partition ((== 0) . (`mod` (1 + n`div`s))) [1..s+n]
+    !mix_nt = seqPair $ fromLists $ partition ((== 0) . (`mod` (1 + n`div`t))) [1..t+n]
+    !block_nn = seqPair $ fromLists $ partition ((< t) . (`mod` (t * 2))) [1..n+n]
+    !block_ns = seqPair $ fromLists $ partition ((< t) . (`mod` (t * (1 + n`div`s)))) [1..s+n]
+
+    fromLists (xs, ys) = (fromList xs, fromList ys)
+    seqPair pair@(xs, ys) = xs `seq` ys `seq` pair
diff --git a/benchmarks/bench-cmp.pl b/benchmarks/bench-cmp.pl
new file mode 100644
--- /dev/null
+++ b/benchmarks/bench-cmp.pl
@@ -0,0 +1,24 @@
+#!/usr/bin/perl
+use warnings;
+use strict;
+
+@ARGV >= 2 or die "Usage: bench-cmp.pl csv_file_1 csv_file_2";
+open (my $f1, "<", $ARGV[0]) or die "Cannot open file $ARGV[0]";
+open (my $f2, "<", $ARGV[1]) or die "Cannot open file $ARGV[1]";
+
+my $l1 = <$f1>;
+my $l2 = <$f2>;
+$l1 eq $l2 or die "CSV files do not correspond -- $l1 and $l2";
+
+while (defined($l1 = <$f1>)) {
+  $l2 = <$f2>;
+
+  my @parts1 = split /,/, $l1;
+  my @parts2 = split /,/, $l2;
+
+  $parts1[0] eq $parts2[0] or die "CSV files do not correspond -- $parts1[0] and $parts2[0]";
+  printf "%s;%+7.2f%%;%.2e\n", $parts1[0], 100 * $parts2[1] / $parts1[1] - 100, $parts1[1];
+}
+
+close $f2;
+close $f1;
diff --git a/benchmarks/bench-cmp.sh b/benchmarks/bench-cmp.sh
new file mode 100644
--- /dev/null
+++ b/benchmarks/bench-cmp.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+./bench-cmp.pl "$@" | column -nts\; | less -SR
diff --git a/exposed-containers.cabal b/exposed-containers.cabal
new file mode 100644
--- /dev/null
+++ b/exposed-containers.cabal
@@ -0,0 +1,246 @@
+name: exposed-containers
+version: 0.5.5.1
+license: BSD3
+license-file: LICENSE
+maintainer: fox@ucw.cz
+bug-reports: https://github.com/haskell/containers/issues
+synopsis: A distribution of the 'containers' package, with all modules exposed.
+category: Data Structures
+description:
+    The source package contains efficient general-purpose implementations of
+    various basic immutable container types.  The declared cost of each
+    operation is either worst-case or amortized, but remains valid even if
+    structures are shared.
+
+    Here we redistribute it, but with hidden modules exposed.
+build-type: Simple
+cabal-version:  >=1.8
+extra-source-files:
+    include/Typeable.h
+    tests/Makefile
+    tests/*.hs
+    benchmarks/Makefile
+    benchmarks/bench-cmp.pl
+    benchmarks/bench-cmp.sh
+    benchmarks/*.hs
+    benchmarks/SetOperations/Makefile
+    benchmarks/SetOperations/*.hs
+    benchmarks/LookupGE/Makefile
+    benchmarks/LookupGE/*.hs
+
+source-repository head
+    type:     git
+    location: http://github.com/fmap/exposed-containers.git
+
+Library
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4
+    if impl(ghc>=6.10)
+        build-depends: ghc-prim
+
+    ghc-options: -O2 -Wall
+
+    exposed-modules:
+        Data.IntMap
+        Data.IntMap.Lazy
+        Data.IntMap.Strict
+        Data.IntSet
+        Data.Map
+        Data.Map.Lazy
+        Data.Map.Strict
+        Data.Set
+        Data.BitUtil
+        Data.IntMap.Base
+        Data.IntSet.Base
+        Data.Map.Base
+        Data.Set.Base
+        Data.StrictPair
+    if !impl(nhc98)
+        exposed-modules:
+            Data.Graph
+            Data.Sequence
+            Data.Tree
+
+    include-dirs: include
+
+    if impl(ghc<7.0)
+        extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+    if impl(ghc >= 7.8)
+        extensions: RoleAnnotations
+
+-------------------
+-- T E S T I N G --
+-------------------
+
+-- Every test-suite contains the build-depends and options of the library,
+-- plus the testing stuff.
+
+-- Because the test-suites cannot contain conditionals in GHC 7.0, the extensions
+-- are switched on for every compiler to allow GHC < 7.0 to compile the tests
+-- (because GHC < 7.0 cannot handle conditional LANGUAGE pragmas).
+-- When testing with GHC < 7.0 is not needed, the extensions should be removed.
+
+Test-suite map-lazy-properties
+    hs-source-dirs: tests, .
+    main-is: map-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        HUnit,
+        QuickCheck,
+        test-framework,
+        test-framework-hunit,
+        test-framework-quickcheck2
+
+Test-suite map-strict-properties
+    hs-source-dirs: tests, .
+    main-is: map-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING -DSTRICT
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        HUnit,
+        QuickCheck,
+        test-framework,
+        test-framework-hunit,
+        test-framework-quickcheck2
+
+Test-suite set-properties
+    hs-source-dirs: tests, .
+    main-is: set-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        HUnit,
+        QuickCheck,
+        test-framework,
+        test-framework-hunit,
+        test-framework-quickcheck2
+
+Test-suite intmap-lazy-properties
+    hs-source-dirs: tests, .
+    main-is: intmap-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        HUnit,
+        QuickCheck,
+        test-framework,
+        test-framework-hunit,
+        test-framework-quickcheck2
+
+Test-suite intmap-strict-properties
+    hs-source-dirs: tests, .
+    main-is: intmap-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING -DSTRICT
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        HUnit,
+        QuickCheck,
+        test-framework,
+        test-framework-hunit,
+        test-framework-quickcheck2
+
+Test-suite intset-properties
+    hs-source-dirs: tests, .
+    main-is: intset-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        HUnit,
+        QuickCheck,
+        test-framework,
+        test-framework-hunit,
+        test-framework-quickcheck2
+
+Test-suite deprecated-properties
+    hs-source-dirs: tests, .
+    main-is: deprecated-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        QuickCheck,
+        test-framework,
+        test-framework-quickcheck2
+
+Test-suite seq-properties
+    hs-source-dirs: tests, .
+    main-is: seq-properties.hs
+    type: exitcode-stdio-1.0
+    cpp-options: -DTESTING
+
+    build-depends: base >= 4.2 && < 5, array, deepseq >= 1.2 && < 1.4, ghc-prim
+    ghc-options: -O2
+    extensions: MagicHash, DeriveDataTypeable, StandaloneDeriving, Rank2Types
+
+    build-depends:
+        QuickCheck,
+        test-framework,
+        test-framework-quickcheck2
+
+test-suite map-strictness-properties
+  hs-source-dirs: tests, .
+  main-is: MapStrictness.hs
+  type: exitcode-stdio-1.0
+
+  build-depends:
+    array,
+    base >= 4.2 && < 5,
+    ChasingBottoms,
+    deepseq >= 1.2 && < 1.4,
+    QuickCheck >= 2.4.0.1,
+    ghc-prim,
+    test-framework >= 0.3.3,
+    test-framework-quickcheck2 >= 0.2.9
+
+  ghc-options: -Wall
+
+test-suite intmap-strictness-properties
+  hs-source-dirs: tests, .
+  main-is: IntMapStrictness.hs
+  type: exitcode-stdio-1.0
+
+  build-depends:
+    array,
+    base >= 4.2 && < 5,
+    ChasingBottoms,
+    deepseq >= 1.2 && < 1.4,
+    QuickCheck >= 2.4.0.1,
+    ghc-prim,
+    test-framework >= 0.3.3,
+    test-framework-quickcheck2 >= 0.2.9
+
+  ghc-options: -Wall
diff --git a/include/Typeable.h b/include/Typeable.h
new file mode 100644
--- /dev/null
+++ b/include/Typeable.h
@@ -0,0 +1,65 @@
+{- --------------------------------------------------------------------------
+// Macros to help make Typeable instances.
+//
+// INSTANCE_TYPEABLEn(tc,tcname,"tc") defines
+//
+//      instance Typeable/n/ tc
+//      instance Typeable a => Typeable/n-1/ (tc a)
+//      instance (Typeable a, Typeable b) => Typeable/n-2/ (tc a b)
+//      ...
+//      instance (Typeable a1, ..., Typeable an) => Typeable (tc a1 ... an)
+// --------------------------------------------------------------------------
+-}
+
+#ifndef TYPEABLE_H
+#define TYPEABLE_H
+
+#ifdef __GLASGOW_HASKELL__
+
+--  // For GHC, we can use DeriveDataTypeable + StandaloneDeriving to
+--  // generate the instances.
+
+#define INSTANCE_TYPEABLE0(tycon,tcname,str) deriving instance Typeable tycon
+#if __GLASGOW_HASKELL__ >= 707
+#define INSTANCE_TYPEABLE1(tycon,tcname,str) deriving instance Typeable tycon
+#define INSTANCE_TYPEABLE2(tycon,tcname,str) deriving instance Typeable tycon
+#define INSTANCE_TYPEABLE3(tycon,tcname,str) deriving instance Typeable tycon
+#else
+#define INSTANCE_TYPEABLE1(tycon,tcname,str) deriving instance Typeable1 tycon
+#define INSTANCE_TYPEABLE2(tycon,tcname,str) deriving instance Typeable2 tycon
+#define INSTANCE_TYPEABLE3(tycon,tcname,str) deriving instance Typeable3 tycon
+#endif
+
+#else /* !__GLASGOW_HASKELL__ */
+
+#define INSTANCE_TYPEABLE0(tycon,tcname,str) \
+tcname :: TyCon; \
+tcname = mkTyCon str; \
+instance Typeable tycon where { typeOf _ = mkTyConApp tcname [] }
+
+#define INSTANCE_TYPEABLE1(tycon,tcname,str) \
+tcname = mkTyCon str; \
+instance Typeable1 tycon where { typeOf1 _ = mkTyConApp tcname [] }; \
+instance Typeable a => Typeable (tycon a) where { typeOf = typeOfDefault }
+
+#define INSTANCE_TYPEABLE2(tycon,tcname,str) \
+tcname = mkTyCon str; \
+instance Typeable2 tycon where { typeOf2 _ = mkTyConApp tcname [] }; \
+instance Typeable a => Typeable1 (tycon a) where { \
+  typeOf1 = typeOf1Default }; \
+instance (Typeable a, Typeable b) => Typeable (tycon a b) where { \
+  typeOf = typeOfDefault }
+
+#define INSTANCE_TYPEABLE3(tycon,tcname,str) \
+tcname = mkTyCon str; \
+instance Typeable3 tycon where { typeOf3 _ = mkTyConApp tcname [] }; \
+instance Typeable a => Typeable2 (tycon a) where { \
+  typeOf2 = typeOf2Default }; \
+instance (Typeable a, Typeable b) => Typeable1 (tycon a b) where { \
+  typeOf1 = typeOf1Default }; \
+instance (Typeable a, Typeable b, Typeable c) => Typeable (tycon a b c) where { \
+  typeOf = typeOfDefault }
+
+#endif /* !__GLASGOW_HASKELL__ */
+
+#endif
diff --git a/tests/IntMapStrictness.hs b/tests/IntMapStrictness.hs
new file mode 100644
--- /dev/null
+++ b/tests/IntMapStrictness.hs
@@ -0,0 +1,127 @@
+{-# LANGUAGE FlexibleInstances, GeneralizedNewtypeDeriving #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Main (main) where
+
+import Test.ChasingBottoms.IsBottom
+import Test.Framework (Test, defaultMain, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+import Test.QuickCheck (Arbitrary(arbitrary))
+
+import Data.IntMap.Strict (IntMap)
+import qualified Data.IntMap.Strict as M
+
+instance Arbitrary v => Arbitrary (IntMap v) where
+    arbitrary = M.fromList `fmap` arbitrary
+
+instance Show (Int -> Int) where
+    show _ = "<function>"
+
+instance Show (Int -> Int -> Int) where
+    show _ = "<function>"
+
+instance Show (Int -> Int -> Int -> Int) where
+    show _ = "<function>"
+
+------------------------------------------------------------------------
+-- * Properties
+
+------------------------------------------------------------------------
+-- ** Strict module
+
+pSingletonKeyStrict :: Int -> Bool
+pSingletonKeyStrict v = isBottom $ M.singleton (bottom :: Int) v
+
+pSingletonValueStrict :: Int -> Bool
+pSingletonValueStrict k = isBottom $ (M.singleton k (bottom :: Int))
+
+pFindWithDefaultKeyStrict :: Int -> IntMap Int -> Bool
+pFindWithDefaultKeyStrict def m = isBottom $ M.findWithDefault def bottom m
+
+pFindWithDefaultValueStrict :: Int -> IntMap Int -> Bool
+pFindWithDefaultValueStrict k m =
+    M.member k m || (isBottom $ M.findWithDefault bottom k m)
+
+pAdjustKeyStrict :: (Int -> Int) -> IntMap Int -> Bool
+pAdjustKeyStrict f m = isBottom $ M.adjust f bottom m
+
+pAdjustValueStrict :: Int -> IntMap Int -> Bool
+pAdjustValueStrict k m
+    | k `M.member` m = isBottom $ M.adjust (const bottom) k m
+    | otherwise       = case M.keys m of
+        []     -> True
+        (k':_) -> isBottom $ M.adjust (const bottom) k' m
+
+pInsertKeyStrict :: Int -> IntMap Int -> Bool
+pInsertKeyStrict v m = isBottom $ M.insert bottom v m
+
+pInsertValueStrict :: Int -> IntMap Int -> Bool
+pInsertValueStrict k m = isBottom $ M.insert k bottom m
+
+pInsertWithKeyStrict :: (Int -> Int -> Int) -> Int -> IntMap Int -> Bool
+pInsertWithKeyStrict f v m = isBottom $ M.insertWith f bottom v m
+
+pInsertWithValueStrict :: (Int -> Int -> Int) -> Int -> Int -> IntMap Int
+                       -> Bool
+pInsertWithValueStrict f k v m
+    | M.member k m = (isBottom $ M.insertWith (const2 bottom) k v m) &&
+                     not (isBottom $ M.insertWith (const2 1) k bottom m)
+    | otherwise    = isBottom $ M.insertWith f k bottom m
+
+pInsertLookupWithKeyKeyStrict :: (Int -> Int -> Int -> Int) -> Int -> IntMap Int
+                              -> Bool
+pInsertLookupWithKeyKeyStrict f v m = isBottom $ M.insertLookupWithKey f bottom v m
+
+pInsertLookupWithKeyValueStrict :: (Int -> Int -> Int -> Int) -> Int -> Int
+                                -> IntMap Int -> Bool
+pInsertLookupWithKeyValueStrict f k v m
+    | M.member k m = (isBottom $ M.insertLookupWithKey (const3 bottom) k v m) &&
+                     not (isBottom $ M.insertLookupWithKey (const3 1) k bottom m)
+    | otherwise    = isBottom $ M.insertLookupWithKey f k bottom m
+
+------------------------------------------------------------------------
+-- * Test list
+
+tests :: [Test]
+tests =
+    [
+    -- Basic interface
+      testGroup "IntMap.Strict"
+      [ testProperty "singleton is key-strict" pSingletonKeyStrict
+      , testProperty "singleton is value-strict" pSingletonValueStrict
+      , testProperty "member is key-strict" $ keyStrict M.member
+      , testProperty "lookup is key-strict" $ keyStrict M.lookup
+      , testProperty "findWithDefault is key-strict" pFindWithDefaultKeyStrict
+      , testProperty "findWithDefault is value-strict" pFindWithDefaultValueStrict
+      , testProperty "! is key-strict" $ keyStrict (flip (M.!))
+      , testProperty "delete is key-strict" $ keyStrict M.delete
+      , testProperty "adjust is key-strict" pAdjustKeyStrict
+      , testProperty "adjust is value-strict" pAdjustValueStrict
+      , testProperty "insert is key-strict" pInsertKeyStrict
+      , testProperty "insert is value-strict" pInsertValueStrict
+      , testProperty "insertWith is key-strict" pInsertWithKeyStrict
+      , testProperty "insertWith is value-strict" pInsertWithValueStrict
+      , testProperty "insertLookupWithKey is key-strict"
+        pInsertLookupWithKeyKeyStrict
+      , testProperty "insertLookupWithKey is value-strict"
+        pInsertLookupWithKeyValueStrict
+      ]
+    ]
+
+------------------------------------------------------------------------
+-- * Test harness
+
+main :: IO ()
+main = defaultMain tests
+
+------------------------------------------------------------------------
+-- * Utilities
+
+keyStrict :: (Int -> IntMap Int -> a) -> IntMap Int -> Bool
+keyStrict f m = isBottom $ f bottom m
+
+const2 :: a -> b -> c -> a
+const2 x _ _ = x
+
+const3 :: a -> b -> c -> d -> a
+const3 x _ _ _ = x
diff --git a/tests/Makefile b/tests/Makefile
new file mode 100644
--- /dev/null
+++ b/tests/Makefile
@@ -0,0 +1,20 @@
+# The tests should be compiled and run using cabal:
+# > cabal configure --enable-tests
+# > cabal build
+# > cabal test
+#
+# This Makefile is used by developers to compile the tests manually.
+
+all:
+
+%-properties: %-properties.hs force
+	ghc -O2 -DTESTING $< -i.. -o $@ -outputdir tmp
+
+%-strict-properties: %-properties.hs force
+	ghc -O2 -DTESTING -DSTRICT $< -o $@ -i.. -outputdir tmp
+
+.PHONY: force clean
+force:
+
+clean:
+	rm -rf tmp $(patsubst %.hs, %, $(wildcard *-properties.hs)) $(patsubst %-properties.hs, %-strict-properties, $(wildcard *-properties.hs))
diff --git a/tests/MapStrictness.hs b/tests/MapStrictness.hs
new file mode 100644
--- /dev/null
+++ b/tests/MapStrictness.hs
@@ -0,0 +1,128 @@
+{-# LANGUAGE FlexibleInstances, GeneralizedNewtypeDeriving #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Main (main) where
+
+import Test.ChasingBottoms.IsBottom
+import Test.Framework (Test, defaultMain, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+import Test.QuickCheck (Arbitrary(arbitrary))
+
+import Data.Map.Strict (Map)
+import qualified Data.Map.Strict as M
+
+instance (Arbitrary k, Arbitrary v, Eq k, Ord k) =>
+         Arbitrary (Map k v) where
+    arbitrary = M.fromList `fmap` arbitrary
+
+instance Show (Int -> Int) where
+    show _ = "<function>"
+
+instance Show (Int -> Int -> Int) where
+    show _ = "<function>"
+
+instance Show (Int -> Int -> Int -> Int) where
+    show _ = "<function>"
+
+------------------------------------------------------------------------
+-- * Properties
+
+------------------------------------------------------------------------
+-- ** Strict module
+
+pSingletonKeyStrict :: Int -> Bool
+pSingletonKeyStrict v = isBottom $ M.singleton (bottom :: Int) v
+
+pSingletonValueStrict :: Int -> Bool
+pSingletonValueStrict k = isBottom $ (M.singleton k (bottom :: Int))
+
+pFindWithDefaultKeyStrict :: Int -> Map Int Int -> Bool
+pFindWithDefaultKeyStrict def m = isBottom $ M.findWithDefault def bottom m
+
+pFindWithDefaultValueStrict :: Int -> Map Int Int -> Bool
+pFindWithDefaultValueStrict k m =
+    M.member k m || (isBottom $ M.findWithDefault bottom k m)
+
+pAdjustKeyStrict :: (Int -> Int) -> Map Int Int -> Bool
+pAdjustKeyStrict f m = isBottom $ M.adjust f bottom m
+
+pAdjustValueStrict :: Int -> Map Int Int -> Bool
+pAdjustValueStrict k m
+    | k `M.member` m = isBottom $ M.adjust (const bottom) k m
+    | otherwise       = case M.keys m of
+        []     -> True
+        (k':_) -> isBottom $ M.adjust (const bottom) k' m
+
+pInsertKeyStrict :: Int -> Map Int Int -> Bool
+pInsertKeyStrict v m = isBottom $ M.insert bottom v m
+
+pInsertValueStrict :: Int -> Map Int Int -> Bool
+pInsertValueStrict k m = isBottom $ M.insert k bottom m
+
+pInsertWithKeyStrict :: (Int -> Int -> Int) -> Int -> Map Int Int -> Bool
+pInsertWithKeyStrict f v m = isBottom $ M.insertWith f bottom v m
+
+pInsertWithValueStrict :: (Int -> Int -> Int) -> Int -> Int -> Map Int Int
+                       -> Bool
+pInsertWithValueStrict f k v m
+    | M.member k m = (isBottom $ M.insertWith (const2 bottom) k v m) &&
+                     not (isBottom $ M.insertWith (const2 1) k bottom m)
+    | otherwise    = isBottom $ M.insertWith f k bottom m
+
+pInsertLookupWithKeyKeyStrict :: (Int -> Int -> Int -> Int) -> Int
+                              -> Map Int Int -> Bool
+pInsertLookupWithKeyKeyStrict f v m = isBottom $ M.insertLookupWithKey f bottom v m
+
+pInsertLookupWithKeyValueStrict :: (Int -> Int -> Int -> Int) -> Int -> Int
+                                -> Map Int Int -> Bool
+pInsertLookupWithKeyValueStrict f k v m
+    | M.member k m = (isBottom $ M.insertLookupWithKey (const3 bottom) k v m) &&
+                     not (isBottom $ M.insertLookupWithKey (const3 1) k bottom m)
+    | otherwise    = isBottom $ M.insertLookupWithKey f k bottom m
+
+------------------------------------------------------------------------
+-- * Test list
+
+tests :: [Test]
+tests =
+    [
+    -- Basic interface
+      testGroup "Map.Strict"
+      [ testProperty "singleton is key-strict" pSingletonKeyStrict
+      , testProperty "singleton is value-strict" pSingletonValueStrict
+      , testProperty "member is key-strict" $ keyStrict M.member
+      , testProperty "lookup is key-strict" $ keyStrict M.lookup
+      , testProperty "findWithDefault is key-strict" pFindWithDefaultKeyStrict
+      , testProperty "findWithDefault is value-strict" pFindWithDefaultValueStrict
+      , testProperty "! is key-strict" $ keyStrict (flip (M.!))
+      , testProperty "delete is key-strict" $ keyStrict M.delete
+      , testProperty "adjust is key-strict" pAdjustKeyStrict
+      , testProperty "adjust is value-strict" pAdjustValueStrict
+      , testProperty "insert is key-strict" pInsertKeyStrict
+      , testProperty "insert is value-strict" pInsertValueStrict
+      , testProperty "insertWith is key-strict" pInsertWithKeyStrict
+      , testProperty "insertWith is value-strict" pInsertWithValueStrict
+      , testProperty "insertLookupWithKey is key-strict"
+        pInsertLookupWithKeyKeyStrict
+      , testProperty "insertLookupWithKey is value-strict"
+        pInsertLookupWithKeyValueStrict
+      ]
+    ]
+
+------------------------------------------------------------------------
+-- * Test harness
+
+main :: IO ()
+main = defaultMain tests
+
+------------------------------------------------------------------------
+-- * Utilities
+
+keyStrict :: (Int -> Map Int Int -> a) -> Map Int Int -> Bool
+keyStrict f m = isBottom $ f bottom m
+
+const2 :: a -> b -> c -> a
+const2 x _ _ = x
+
+const3 :: a -> b -> c -> d -> a
+const3 x _ _ _ = x
diff --git a/tests/deprecated-properties.hs b/tests/deprecated-properties.hs
new file mode 100644
--- /dev/null
+++ b/tests/deprecated-properties.hs
@@ -0,0 +1,102 @@
+{-# LANGUAGE CPP #-}
+
+-- This module tests the deprecated properties of Data.Map and Data.IntMap,
+-- because these cannot be tested in either map-properties or
+-- intmap-properties, as these modules are designed to work with the .Lazy and
+-- .Strict modules.
+
+import qualified Data.Map as M
+import qualified Data.Map.Strict as SM
+import qualified Data.IntMap as IM
+import qualified Data.IntMap.Strict as SIM
+
+import Test.Framework
+import Test.Framework.Providers.QuickCheck2
+import Text.Show.Functions ()
+
+default (Int)
+
+main :: IO ()
+main = defaultMain
+         [ testProperty "Data.Map.insertWith' as Strict.insertWith" prop_mapInsertWith'Strict
+         , testProperty "Data.Map.insertWith' undefined value" prop_mapInsertWith'Undefined
+         , testProperty "Data.Map.insertWithKey' as Strict.insertWithKey" prop_mapInsertWithKey'Strict
+         , testProperty "Data.Map.insertWithKey' undefined value" prop_mapInsertWithKey'Undefined
+         , testProperty "Data.Map.insertLookupWithKey' as Strict.insertLookupWithKey" prop_mapInsertLookupWithKey'Strict
+         , testProperty "Data.Map.insertLookupWithKey' undefined value" prop_mapInsertLookupWithKey'Undefined
+         , testProperty "Data.IntMap.insertWith' as Strict.insertWith" prop_intmapInsertWith'Strict
+         , testProperty "Data.IntMap.insertWith' undefined value" prop_intmapInsertWith'Undefined
+         , testProperty "Data.IntMap.insertWithKey' as Strict.insertWithKey" prop_intmapInsertWithKey'Strict
+         , testProperty "Data.IntMap.insertWithKey' undefined value" prop_intmapInsertWithKey'Undefined
+         ]
+
+
+---------- Map properties ----------
+
+prop_mapInsertWith'Strict :: [(Int, Int)] -> (Int -> Int -> Int) -> [(Int, Int)] -> Bool
+prop_mapInsertWith'Strict xs f kxxs =
+  let m = M.fromList xs
+      insertList ins = foldr (\(kx, x) -> ins f kx x) m kxxs
+  in insertList M.insertWith' == insertList SM.insertWith
+
+prop_mapInsertWith'Undefined :: [(Int, Int)] -> Bool
+prop_mapInsertWith'Undefined xs =
+  let m = M.fromList xs
+      f _ x = x * 33
+      insertList ins = foldr (\(kx, _) -> ins f kx undefined) m xs
+  in insertList M.insertWith' == insertList M.insertWith
+
+prop_mapInsertWithKey'Strict :: [(Int, Int)] -> (Int -> Int -> Int -> Int) -> [(Int, Int)] -> Bool
+prop_mapInsertWithKey'Strict xs f kxxs =
+  let m = M.fromList xs
+      insertList ins = foldr (\(kx, x) -> ins f kx x) m kxxs
+  in insertList M.insertWithKey' == insertList SM.insertWithKey
+
+prop_mapInsertWithKey'Undefined :: [(Int, Int)] -> Bool
+prop_mapInsertWithKey'Undefined xs =
+  let m = M.fromList xs
+      f k _ x = (k + x) * 33
+      insertList ins = foldr (\(kx, _) -> ins f kx undefined) m xs
+  in insertList M.insertWithKey' == insertList M.insertWithKey
+
+prop_mapInsertLookupWithKey'Strict :: [(Int, Int)] -> (Int -> Int -> Int -> Int) -> [(Int, Int)] -> Bool
+prop_mapInsertLookupWithKey'Strict xs f kxxs =
+  let m = M.fromList xs
+      insertLookupList insLkp = scanr (\(kx, x) (_, mp) -> insLkp f kx x mp) (Nothing, m) kxxs
+  in insertLookupList M.insertLookupWithKey' == insertLookupList SM.insertLookupWithKey
+
+prop_mapInsertLookupWithKey'Undefined :: [(Int, Int)] -> Bool
+prop_mapInsertLookupWithKey'Undefined xs =
+  let m = M.fromList xs
+      f k _ x = (k + x) * 33
+      insertLookupList insLkp = scanr (\(kx, _) (_, mp) -> insLkp f kx undefined mp) (Nothing, m) xs
+  in insertLookupList M.insertLookupWithKey' == insertLookupList M.insertLookupWithKey
+
+
+---------- IntMap properties ----------
+
+prop_intmapInsertWith'Strict :: [(Int, Int)] -> (Int -> Int -> Int) -> [(Int, Int)] -> Bool
+prop_intmapInsertWith'Strict xs f kxxs =
+  let m = IM.fromList xs
+      insertList ins = foldr (\(kx, x) -> ins f kx x) m kxxs
+  in insertList IM.insertWith' == insertList SIM.insertWith
+
+prop_intmapInsertWith'Undefined :: [(Int, Int)] -> Bool
+prop_intmapInsertWith'Undefined xs =
+  let m = IM.fromList xs
+      f _ x = x * 33
+      insertList ins = foldr (\(kx, _) -> ins f kx undefined) m xs
+  in insertList IM.insertWith' == insertList IM.insertWith
+
+prop_intmapInsertWithKey'Strict :: [(Int, Int)] -> (Int -> Int -> Int -> Int) -> [(Int, Int)] -> Bool
+prop_intmapInsertWithKey'Strict xs f kxxs =
+  let m = IM.fromList xs
+      insertList ins = foldr (\(kx, x) -> ins f kx x) m kxxs
+  in insertList IM.insertWithKey' == insertList SIM.insertWithKey
+
+prop_intmapInsertWithKey'Undefined :: [(Int, Int)] -> Bool
+prop_intmapInsertWithKey'Undefined xs =
+  let m = IM.fromList xs
+      f k _ x = (k + x) * 33
+      insertList ins = foldr (\(kx, _) -> ins f kx undefined) m xs
+  in insertList IM.insertWithKey' == insertList IM.insertWithKey
diff --git a/tests/intmap-properties.hs b/tests/intmap-properties.hs
new file mode 100644
--- /dev/null
+++ b/tests/intmap-properties.hs
@@ -0,0 +1,1056 @@
+{-# LANGUAGE CPP #-}
+
+#ifdef STRICT
+import Data.IntMap.Strict as Data.IntMap
+#else
+import Data.IntMap.Lazy as Data.IntMap
+#endif
+
+import Data.Monoid
+import Data.Maybe hiding (mapMaybe)
+import qualified Data.Maybe as Maybe (mapMaybe)
+import Data.Ord
+import Data.Function
+import Prelude hiding (lookup, null, map, filter, foldr, foldl)
+import qualified Prelude (map)
+
+import Data.List (nub,sort)
+import qualified Data.List as List
+import qualified Data.IntSet
+import Test.Framework
+import Test.Framework.Providers.HUnit
+import Test.Framework.Providers.QuickCheck2
+import Test.HUnit hiding (Test, Testable)
+import Test.QuickCheck
+import Text.Show.Functions ()
+
+default (Int)
+
+main :: IO ()
+main = defaultMain
+         [
+               testCase "index"      test_index
+             , testCase "size"       test_size
+             , testCase "size2"      test_size2
+             , testCase "member"     test_member
+             , testCase "notMember"  test_notMember
+             , testCase "lookup"     test_lookup
+             , testCase "findWithDefault"     test_findWithDefault
+             , testCase "lookupLT"   test_lookupLT
+             , testCase "lookupGT"   test_lookupGT
+             , testCase "lookupLE"   test_lookupLE
+             , testCase "lookupGE"   test_lookupGE
+             , testCase "empty" test_empty
+             , testCase "mempty" test_mempty
+             , testCase "singleton" test_singleton
+             , testCase "insert" test_insert
+             , testCase "insertWith" test_insertWith
+             , testCase "insertWithKey" test_insertWithKey
+             , testCase "insertLookupWithKey" test_insertLookupWithKey
+             , testCase "delete" test_delete
+             , testCase "adjust" test_adjust
+             , testCase "adjustWithKey" test_adjustWithKey
+             , testCase "update" test_update
+             , testCase "updateWithKey" test_updateWithKey
+             , testCase "updateLookupWithKey" test_updateLookupWithKey
+             , testCase "alter" test_alter
+             , testCase "union" test_union
+             , testCase "mappend" test_mappend
+             , testCase "unionWith" test_unionWith
+             , testCase "unionWithKey" test_unionWithKey
+             , testCase "unions" test_unions
+             , testCase "mconcat" test_mconcat
+             , testCase "unionsWith" test_unionsWith
+             , testCase "difference" test_difference
+             , testCase "differenceWith" test_differenceWith
+             , testCase "differenceWithKey" test_differenceWithKey
+             , testCase "intersection" test_intersection
+             , testCase "intersectionWith" test_intersectionWith
+             , testCase "intersectionWithKey" test_intersectionWithKey
+             , testCase "map" test_map
+             , testCase "mapWithKey" test_mapWithKey
+             , testCase "mapAccum" test_mapAccum
+             , testCase "mapAccumWithKey" test_mapAccumWithKey
+             , testCase "mapAccumRWithKey" test_mapAccumRWithKey
+             , testCase "mapKeys" test_mapKeys
+             , testCase "mapKeysWith" test_mapKeysWith
+             , testCase "mapKeysMonotonic" test_mapKeysMonotonic
+             , testCase "elems" test_elems
+             , testCase "keys" test_keys
+             , testCase "assocs" test_assocs
+             , testCase "keysSet" test_keysSet
+             , testCase "keysSet" test_fromSet
+             , testCase "toList" test_toList
+             , testCase "fromList" test_fromList
+             , testCase "fromListWith" test_fromListWith
+             , testCase "fromListWithKey" test_fromListWithKey
+             , testCase "toAscList" test_toAscList
+             , testCase "toDescList" test_toDescList
+             , testCase "showTree" test_showTree
+             , testCase "fromAscList" test_fromAscList
+             , testCase "fromAscListWith" test_fromAscListWith
+             , testCase "fromAscListWithKey" test_fromAscListWithKey
+             , testCase "fromDistinctAscList" test_fromDistinctAscList
+             , testCase "filter" test_filter
+             , testCase "filterWithKey" test_filteWithKey
+             , testCase "partition" test_partition
+             , testCase "partitionWithKey" test_partitionWithKey
+             , testCase "mapMaybe" test_mapMaybe
+             , testCase "mapMaybeWithKey" test_mapMaybeWithKey
+             , testCase "mapEither" test_mapEither
+             , testCase "mapEitherWithKey" test_mapEitherWithKey
+             , testCase "split" test_split
+             , testCase "splitLookup" test_splitLookup
+             , testCase "isSubmapOfBy" test_isSubmapOfBy
+             , testCase "isSubmapOf" test_isSubmapOf
+             , testCase "isProperSubmapOfBy" test_isProperSubmapOfBy
+             , testCase "isProperSubmapOf" test_isProperSubmapOf
+             , testCase "findMin" test_findMin
+             , testCase "findMax" test_findMax
+             , testCase "deleteMin" test_deleteMin
+             , testCase "deleteMax" test_deleteMax
+             , testCase "deleteFindMin" test_deleteFindMin
+             , testCase "deleteFindMax" test_deleteFindMax
+             , testCase "updateMin" test_updateMin
+             , testCase "updateMax" test_updateMax
+             , testCase "updateMinWithKey" test_updateMinWithKey
+             , testCase "updateMaxWithKey" test_updateMaxWithKey
+             , testCase "minView" test_minView
+             , testCase "maxView" test_maxView
+             , testCase "minViewWithKey" test_minViewWithKey
+             , testCase "maxViewWithKey" test_maxViewWithKey
+             , testProperty "insert to singleton"  prop_singleton
+             , testProperty "insert then lookup"   prop_insertLookup
+             , testProperty "insert then delete"   prop_insertDelete
+             , testProperty "delete non member"    prop_deleteNonMember
+             , testProperty "union model"          prop_unionModel
+             , testProperty "union singleton"      prop_unionSingleton
+             , testProperty "union associative"    prop_unionAssoc
+             , testProperty "union+unionWith"      prop_unionWith
+             , testProperty "union sum"            prop_unionSum
+             , testProperty "difference model"     prop_differenceModel
+             , testProperty "intersection model"   prop_intersectionModel
+             , testProperty "intersectionWith model" prop_intersectionWithModel
+             , testProperty "intersectionWithKey model" prop_intersectionWithKeyModel
+             , testProperty "mergeWithKey model"   prop_mergeWithKeyModel
+             , testProperty "fromAscList"          prop_ordered
+             , testProperty "fromList then toList" prop_list
+             , testProperty "toDescList"           prop_descList
+             , testProperty "toAscList+toDescList" prop_ascDescList
+             , testProperty "fromList"             prop_fromList
+             , testProperty "alter"                prop_alter
+             , testProperty "index"                prop_index
+             , testProperty "null"                 prop_null
+             , testProperty "member"               prop_member
+             , testProperty "notmember"            prop_notmember
+             , testProperty "lookup"               prop_lookup
+             , testProperty "find"                 prop_find
+             , testProperty "findWithDefault"      prop_findWithDefault
+             , testProperty "lookupLT"             prop_lookupLT
+             , testProperty "lookupGT"             prop_lookupGT
+             , testProperty "lookupLE"             prop_lookupLE
+             , testProperty "lookupGE"             prop_lookupGE
+             , testProperty "findMin"              prop_findMin
+             , testProperty "findMax"              prop_findMax
+             , testProperty "deleteMin"            prop_deleteMinModel
+             , testProperty "deleteMax"            prop_deleteMaxModel
+             , testProperty "filter"               prop_filter
+             , testProperty "partition"            prop_partition
+             , testProperty "map"                  prop_map
+             , testProperty "fmap"                 prop_fmap
+             , testProperty "mapkeys"              prop_mapkeys
+             , testProperty "split"                prop_splitModel
+             , testProperty "splitRoot"            prop_splitRoot
+             , testProperty "foldr"                prop_foldr
+             , testProperty "foldr'"               prop_foldr'
+             , testProperty "foldl"                prop_foldl
+             , testProperty "foldl'"               prop_foldl'
+             , testProperty "keysSet"              prop_keysSet
+             , testProperty "fromSet"              prop_fromSet
+             ]
+
+{--------------------------------------------------------------------
+  Arbitrary, reasonably balanced trees
+--------------------------------------------------------------------}
+
+instance Arbitrary a => Arbitrary (IntMap a) where
+  arbitrary = do{ ks <- arbitrary
+                ; xs <- arbitrary
+                ; return (fromList (zip xs ks))
+                }
+
+
+------------------------------------------------------------------------
+
+type UMap = IntMap ()
+type IMap = IntMap Int
+type SMap = IntMap String
+
+----------------------------------------------------------------
+
+tests :: [Test]
+tests = [ testGroup "Test Case" [
+             ]
+        , testGroup "Property Test" [
+             ]
+        ]
+
+
+----------------------------------------------------------------
+-- Unit tests
+----------------------------------------------------------------
+
+----------------------------------------------------------------
+-- Operators
+
+test_index :: Assertion
+test_index = fromList [(5,'a'), (3,'b')] ! 5 @?= 'a'
+
+----------------------------------------------------------------
+-- Query
+
+test_size :: Assertion
+test_size = do
+    null (empty)           @?= True
+    null (singleton 1 'a') @?= False
+
+test_size2 :: Assertion
+test_size2 = do
+    size empty                                   @?= 0
+    size (singleton 1 'a')                       @?= 1
+    size (fromList([(1,'a'), (2,'c'), (3,'b')])) @?= 3
+
+test_member :: Assertion
+test_member = do
+    member 5 (fromList [(5,'a'), (3,'b')]) @?= True
+    member 1 (fromList [(5,'a'), (3,'b')]) @?= False
+
+test_notMember :: Assertion
+test_notMember = do
+    notMember 5 (fromList [(5,'a'), (3,'b')]) @?= False
+    notMember 1 (fromList [(5,'a'), (3,'b')]) @?= True
+
+test_lookup :: Assertion
+test_lookup = do
+    employeeCurrency 1 @?= Just 1
+    employeeCurrency 2 @?= Nothing
+  where
+    employeeDept = fromList([(1,2), (3,1)])
+    deptCountry = fromList([(1,1), (2,2)])
+    countryCurrency = fromList([(1, 2), (2, 1)])
+    employeeCurrency :: Int -> Maybe Int
+    employeeCurrency name = do
+        dept <- lookup name employeeDept
+        country <- lookup dept deptCountry
+        lookup country countryCurrency
+
+test_findWithDefault :: Assertion
+test_findWithDefault = do
+    findWithDefault 'x' 1 (fromList [(5,'a'), (3,'b')]) @?= 'x'
+    findWithDefault 'x' 5 (fromList [(5,'a'), (3,'b')]) @?= 'a'
+
+test_lookupLT :: Assertion
+test_lookupLT = do
+    lookupLT 3 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+    lookupLT 4 (fromList [(3,'a'), (5,'b')]) @?= Just (3, 'a')
+
+test_lookupGT :: Assertion
+test_lookupGT = do
+    lookupGT 4 (fromList [(3,'a'), (5,'b')]) @?= Just (5, 'b')
+    lookupGT 5 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+
+test_lookupLE :: Assertion
+test_lookupLE = do
+    lookupLE 2 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+    lookupLE 4 (fromList [(3,'a'), (5,'b')]) @?= Just (3, 'a')
+    lookupLE 5 (fromList [(3,'a'), (5,'b')]) @?= Just (5, 'b')
+
+test_lookupGE :: Assertion
+test_lookupGE = do
+    lookupGE 3 (fromList [(3,'a'), (5,'b')]) @?= Just (3, 'a')
+    lookupGE 4 (fromList [(3,'a'), (5,'b')]) @?= Just (5, 'b')
+    lookupGE 6 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+
+----------------------------------------------------------------
+-- Construction
+
+test_empty :: Assertion
+test_empty = do
+    (empty :: UMap)  @?= fromList []
+    size empty @?= 0
+
+test_mempty :: Assertion
+test_mempty = do
+    (mempty :: UMap)  @?= fromList []
+    size (mempty :: UMap) @?= 0
+
+test_singleton :: Assertion
+test_singleton = do
+    singleton 1 'a'        @?= fromList [(1, 'a')]
+    size (singleton 1 'a') @?= 1
+
+test_insert :: Assertion
+test_insert = do
+    insert 5 'x' (fromList [(5,'a'), (3,'b')]) @?= fromList [(3, 'b'), (5, 'x')]
+    insert 7 'x' (fromList [(5,'a'), (3,'b')]) @?= fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+    insert 5 'x' empty                         @?= singleton 5 'x'
+
+test_insertWith :: Assertion
+test_insertWith = do
+    insertWith (++) 5 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "xxxa")]
+    insertWith (++) 7 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a"), (7, "xxx")]
+    insertWith (++) 5 "xxx" empty                         @?= singleton 5 "xxx"
+
+test_insertWithKey :: Assertion
+test_insertWithKey = do
+    insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "5:xxx|a")]
+    insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a"), (7, "xxx")]
+    insertWithKey f 5 "xxx" empty                         @?= singleton 5 "xxx"
+  where
+    f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+
+test_insertLookupWithKey :: Assertion
+test_insertLookupWithKey = do
+    insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) @?= (Just "a", fromList [(3, "b"), (5, "5:xxx|a")])
+    insertLookupWithKey f 2 "xxx" (fromList [(5,"a"), (3,"b")]) @?= (Nothing,fromList [(2,"xxx"),(3,"b"),(5,"a")])
+    insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) @?= (Nothing,  fromList [(3, "b"), (5, "a"), (7, "xxx")])
+    insertLookupWithKey f 5 "xxx" empty                         @?= (Nothing,  singleton 5 "xxx")
+  where
+    f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+
+----------------------------------------------------------------
+-- Delete/Update
+
+test_delete :: Assertion
+test_delete = do
+    delete 5 (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+    delete 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    delete 5 empty                         @?= (empty :: IMap)
+
+test_adjust :: Assertion
+test_adjust = do
+    adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "new a")]
+    adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    adjust ("new " ++) 7 empty                         @?= empty
+
+test_adjustWithKey :: Assertion
+test_adjustWithKey = do
+    adjustWithKey f 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "5:new a")]
+    adjustWithKey f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    adjustWithKey f 7 empty                         @?= empty
+  where
+    f key x = (show key) ++ ":new " ++ x
+
+test_update :: Assertion
+test_update = do
+    update f 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "new a")]
+    update f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    update f 3 (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+  where
+    f x = if x == "a" then Just "new a" else Nothing
+
+test_updateWithKey :: Assertion
+test_updateWithKey = do
+    updateWithKey f 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "5:new a")]
+    updateWithKey f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    updateWithKey f 3 (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+ where
+     f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+
+test_updateLookupWithKey :: Assertion
+test_updateLookupWithKey = do
+    updateLookupWithKey f 5 (fromList [(5,"a"), (3,"b")]) @?= (Just "a", fromList [(3, "b"), (5, "5:new a")])
+    updateLookupWithKey f 7 (fromList [(5,"a"), (3,"b")]) @?= (Nothing,  fromList [(3, "b"), (5, "a")])
+    updateLookupWithKey f 3 (fromList [(5,"a"), (3,"b")]) @?= (Just "b", singleton 5 "a")
+  where
+    f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+
+test_alter :: Assertion
+test_alter = do
+    alter f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    alter f 5 (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+    alter g 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a"), (7, "c")]
+    alter g 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "c")]
+  where
+    f _ = Nothing
+    g _ = Just "c"
+
+----------------------------------------------------------------
+-- Combine
+
+test_union :: Assertion
+test_union = union (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+
+test_mappend :: Assertion
+test_mappend = mappend (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+
+test_unionWith :: Assertion
+test_unionWith = unionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "aA"), (7, "C")]
+
+test_unionWithKey :: Assertion
+test_unionWithKey = unionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "5:a|A"), (7, "C")]
+  where
+    f key left_value right_value = (show key) ++ ":" ++ left_value ++ "|" ++ right_value
+
+test_unions :: Assertion
+test_unions = do
+    unions [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+        @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+    unions [(fromList [(5, "A3"), (3, "B3")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "a"), (3, "b")])]
+        @?= fromList [(3, "B3"), (5, "A3"), (7, "C")]
+
+test_mconcat :: Assertion
+test_mconcat = do
+    mconcat [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+        @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+    mconcat [(fromList [(5, "A3"), (3, "B3")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "a"), (3, "b")])]
+        @?= fromList [(3, "B3"), (5, "A3"), (7, "C")]
+
+test_unionsWith :: Assertion
+test_unionsWith = unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+     @?= fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
+
+test_difference :: Assertion
+test_difference = difference (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 3 "b"
+
+test_differenceWith :: Assertion
+test_differenceWith = differenceWith f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (7, "C")])
+     @?= singleton 3 "b:B"
+ where
+   f al ar = if al== "b" then Just (al ++ ":" ++ ar) else Nothing
+
+test_differenceWithKey :: Assertion
+test_differenceWithKey = differenceWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (10, "C")])
+     @?= singleton 3 "3:b|B"
+  where
+    f k al ar = if al == "b" then Just ((show k) ++ ":" ++ al ++ "|" ++ ar) else Nothing
+
+test_intersection :: Assertion
+test_intersection = intersection (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 5 "a"
+
+
+test_intersectionWith :: Assertion
+test_intersectionWith = intersectionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 5 "aA"
+
+test_intersectionWithKey :: Assertion
+test_intersectionWithKey = intersectionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 5 "5:a|A"
+  where
+    f k al ar = (show k) ++ ":" ++ al ++ "|" ++ ar
+
+----------------------------------------------------------------
+-- Traversal
+
+test_map :: Assertion
+test_map = map (++ "x") (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "bx"), (5, "ax")]
+
+test_mapWithKey :: Assertion
+test_mapWithKey = mapWithKey f (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "3:b"), (5, "5:a")]
+  where
+    f key x = (show key) ++ ":" ++ x
+
+test_mapAccum :: Assertion
+test_mapAccum = mapAccum f "Everything: " (fromList [(5,"a"), (3,"b")]) @?= ("Everything: ba", fromList [(3, "bX"), (5, "aX")])
+  where
+    f a b = (a ++ b, b ++ "X")
+
+test_mapAccumWithKey :: Assertion
+test_mapAccumWithKey = mapAccumWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) @?= ("Everything: 3-b 5-a", fromList [(3, "bX"), (5, "aX")])
+  where
+    f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+
+test_mapAccumRWithKey :: Assertion
+test_mapAccumRWithKey = mapAccumRWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) @?= ("Everything: 5-a 3-b", fromList [(3, "bX"), (5, "aX")])
+  where
+    f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+
+test_mapKeys :: Assertion
+test_mapKeys = do
+    mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])                        @?= fromList [(4, "b"), (6, "a")]
+    mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 1 "c"
+    mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 3 "c"
+
+test_mapKeysWith :: Assertion
+test_mapKeysWith = do
+    mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 1 "cdab"
+    mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 3 "cdab"
+
+test_mapKeysMonotonic :: Assertion
+test_mapKeysMonotonic = do
+    mapKeysMonotonic (+ 1) (fromList [(5,"a"), (3,"b")])          @?= fromList [(4, "b"), (6, "a")]
+    mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")]) @?= fromList [(6, "b"), (10, "a")]
+
+----------------------------------------------------------------
+-- Conversion
+
+test_elems :: Assertion
+test_elems = do
+    elems (fromList [(5,"a"), (3,"b")]) @?= ["b","a"]
+    elems (empty :: UMap) @?= []
+
+test_keys :: Assertion
+test_keys = do
+    keys (fromList [(5,"a"), (3,"b")]) @?= [3,5]
+    keys (empty :: UMap) @?= []
+
+test_assocs :: Assertion
+test_assocs = do
+    assocs (fromList [(5,"a"), (3,"b")]) @?= [(3,"b"), (5,"a")]
+    assocs (empty :: UMap) @?= []
+
+test_keysSet :: Assertion
+test_keysSet = do
+    keysSet (fromList [(5,"a"), (3,"b")]) @?= Data.IntSet.fromList [3,5]
+    keysSet (empty :: UMap) @?= Data.IntSet.empty
+
+test_fromSet :: Assertion
+test_fromSet = do
+   fromSet (\k -> replicate k 'a') (Data.IntSet.fromList [3, 5]) @?= fromList [(5,"aaaaa"), (3,"aaa")]
+   fromSet undefined Data.IntSet.empty @?= (empty :: IMap)
+
+----------------------------------------------------------------
+-- Lists
+
+test_toList :: Assertion
+test_toList = do
+    toList (fromList [(5,"a"), (3,"b")]) @?= [(3,"b"), (5,"a")]
+    toList (empty :: SMap) @?= []
+
+test_fromList :: Assertion
+test_fromList = do
+    fromList [] @?= (empty :: SMap)
+    fromList [(5,"a"), (3,"b"), (5, "c")] @?= fromList [(5,"c"), (3,"b")]
+    fromList [(5,"c"), (3,"b"), (5, "a")] @?= fromList [(5,"a"), (3,"b")]
+
+test_fromListWith :: Assertion
+test_fromListWith = do
+    fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] @?= fromList [(3, "ab"), (5, "aba")]
+    fromListWith (++) [] @?= (empty :: SMap)
+
+test_fromListWithKey :: Assertion
+test_fromListWithKey = do
+    fromListWithKey f [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] @?= fromList [(3, "3ab"), (5, "5a5ba")]
+    fromListWithKey f [] @?= (empty :: SMap)
+  where
+    f k a1 a2 = (show k) ++ a1 ++ a2
+
+----------------------------------------------------------------
+-- Ordered lists
+
+test_toAscList :: Assertion
+test_toAscList = toAscList (fromList [(5,"a"), (3,"b")]) @?= [(3,"b"), (5,"a")]
+
+test_toDescList :: Assertion
+test_toDescList = toDescList (fromList [(5,"a"), (3,"b")]) @?= [(5,"a"), (3,"b")]
+
+test_showTree :: Assertion
+test_showTree =
+       (let t = fromDistinctAscList [(x,()) | x <- [1..5]]
+        in showTree t) @?= "*\n+--*\n|  +-- 1:=()\n|  +--*\n|     +-- 2:=()\n|     +-- 3:=()\n+--*\n   +-- 4:=()\n   +-- 5:=()\n"
+
+test_fromAscList :: Assertion
+test_fromAscList = do
+    fromAscList [(3,"b"), (5,"a")]          @?= fromList [(3, "b"), (5, "a")]
+    fromAscList [(3,"b"), (5,"a"), (5,"b")] @?= fromList [(3, "b"), (5, "b")]
+
+
+test_fromAscListWith :: Assertion
+test_fromAscListWith = do
+    fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] @?= fromList [(3, "b"), (5, "ba")]
+
+test_fromAscListWithKey :: Assertion
+test_fromAscListWithKey = do
+    fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")] @?= fromList [(3, "b"), (5, "5:b5:ba")]
+  where
+    f k a1 a2 = (show k) ++ ":" ++ a1 ++ a2
+
+test_fromDistinctAscList :: Assertion
+test_fromDistinctAscList = do
+    fromDistinctAscList [(3,"b"), (5,"a")] @?= fromList [(3, "b"), (5, "a")]
+
+----------------------------------------------------------------
+-- Filter
+
+test_filter :: Assertion
+test_filter = do
+    filter (> "a") (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+    filter (> "x") (fromList [(5,"a"), (3,"b")]) @?= empty
+    filter (< "a") (fromList [(5,"a"), (3,"b")]) @?= empty
+
+test_filteWithKey :: Assertion
+test_filteWithKey = filterWithKey (\k _ -> k > 4) (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+
+test_partition :: Assertion
+test_partition = do
+    partition (> "a") (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", singleton 5 "a")
+    partition (< "x") (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3, "b"), (5, "a")], empty)
+    partition (> "x") (fromList [(5,"a"), (3,"b")]) @?= (empty, fromList [(3, "b"), (5, "a")])
+
+test_partitionWithKey :: Assertion
+test_partitionWithKey = do
+    partitionWithKey (\ k _ -> k > 3) (fromList [(5,"a"), (3,"b")]) @?= (singleton 5 "a", singleton 3 "b")
+    partitionWithKey (\ k _ -> k < 7) (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3, "b"), (5, "a")], empty)
+    partitionWithKey (\ k _ -> k > 7) (fromList [(5,"a"), (3,"b")]) @?= (empty, fromList [(3, "b"), (5, "a")])
+
+test_mapMaybe :: Assertion
+test_mapMaybe = mapMaybe f (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "new a"
+  where
+    f x = if x == "a" then Just "new a" else Nothing
+
+test_mapMaybeWithKey :: Assertion
+test_mapMaybeWithKey = mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "key : 3"
+  where
+    f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
+
+test_mapEither :: Assertion
+test_mapEither = do
+    mapEither f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+        @?= (fromList [(3,"b"), (5,"a")], fromList [(1,"x"), (7,"z")])
+    mapEither (\ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+        @?= ((empty :: SMap), fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+ where
+   f a = if a < "c" then Left a else Right a
+
+test_mapEitherWithKey :: Assertion
+test_mapEitherWithKey = do
+    mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+     @?= (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])
+    mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+     @?= ((empty :: SMap), fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])
+  where
+    f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
+
+test_split :: Assertion
+test_split = do
+    split 2 (fromList [(5,"a"), (3,"b")]) @?= (empty, fromList [(3,"b"), (5,"a")])
+    split 3 (fromList [(5,"a"), (3,"b")]) @?= (empty, singleton 5 "a")
+    split 4 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", singleton 5 "a")
+    split 5 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", empty)
+    split 6 (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3,"b"), (5,"a")], empty)
+
+test_splitLookup :: Assertion
+test_splitLookup = do
+    splitLookup 2 (fromList [(5,"a"), (3,"b")]) @?= (empty, Nothing, fromList [(3,"b"), (5,"a")])
+    splitLookup 3 (fromList [(5,"a"), (3,"b")]) @?= (empty, Just "b", singleton 5 "a")
+    splitLookup 4 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", Nothing, singleton 5 "a")
+    splitLookup 5 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", Just "a", empty)
+    splitLookup 6 (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3,"b"), (5,"a")], Nothing, empty)
+
+----------------------------------------------------------------
+-- Submap
+
+test_isSubmapOfBy :: Assertion
+test_isSubmapOfBy = do
+    isSubmapOfBy (==) (fromList [(fromEnum 'a',1)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= True
+    isSubmapOfBy (<=) (fromList [(fromEnum 'a',1)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= True
+    isSubmapOfBy (==) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= True
+    isSubmapOfBy (==) (fromList [(fromEnum 'a',2)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= False
+    isSubmapOfBy (<)  (fromList [(fromEnum 'a',1)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= False
+    isSubmapOfBy (==) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) (fromList [(fromEnum 'a',1)]) @?= False
+
+test_isSubmapOf :: Assertion
+test_isSubmapOf = do
+    isSubmapOf (fromList [(fromEnum 'a',1)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= True
+    isSubmapOf (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= True
+    isSubmapOf (fromList [(fromEnum 'a',2)]) (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) @?= False
+    isSubmapOf (fromList [(fromEnum 'a',1),(fromEnum 'b',2)]) (fromList [(fromEnum 'a',1)]) @?= False
+
+test_isProperSubmapOfBy :: Assertion
+test_isProperSubmapOfBy = do
+    isProperSubmapOfBy (==) (fromList [(1,1)]) (fromList [(1,1),(2,2)]) @?= True
+    isProperSubmapOfBy (<=) (fromList [(1,1)]) (fromList [(1,1),(2,2)]) @?= True
+    isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)]) @?= False
+    isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1)]) @?= False
+    isProperSubmapOfBy (<)  (fromList [(1,1)])       (fromList [(1,1),(2,2)]) @?= False
+
+test_isProperSubmapOf :: Assertion
+test_isProperSubmapOf = do
+    isProperSubmapOf (fromList [(1,1)]) (fromList [(1,1),(2,2)]) @?= True
+    isProperSubmapOf (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)]) @?= False
+    isProperSubmapOf (fromList [(1,1),(2,2)]) (fromList [(1,1)]) @?= False
+
+----------------------------------------------------------------
+-- Min/Max
+
+test_findMin :: Assertion
+test_findMin = findMin (fromList [(5,"a"), (3,"b")]) @?= (3,"b")
+
+test_findMax :: Assertion
+test_findMax = findMax (fromList [(5,"a"), (3,"b")]) @?= (5,"a")
+
+test_deleteMin :: Assertion
+test_deleteMin = do
+    deleteMin (fromList [(5,"a"), (3,"b"), (7,"c")]) @?= fromList [(5,"a"), (7,"c")]
+    deleteMin (empty :: SMap) @?= empty
+
+test_deleteMax :: Assertion
+test_deleteMax = do
+    deleteMax (fromList [(5,"a"), (3,"b"), (7,"c")]) @?= fromList [(3,"b"), (5,"a")]
+    deleteMax (empty :: SMap) @?= empty
+
+test_deleteFindMin :: Assertion
+test_deleteFindMin = deleteFindMin (fromList [(5,"a"), (3,"b"), (10,"c")]) @?= ((3,"b"), fromList[(5,"a"), (10,"c")])
+
+test_deleteFindMax :: Assertion
+test_deleteFindMax = deleteFindMax (fromList [(5,"a"), (3,"b"), (10,"c")]) @?= ((10,"c"), fromList [(3,"b"), (5,"a")])
+
+test_updateMin :: Assertion
+test_updateMin = do
+    updateMin (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "Xb"), (5, "a")]
+    updateMin (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+
+test_updateMax :: Assertion
+test_updateMax = do
+    updateMax (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "Xa")]
+    updateMax (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+
+test_updateMinWithKey :: Assertion
+test_updateMinWithKey = do
+    updateMinWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3,"3:b"), (5,"a")]
+    updateMinWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+
+test_updateMaxWithKey :: Assertion
+test_updateMaxWithKey = do
+    updateMaxWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3,"b"), (5,"5:a")]
+    updateMaxWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+
+test_minView :: Assertion
+test_minView = do
+    minView (fromList [(5,"a"), (3,"b")]) @?= Just ("b", singleton 5 "a")
+    minView (empty :: SMap) @?= Nothing
+
+test_maxView :: Assertion
+test_maxView = do
+    maxView (fromList [(5,"a"), (3,"b")]) @?= Just ("a", singleton 3 "b")
+    maxView (empty :: SMap) @?= Nothing
+
+test_minViewWithKey :: Assertion
+test_minViewWithKey = do
+    minViewWithKey (fromList [(5,"a"), (3,"b")]) @?= Just ((3,"b"), singleton 5 "a")
+    minViewWithKey (empty :: SMap) @?= Nothing
+
+test_maxViewWithKey :: Assertion
+test_maxViewWithKey = do
+    maxViewWithKey (fromList [(5,"a"), (3,"b")]) @?= Just ((5,"a"), singleton 3 "b")
+    maxViewWithKey (empty :: SMap) @?= Nothing
+
+----------------------------------------------------------------
+-- QuickCheck
+----------------------------------------------------------------
+
+prop_singleton :: Int -> Int -> Bool
+prop_singleton k x = insert k x empty == singleton k x
+
+prop_insertLookup :: Int -> UMap -> Bool
+prop_insertLookup k t = lookup k (insert k () t) /= Nothing
+
+prop_insertDelete :: Int -> UMap -> Property
+prop_insertDelete k t = (lookup k t == Nothing) ==> (delete k (insert k () t) == t)
+
+prop_deleteNonMember :: Int -> UMap -> Property
+prop_deleteNonMember k t = (lookup k t == Nothing) ==> (delete k t == t)
+
+----------------------------------------------------------------
+
+prop_unionModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_unionModel xs ys
+  = sort (keys (union (fromList xs) (fromList ys)))
+    == sort (nub (Prelude.map fst xs ++ Prelude.map fst ys))
+
+prop_unionSingleton :: IMap -> Int -> Int -> Bool
+prop_unionSingleton t k x = union (singleton k x) t == insert k x t
+
+prop_unionAssoc :: IMap -> IMap -> IMap -> Bool
+prop_unionAssoc t1 t2 t3 = union t1 (union t2 t3) == union (union t1 t2) t3
+
+prop_unionWith :: IMap -> IMap -> Bool
+prop_unionWith t1 t2 = (union t1 t2 == unionWith (\_ y -> y) t2 t1)
+
+prop_unionSum :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_unionSum xs ys
+  = sum (elems (unionWith (+) (fromListWith (+) xs) (fromListWith (+) ys)))
+    == (sum (Prelude.map snd xs) + sum (Prelude.map snd ys))
+
+prop_differenceModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_differenceModel xs ys
+  = sort (keys (difference (fromListWith (+) xs) (fromListWith (+) ys)))
+    == sort ((List.\\) (nub (Prelude.map fst xs)) (nub (Prelude.map fst ys)))
+
+prop_intersectionModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_intersectionModel xs ys
+  = sort (keys (intersection (fromListWith (+) xs) (fromListWith (+) ys)))
+    == sort (nub ((List.intersect) (Prelude.map fst xs) (Prelude.map fst ys)))
+
+prop_intersectionWithModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_intersectionWithModel xs ys
+  = toList (intersectionWith f (fromList xs') (fromList ys'))
+    == [(kx, f vx vy ) | (kx, vx) <- List.sort xs', (ky, vy) <- ys', kx == ky]
+    where xs' = List.nubBy ((==) `on` fst) xs
+          ys' = List.nubBy ((==) `on` fst) ys
+          f l r = l + 2 * r
+
+prop_intersectionWithKeyModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_intersectionWithKeyModel xs ys
+  = toList (intersectionWithKey f (fromList xs') (fromList ys'))
+    == [(kx, f kx vx vy) | (kx, vx) <- List.sort xs', (ky, vy) <- ys', kx == ky]
+    where xs' = List.nubBy ((==) `on` fst) xs
+          ys' = List.nubBy ((==) `on` fst) ys
+          f k l r = k + 2 * l + 3 * r
+
+prop_mergeWithKeyModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_mergeWithKeyModel xs ys
+  = and [ testMergeWithKey f keep_x keep_y
+        | f <- [ \_k x1  _x2 -> Just x1
+               , \_k _x1 x2  -> Just x2
+               , \_k _x1 _x2 -> Nothing
+               , \k  x1  x2  -> if k `mod` 2 == 0 then Nothing else Just (2 * x1 + 3 * x2)
+               ]
+        , keep_x <- [ True, False ]
+        , keep_y <- [ True, False ]
+        ]
+
+    where xs' = List.nubBy ((==) `on` fst) xs
+          ys' = List.nubBy ((==) `on` fst) ys
+
+          xm = fromList xs'
+          ym = fromList ys'
+
+          testMergeWithKey f keep_x keep_y
+            = toList (mergeWithKey f (keep keep_x) (keep keep_y) xm ym) == emulateMergeWithKey f keep_x keep_y
+              where keep False _ = empty
+                    keep True  m = m
+
+                    emulateMergeWithKey f keep_x keep_y
+                      = Maybe.mapMaybe combine (sort $ List.union (List.map fst xs') (List.map fst ys'))
+                        where combine k = case (List.lookup k xs', List.lookup k ys') of
+                                            (Nothing, Just y) -> if keep_y then Just (k, y) else Nothing
+                                            (Just x, Nothing) -> if keep_x then Just (k, x) else Nothing
+                                            (Just x, Just y) -> (\v -> (k, v)) `fmap` f k x y
+
+          -- We prevent inlining testMergeWithKey to disable the SpecConstr
+          -- optimalization. There are too many call patterns here so several
+          -- warnings are issued if testMergeWithKey gets inlined.
+          {-# NOINLINE testMergeWithKey #-}
+
+----------------------------------------------------------------
+
+prop_ordered :: Property
+prop_ordered
+  = forAll (choose (5,100)) $ \n ->
+    let xs = [(x,()) | x <- [0..n::Int]]
+    in fromAscList xs == fromList xs
+
+prop_list :: [Int] -> Bool
+prop_list xs = (sort (nub xs) == [x | (x,()) <- toList (fromList [(x,()) | x <- xs])])
+
+prop_descList :: [Int] -> Bool
+prop_descList xs = (reverse (sort (nub xs)) == [x | (x,()) <- toDescList (fromList [(x,()) | x <- xs])])
+
+prop_ascDescList :: [Int] -> Bool
+prop_ascDescList xs = toAscList m == reverse (toDescList m)
+  where m = fromList $ zip xs $ repeat ()
+
+prop_fromList :: [Int] -> Bool
+prop_fromList xs
+  = case fromList (zip xs xs) of
+      t -> t == fromAscList (zip sort_xs sort_xs) &&
+           t == fromDistinctAscList (zip nub_sort_xs nub_sort_xs) &&
+           t == List.foldr (uncurry insert) empty (zip xs xs)
+  where sort_xs = sort xs
+        nub_sort_xs = List.map List.head $ List.group sort_xs
+
+----------------------------------------------------------------
+
+prop_alter :: UMap -> Int -> Bool
+prop_alter t k = case lookup k t of
+    Just _  -> (size t - 1) == size t' && lookup k t' == Nothing
+    Nothing -> (size t + 1) == size t' && lookup k t' /= Nothing
+  where
+    t' = alter f k t
+    f Nothing   = Just ()
+    f (Just ()) = Nothing
+
+------------------------------------------------------------------------
+-- Compare against the list model (after nub on keys)
+
+prop_index :: [Int] -> Property
+prop_index xs = length xs > 0 ==>
+  let m  = fromList (zip xs xs)
+  in  xs == [ m ! i | i <- xs ]
+
+prop_null :: IMap -> Bool
+prop_null m = null m == (size m == 0)
+
+prop_member :: [Int] -> Int -> Bool
+prop_member xs n =
+  let m  = fromList (zip xs xs)
+  in all (\k -> k `member` m == (k `elem` xs)) (n : xs)
+
+prop_notmember :: [Int] -> Int -> Bool
+prop_notmember xs n =
+  let m  = fromList (zip xs xs)
+  in all (\k -> k `notMember` m == (k `notElem` xs)) (n : xs)
+
+prop_lookup :: [(Int, Int)] -> Int -> Bool
+prop_lookup xs n =
+  let xs' = List.nubBy ((==) `on` fst) xs
+      m = fromList xs'
+  in all (\k -> lookup k m == List.lookup k xs') (n : List.map fst xs')
+
+prop_find :: [(Int, Int)] -> Bool
+prop_find xs =
+  let xs' = List.nubBy ((==) `on` fst) xs
+      m = fromList xs'
+  in all (\(k, v) -> m ! k == v) xs'
+
+prop_findWithDefault :: [(Int, Int)] -> Int -> Int -> Bool
+prop_findWithDefault xs n x =
+  let xs' = List.nubBy ((==) `on` fst) xs
+      m = fromList xs'
+  in all (\k -> findWithDefault x k m == maybe x id (List.lookup k xs')) (n : List.map fst xs')
+
+test_lookupSomething :: (Int -> IntMap Int -> Maybe (Int, Int)) -> (Int -> Int -> Bool) -> [(Int, Int)] -> Bool
+test_lookupSomething lookup' cmp xs =
+  let odd_sorted_xs = filter_odd $ sort $ List.nubBy ((==) `on` fst) xs
+      t = fromList odd_sorted_xs
+      test k = case List.filter ((`cmp` k) . fst) odd_sorted_xs of
+                 []             -> lookup' k t == Nothing
+                 cs | 0 `cmp` 1 -> lookup' k t == Just (last cs) -- we want largest such element
+                    | otherwise -> lookup' k t == Just (head cs) -- we want smallest such element
+  in all test (List.map fst xs)
+
+  where filter_odd [] = []
+        filter_odd [_] = []
+        filter_odd (_ : o : xs) = o : filter_odd xs
+
+prop_lookupLT :: [(Int, Int)] -> Bool
+prop_lookupLT = test_lookupSomething lookupLT (<)
+
+prop_lookupGT :: [(Int, Int)] -> Bool
+prop_lookupGT = test_lookupSomething lookupGT (>)
+
+prop_lookupLE :: [(Int, Int)] -> Bool
+prop_lookupLE = test_lookupSomething lookupLE (<=)
+
+prop_lookupGE :: [(Int, Int)] -> Bool
+prop_lookupGE = test_lookupSomething lookupGE (>=)
+
+prop_findMin :: [(Int, Int)] -> Property
+prop_findMin ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  findMin m == List.minimumBy (comparing fst) xs
+
+prop_findMax :: [(Int, Int)] -> Property
+prop_findMax ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  findMax m == List.maximumBy (comparing fst) xs
+
+prop_deleteMinModel :: [(Int, Int)] -> Property
+prop_deleteMinModel ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  toAscList (deleteMin m) == tail (sort xs)
+
+prop_deleteMaxModel :: [(Int, Int)] -> Property
+prop_deleteMaxModel ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  toAscList (deleteMax m) == init (sort xs)
+
+prop_filter :: (Int -> Bool) -> [(Int, Int)] -> Property
+prop_filter p ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  filter p m == fromList (List.filter (p . snd) xs)
+
+prop_partition :: (Int -> Bool) -> [(Int, Int)] -> Property
+prop_partition p ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  partition p m == let (a,b) = (List.partition (p . snd) xs) in (fromList a, fromList b)
+
+prop_map :: (Int -> Int) -> [(Int, Int)] -> Property
+prop_map f ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  map f m == fromList [ (a, f b) | (a,b) <- xs ]
+
+prop_fmap :: (Int -> Int) -> [(Int, Int)] -> Property
+prop_fmap f ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  fmap f m == fromList [ (a, f b) | (a,b) <- xs ]
+
+prop_mapkeys :: (Int -> Int) -> [(Int, Int)] -> Property
+prop_mapkeys f ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  mapKeys f m == (fromList $ List.nubBy ((==) `on` fst) $ reverse [ (f a, b) | (a,b) <- sort xs])
+
+prop_splitModel :: Int -> [(Int, Int)] -> Property
+prop_splitModel n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      (l, r) = split n $ fromList xs
+  in  toAscList l == sort [(k, v) | (k,v) <- xs, k < n] &&
+      toAscList r == sort [(k, v) | (k,v) <- xs, k > n]
+
+prop_splitRoot :: IMap -> Bool
+prop_splitRoot s = loop ls && (s == unions ls)
+ where
+  ls = splitRoot s
+  loop [] = True
+  loop (s1:rst) = List.null
+                  [ (x,y) | x <- toList s1
+                          , y <- toList (unions rst)
+                          , x > y ]
+
+prop_foldr :: Int -> [(Int, Int)] -> Property
+prop_foldr n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldr (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldr (:) [] m == List.map snd (List.sort xs) &&
+      foldrWithKey (\_ a b -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldrWithKey (\k _ b -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldrWithKey (\k x xs -> (k,x):xs) [] m == List.sort xs
+
+
+prop_foldr' :: Int -> [(Int, Int)] -> Property
+prop_foldr' n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldr' (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldr' (:) [] m == List.map snd (List.sort xs) &&
+      foldrWithKey' (\_ a b -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldrWithKey' (\k _ b -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldrWithKey' (\k x xs -> (k,x):xs) [] m == List.sort xs
+
+prop_foldl :: Int -> [(Int, Int)] -> Property
+prop_foldl n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldl (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldl (flip (:)) [] m == reverse (List.map snd (List.sort xs)) &&
+      foldlWithKey (\b _ a -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldlWithKey (\b k _ -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldlWithKey (\xs k x -> (k,x):xs) [] m == reverse (List.sort xs)
+
+prop_foldl' :: Int -> [(Int, Int)] -> Property
+prop_foldl' n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldl' (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldl' (flip (:)) [] m == reverse (List.map snd (List.sort xs)) &&
+      foldlWithKey' (\b _ a -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldlWithKey' (\b k _ -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldlWithKey' (\xs k x -> (k,x):xs) [] m == reverse (List.sort xs)
+
+prop_keysSet :: [(Int, Int)] -> Bool
+prop_keysSet xs =
+  keysSet (fromList xs) == Data.IntSet.fromList (List.map fst xs)
+
+prop_fromSet :: [(Int, Int)] -> Bool
+prop_fromSet ys =
+  let xs = List.nubBy ((==) `on` fst) ys
+  in fromSet (\k -> fromJust $ List.lookup k xs) (Data.IntSet.fromList $ List.map fst xs) == fromList xs
diff --git a/tests/intset-properties.hs b/tests/intset-properties.hs
new file mode 100644
--- /dev/null
+++ b/tests/intset-properties.hs
@@ -0,0 +1,337 @@
+{-# LANGUAGE CPP #-}
+#if MIN_VERSION_base(4,5,0)
+import Data.Bits ((.&.), popCount)
+import Data.Word (Word)
+#else
+import Data.Bits ((.&.))
+#endif
+import Data.IntSet
+import Data.List (nub,sort)
+import qualified Data.List as List
+import Data.Monoid (mempty)
+import qualified Data.Set as Set
+import Prelude hiding (lookup, null, map, filter, foldr, foldl)
+import Test.Framework
+import Test.Framework.Providers.HUnit
+import Test.Framework.Providers.QuickCheck2
+import Test.HUnit hiding (Test, Testable)
+import Test.QuickCheck hiding ((.&.))
+
+main :: IO ()
+main = defaultMain [ testCase "lookupLT" test_lookupLT
+                   , testCase "lookupGT" test_lookupGT
+                   , testCase "lookupLE" test_lookupLE
+                   , testCase "lookupGE" test_lookupGE
+                   , testCase "split" test_split
+                   , testProperty "prop_Single" prop_Single
+                   , testProperty "prop_Member" prop_Member
+                   , testProperty "prop_NotMember" prop_NotMember
+                   , testProperty "prop_LookupLT" prop_LookupLT
+                   , testProperty "prop_LookupGT" prop_LookupGT
+                   , testProperty "prop_LookupLE" prop_LookupLE
+                   , testProperty "prop_LookupGE" prop_LookupGE
+                   , testProperty "prop_InsertDelete" prop_InsertDelete
+                   , testProperty "prop_MemberFromList" prop_MemberFromList
+                   , testProperty "prop_UnionInsert" prop_UnionInsert
+                   , testProperty "prop_UnionAssoc" prop_UnionAssoc
+                   , testProperty "prop_UnionComm" prop_UnionComm
+                   , testProperty "prop_Diff" prop_Diff
+                   , testProperty "prop_Int" prop_Int
+                   , testProperty "prop_Ordered" prop_Ordered
+                   , testProperty "prop_List" prop_List
+                   , testProperty "prop_DescList" prop_DescList
+                   , testProperty "prop_AscDescList" prop_AscDescList
+                   , testProperty "prop_fromList" prop_fromList
+                   , testProperty "prop_MaskPow2" prop_MaskPow2
+                   , testProperty "prop_Prefix" prop_Prefix
+                   , testProperty "prop_LeftRight" prop_LeftRight
+                   , testProperty "prop_isProperSubsetOf" prop_isProperSubsetOf
+                   , testProperty "prop_isProperSubsetOf2" prop_isProperSubsetOf2
+                   , testProperty "prop_isSubsetOf" prop_isSubsetOf
+                   , testProperty "prop_isSubsetOf2" prop_isSubsetOf2
+                   , testProperty "prop_size" prop_size
+                   , testProperty "prop_findMax" prop_findMax
+                   , testProperty "prop_findMin" prop_findMin
+                   , testProperty "prop_ord" prop_ord
+                   , testProperty "prop_readShow" prop_readShow
+                   , testProperty "prop_foldR" prop_foldR
+                   , testProperty "prop_foldR'" prop_foldR'
+                   , testProperty "prop_foldL" prop_foldL
+                   , testProperty "prop_foldL'" prop_foldL'
+                   , testProperty "prop_map" prop_map
+                   , testProperty "prop_maxView" prop_maxView
+                   , testProperty "prop_minView" prop_minView
+                   , testProperty "prop_split" prop_split
+                   , testProperty "prop_splitMember" prop_splitMember
+                   , testProperty "prop_splitRoot" prop_splitRoot
+                   , testProperty "prop_partition" prop_partition
+                   , testProperty "prop_filter" prop_filter
+#if MIN_VERSION_base(4,5,0)
+                   , testProperty "prop_bitcount" prop_bitcount
+#endif
+                   ]
+
+----------------------------------------------------------------
+-- Unit tests
+----------------------------------------------------------------
+
+test_lookupLT :: Assertion
+test_lookupLT = do
+    lookupLT 3 (fromList [3, 5]) @?= Nothing
+    lookupLT 5 (fromList [3, 5]) @?= Just 3
+
+test_lookupGT :: Assertion
+test_lookupGT = do
+   lookupGT 4 (fromList [3, 5]) @?= Just 5
+   lookupGT 5 (fromList [3, 5]) @?= Nothing
+
+test_lookupLE :: Assertion
+test_lookupLE = do
+   lookupLE 2 (fromList [3, 5]) @?= Nothing
+   lookupLE 4 (fromList [3, 5]) @?= Just 3
+   lookupLE 5 (fromList [3, 5]) @?= Just 5
+
+test_lookupGE :: Assertion
+test_lookupGE = do
+   lookupGE 3 (fromList [3, 5]) @?= Just 3
+   lookupGE 4 (fromList [3, 5]) @?= Just 5
+   lookupGE 6 (fromList [3, 5]) @?= Nothing
+
+test_split :: Assertion
+test_split = do
+   split 3 (fromList [1..5]) @?= (fromList [1,2], fromList [4,5])
+
+{--------------------------------------------------------------------
+  Arbitrary, reasonably balanced trees
+--------------------------------------------------------------------}
+instance Arbitrary IntSet where
+  arbitrary = do{ xs <- arbitrary
+                ; return (fromList xs)
+                }
+
+
+{--------------------------------------------------------------------
+  Single, Member, Insert, Delete, Member, FromList
+--------------------------------------------------------------------}
+prop_Single :: Int -> Bool
+prop_Single x
+  = (insert x empty == singleton x)
+
+prop_Member :: [Int] -> Int -> Bool
+prop_Member xs n =
+  let m  = fromList xs
+  in all (\k -> k `member` m == (k `elem` xs)) (n : xs)
+
+prop_NotMember :: [Int] -> Int -> Bool
+prop_NotMember xs n =
+  let m  = fromList xs
+  in all (\k -> k `notMember` m == (k `notElem` xs)) (n : xs)
+
+test_LookupSomething :: (Int -> IntSet -> Maybe Int) -> (Int -> Int -> Bool) -> [Int] -> Bool
+test_LookupSomething lookup' cmp xs =
+  let odd_sorted_xs = filter_odd $ nub $ sort xs
+      t = fromList odd_sorted_xs
+      test x = case List.filter (`cmp` x) odd_sorted_xs of
+                 []             -> lookup' x t == Nothing
+                 cs | 0 `cmp` 1 -> lookup' x t == Just (last cs) -- we want largest such element
+                    | otherwise -> lookup' x t == Just (head cs) -- we want smallest such element
+  in all test xs
+
+  where filter_odd [] = []
+        filter_odd [_] = []
+        filter_odd (_ : o : xs) = o : filter_odd xs
+
+prop_LookupLT :: [Int] -> Bool
+prop_LookupLT = test_LookupSomething lookupLT (<)
+
+prop_LookupGT :: [Int] -> Bool
+prop_LookupGT = test_LookupSomething lookupGT (>)
+
+prop_LookupLE :: [Int] -> Bool
+prop_LookupLE = test_LookupSomething lookupLE (<=)
+
+prop_LookupGE :: [Int] -> Bool
+prop_LookupGE = test_LookupSomething lookupGE (>=)
+
+prop_InsertDelete :: Int -> IntSet -> Property
+prop_InsertDelete k t
+  = not (member k t) ==> delete k (insert k t) == t
+
+prop_MemberFromList :: [Int] -> Bool
+prop_MemberFromList xs
+  = all (`member` t) abs_xs && all ((`notMember` t) . negate) abs_xs
+  where abs_xs = [abs x | x <- xs, x /= 0]
+        t = fromList abs_xs
+
+{--------------------------------------------------------------------
+  Union
+--------------------------------------------------------------------}
+prop_UnionInsert :: Int -> IntSet -> Bool
+prop_UnionInsert x t
+  = union t (singleton x) == insert x t
+
+prop_UnionAssoc :: IntSet -> IntSet -> IntSet -> Bool
+prop_UnionAssoc t1 t2 t3
+  = union t1 (union t2 t3) == union (union t1 t2) t3
+
+prop_UnionComm :: IntSet -> IntSet -> Bool
+prop_UnionComm t1 t2
+  = (union t1 t2 == union t2 t1)
+
+prop_Diff :: [Int] -> [Int] -> Bool
+prop_Diff xs ys
+  =  toAscList (difference (fromList xs) (fromList ys))
+    == List.sort ((List.\\) (nub xs)  (nub ys))
+
+prop_Int :: [Int] -> [Int] -> Bool
+prop_Int xs ys
+  =  toAscList (intersection (fromList xs) (fromList ys))
+    == List.sort (nub ((List.intersect) (xs)  (ys)))
+
+{--------------------------------------------------------------------
+  Lists
+--------------------------------------------------------------------}
+prop_Ordered
+  = forAll (choose (5,100)) $ \n ->
+    let xs = concat [[i-n,i-n]|i<-[0..2*n :: Int]]
+    in fromAscList xs == fromList xs
+
+prop_List :: [Int] -> Bool
+prop_List xs
+  = (sort (nub xs) == toAscList (fromList xs))
+
+prop_DescList :: [Int] -> Bool
+prop_DescList xs = (reverse (sort (nub xs)) == toDescList (fromList xs))
+
+prop_AscDescList :: [Int] -> Bool
+prop_AscDescList xs = toAscList s == reverse (toDescList s)
+  where s = fromList xs
+
+prop_fromList :: [Int] -> Bool
+prop_fromList xs
+  = case fromList xs of
+      t -> t == fromAscList sort_xs &&
+           t == fromDistinctAscList nub_sort_xs &&
+           t == List.foldr insert empty xs
+  where sort_xs = sort xs
+        nub_sort_xs = List.map List.head $ List.group sort_xs
+
+{--------------------------------------------------------------------
+  Bin invariants
+--------------------------------------------------------------------}
+powersOf2 :: IntSet
+powersOf2 = fromList [2^i | i <- [0..63]]
+
+-- Check the invariant that the mask is a power of 2.
+prop_MaskPow2 :: IntSet -> Bool
+prop_MaskPow2 (Bin _ msk left right) = member msk powersOf2 && prop_MaskPow2 left && prop_MaskPow2 right
+prop_MaskPow2 _ = True
+
+-- Check that the prefix satisfies its invariant.
+prop_Prefix :: IntSet -> Bool
+prop_Prefix s@(Bin prefix msk left right) = all (\elem -> match elem prefix msk) (toList s) && prop_Prefix left && prop_Prefix right
+prop_Prefix _ = True
+
+-- Check that the left elements don't have the mask bit set, and the right
+-- ones do.
+prop_LeftRight :: IntSet -> Bool
+prop_LeftRight (Bin _ msk left right) = and [x .&. msk == 0 | x <- toList left] && and [x .&. msk == msk | x <- toList right]
+prop_LeftRight _ = True
+
+{--------------------------------------------------------------------
+  IntSet operations are like Set operations
+--------------------------------------------------------------------}
+toSet :: IntSet -> Set.Set Int
+toSet = Set.fromList . toList
+
+-- Check that IntSet.isProperSubsetOf is the same as Set.isProperSubsetOf.
+prop_isProperSubsetOf :: IntSet -> IntSet -> Bool
+prop_isProperSubsetOf a b = isProperSubsetOf a b == Set.isProperSubsetOf (toSet a) (toSet b)
+
+-- In the above test, isProperSubsetOf almost always returns False (since a
+-- random set is almost never a subset of another random set).  So this second
+-- test checks the True case.
+prop_isProperSubsetOf2 :: IntSet -> IntSet -> Bool
+prop_isProperSubsetOf2 a b = isProperSubsetOf a c == (a /= c) where
+  c = union a b
+
+prop_isSubsetOf :: IntSet -> IntSet -> Bool
+prop_isSubsetOf a b = isSubsetOf a b == Set.isSubsetOf (toSet a) (toSet b)
+
+prop_isSubsetOf2 :: IntSet -> IntSet -> Bool
+prop_isSubsetOf2 a b = isSubsetOf a (union a b)
+
+prop_size :: IntSet -> Bool
+prop_size s = size s == List.length (toList s)
+
+prop_findMax :: IntSet -> Property
+prop_findMax s = not (null s) ==> findMax s == maximum (toList s)
+
+prop_findMin :: IntSet -> Property
+prop_findMin s = not (null s) ==> findMin s == minimum (toList s)
+
+prop_ord :: IntSet -> IntSet -> Bool
+prop_ord s1 s2 = s1 `compare` s2 == toList s1 `compare` toList s2
+
+prop_readShow :: IntSet -> Bool
+prop_readShow s = s == read (show s)
+
+prop_foldR :: IntSet -> Bool
+prop_foldR s = foldr (:) [] s == toList s
+
+prop_foldR' :: IntSet -> Bool
+prop_foldR' s = foldr' (:) [] s == toList s
+
+prop_foldL :: IntSet -> Bool
+prop_foldL s = foldl (flip (:)) [] s == List.foldl (flip (:)) [] (toList s)
+
+prop_foldL' :: IntSet -> Bool
+prop_foldL' s = foldl' (flip (:)) [] s == List.foldl' (flip (:)) [] (toList s)
+
+prop_map :: IntSet -> Bool
+prop_map s = map id s == s
+
+prop_maxView :: IntSet -> Bool
+prop_maxView s = case maxView s of
+    Nothing -> null s
+    Just (m,s') -> m == maximum (toList s) && s == insert m s' && m `notMember` s'
+
+prop_minView :: IntSet -> Bool
+prop_minView s = case minView s of
+    Nothing -> null s
+    Just (m,s') -> m == minimum (toList s) && s == insert m s' && m `notMember` s'
+
+prop_split :: IntSet -> Int -> Bool
+prop_split s i = case split i s of
+    (s1,s2) -> all (<i) (toList s1) && all (>i) (toList s2) && i `delete` s == union s1 s2
+
+prop_splitMember :: IntSet -> Int -> Bool
+prop_splitMember s i = case splitMember i s of
+    (s1,t,s2) -> all (<i) (toList s1) && all (>i) (toList s2) && t == i `member` s && i `delete` s == union s1 s2
+
+prop_splitRoot :: IntSet -> Bool
+prop_splitRoot s = loop ls && (s == unions ls)
+ where
+  ls = splitRoot s
+  loop [] = True
+  loop (s1:rst) = List.null
+                  [ (x,y) | x <- toList s1
+                          , y <- toList (unions rst)
+                          , x > y ]
+
+prop_partition :: IntSet -> Int -> Bool
+prop_partition s i = case partition odd s of
+    (s1,s2) -> all odd (toList s1) && all even (toList s2) && s == s1 `union` s2
+
+prop_filter :: IntSet -> Int -> Bool
+prop_filter s i = partition odd s == (filter odd s, filter even s)
+
+#if MIN_VERSION_base(4,5,0)
+prop_bitcount :: Int -> Word -> Bool
+prop_bitcount a w = bitcount_orig a w == bitcount_new a w
+  where
+    bitcount_orig a0 x0 = go a0 x0
+      where go a 0 = a
+            go a x = go (a + 1) (x .&. (x-1))
+    bitcount_new a x = a + popCount x
+#endif
diff --git a/tests/map-properties.hs b/tests/map-properties.hs
new file mode 100644
--- /dev/null
+++ b/tests/map-properties.hs
@@ -0,0 +1,1203 @@
+{-# LANGUAGE CPP #-}
+
+#ifdef STRICT
+import Data.Map.Strict as Data.Map
+#else
+import Data.Map.Lazy as Data.Map
+#endif
+
+import Data.Monoid
+import Data.Maybe hiding (mapMaybe)
+import qualified Data.Maybe as Maybe (mapMaybe)
+import Data.Ord
+import Data.Function
+import Prelude hiding (lookup, null, map, filter, foldr, foldl)
+import qualified Prelude (map)
+
+import Data.List (nub,sort)
+import qualified Data.List as List
+import qualified Data.Set
+import Test.Framework
+import Test.Framework.Providers.HUnit
+import Test.Framework.Providers.QuickCheck2
+import Test.HUnit hiding (Test, Testable)
+import Test.QuickCheck
+import Text.Show.Functions ()
+
+default (Int)
+
+main :: IO ()
+main = defaultMain
+         [ testCase "ticket4242" test_ticket4242
+         , testCase "index"      test_index
+         , testCase "size"       test_size
+         , testCase "size2"      test_size2
+         , testCase "member"     test_member
+         , testCase "notMember"  test_notMember
+         , testCase "lookup"     test_lookup
+         , testCase "findWithDefault"     test_findWithDefault
+         , testCase "lookupLT"   test_lookupLT
+         , testCase "lookupGT"   test_lookupGT
+         , testCase "lookupLE"   test_lookupLE
+         , testCase "lookupGE"   test_lookupGE
+         , testCase "empty" test_empty
+         , testCase "mempty" test_mempty
+         , testCase "singleton" test_singleton
+         , testCase "insert" test_insert
+         , testCase "insertWith" test_insertWith
+         , testCase "insertWithKey" test_insertWithKey
+         , testCase "insertLookupWithKey" test_insertLookupWithKey
+         , testCase "delete" test_delete
+         , testCase "adjust" test_adjust
+         , testCase "adjustWithKey" test_adjustWithKey
+         , testCase "update" test_update
+         , testCase "updateWithKey" test_updateWithKey
+         , testCase "updateLookupWithKey" test_updateLookupWithKey
+         , testCase "alter" test_alter
+         , testCase "union" test_union
+         , testCase "mappend" test_mappend
+         , testCase "unionWith" test_unionWith
+         , testCase "unionWithKey" test_unionWithKey
+         , testCase "unions" test_unions
+         , testCase "mconcat" test_mconcat
+         , testCase "unionsWith" test_unionsWith
+         , testCase "difference" test_difference
+         , testCase "differenceWith" test_differenceWith
+         , testCase "differenceWithKey" test_differenceWithKey
+         , testCase "intersection" test_intersection
+         , testCase "intersectionWith" test_intersectionWith
+         , testCase "intersectionWithKey" test_intersectionWithKey
+         , testCase "map" test_map
+         , testCase "mapWithKey" test_mapWithKey
+         , testCase "mapAccum" test_mapAccum
+         , testCase "mapAccumWithKey" test_mapAccumWithKey
+         , testCase "mapAccumRWithKey" test_mapAccumRWithKey
+         , testCase "mapKeys" test_mapKeys
+         , testCase "mapKeysWith" test_mapKeysWith
+         , testCase "mapKeysMonotonic" test_mapKeysMonotonic
+         , testCase "elems" test_elems
+         , testCase "keys" test_keys
+         , testCase "assocs" test_assocs
+         , testCase "keysSet" test_keysSet
+         , testCase "fromSet" test_fromSet
+         , testCase "toList" test_toList
+         , testCase "fromList" test_fromList
+         , testCase "fromListWith" test_fromListWith
+         , testCase "fromListWithKey" test_fromListWithKey
+         , testCase "toAscList" test_toAscList
+         , testCase "toDescList" test_toDescList
+         , testCase "showTree" test_showTree
+         , testCase "showTree'" test_showTree'
+         , testCase "fromAscList" test_fromAscList
+         , testCase "fromAscListWith" test_fromAscListWith
+         , testCase "fromAscListWithKey" test_fromAscListWithKey
+         , testCase "fromDistinctAscList" test_fromDistinctAscList
+         , testCase "filter" test_filter
+         , testCase "filterWithKey" test_filteWithKey
+         , testCase "partition" test_partition
+         , testCase "partitionWithKey" test_partitionWithKey
+         , testCase "mapMaybe" test_mapMaybe
+         , testCase "mapMaybeWithKey" test_mapMaybeWithKey
+         , testCase "mapEither" test_mapEither
+         , testCase "mapEitherWithKey" test_mapEitherWithKey
+         , testCase "split" test_split
+         , testCase "splitLookup" test_splitLookup
+         , testCase "isSubmapOfBy" test_isSubmapOfBy
+         , testCase "isSubmapOf" test_isSubmapOf
+         , testCase "isProperSubmapOfBy" test_isProperSubmapOfBy
+         , testCase "isProperSubmapOf" test_isProperSubmapOf
+         , testCase "lookupIndex" test_lookupIndex
+         , testCase "findIndex" test_findIndex
+         , testCase "elemAt" test_elemAt
+         , testCase "updateAt" test_updateAt
+         , testCase "deleteAt" test_deleteAt
+         , testCase "findMin" test_findMin
+         , testCase "findMax" test_findMax
+         , testCase "deleteMin" test_deleteMin
+         , testCase "deleteMax" test_deleteMax
+         , testCase "deleteFindMin" test_deleteFindMin
+         , testCase "deleteFindMax" test_deleteFindMax
+         , testCase "updateMin" test_updateMin
+         , testCase "updateMax" test_updateMax
+         , testCase "updateMinWithKey" test_updateMinWithKey
+         , testCase "updateMaxWithKey" test_updateMaxWithKey
+         , testCase "minView" test_minView
+         , testCase "maxView" test_maxView
+         , testCase "minViewWithKey" test_minViewWithKey
+         , testCase "maxViewWithKey" test_maxViewWithKey
+         , testCase "valid" test_valid
+         , testProperty "valid"                prop_valid
+         , testProperty "insert to singleton"  prop_singleton
+         , testProperty "insert"               prop_insert
+         , testProperty "insert then lookup"   prop_insertLookup
+         , testProperty "insert then delete"   prop_insertDelete
+         , testProperty "insert then delete2"  prop_insertDelete2
+         , testProperty "delete non member"    prop_deleteNonMember
+         , testProperty "deleteMin"            prop_deleteMin
+         , testProperty "deleteMax"            prop_deleteMax
+         , testProperty "split"                prop_split
+         , testProperty "splitRoot"            prop_splitRoot
+         , testProperty "split then link"      prop_link
+         , testProperty "split then merge"     prop_merge
+         , testProperty "union"                prop_union
+         , testProperty "union model"          prop_unionModel
+         , testProperty "union singleton"      prop_unionSingleton
+         , testProperty "union associative"    prop_unionAssoc
+         , testProperty "union+unionWith"      prop_unionWith
+         , testProperty "unionWith"            prop_unionWith2
+         , testProperty "union sum"            prop_unionSum
+         , testProperty "difference"           prop_difference
+         , testProperty "difference model"     prop_differenceModel
+         , testProperty "intersection"         prop_intersection
+         , testProperty "intersection model"   prop_intersectionModel
+         , testProperty "intersectionWith"     prop_intersectionWith
+         , testProperty "intersectionWithModel" prop_intersectionWithModel
+         , testProperty "intersectionWithKey"  prop_intersectionWithKey
+         , testProperty "intersectionWithKeyModel" prop_intersectionWithKeyModel
+         , testProperty "mergeWithKey model"   prop_mergeWithKeyModel
+         , testProperty "fromAscList"          prop_ordered
+         , testProperty "fromList then toList" prop_list
+         , testProperty "toDescList"           prop_descList
+         , testProperty "toAscList+toDescList" prop_ascDescList
+         , testProperty "fromList"             prop_fromList
+         , testProperty "alter"                prop_alter
+         , testProperty "index"                prop_index
+         , testProperty "null"                 prop_null
+         , testProperty "member"               prop_member
+         , testProperty "notmember"            prop_notmember
+         , testProperty "lookup"               prop_lookup
+         , testProperty "find"                 prop_find
+         , testProperty "findWithDefault"      prop_findWithDefault
+         , testProperty "lookupLT"             prop_lookupLT
+         , testProperty "lookupGT"             prop_lookupGT
+         , testProperty "lookupLE"             prop_lookupLE
+         , testProperty "lookupGE"             prop_lookupGE
+         , testProperty "findIndex"            prop_findIndex
+         , testProperty "lookupIndex"          prop_lookupIndex
+         , testProperty "findMin"              prop_findMin
+         , testProperty "findMax"              prop_findMax
+         , testProperty "deleteMin"            prop_deleteMinModel
+         , testProperty "deleteMax"            prop_deleteMaxModel
+         , testProperty "filter"               prop_filter
+         , testProperty "partition"            prop_partition
+         , testProperty "map"                  prop_map
+         , testProperty "fmap"                 prop_fmap
+         , testProperty "mapkeys"              prop_mapkeys
+         , testProperty "split"                prop_splitModel
+         , testProperty "foldr"                prop_foldr
+         , testProperty "foldr'"               prop_foldr'
+         , testProperty "foldl"                prop_foldl
+         , testProperty "foldl'"               prop_foldl'
+         , testProperty "keysSet"              prop_keysSet
+         , testProperty "fromSet"              prop_fromSet
+         ]
+
+{--------------------------------------------------------------------
+  Arbitrary, reasonably balanced trees
+--------------------------------------------------------------------}
+instance (Enum k,Arbitrary a) => Arbitrary (Map k a) where
+  arbitrary = sized (arbtree 0 maxkey)
+    where maxkey = 10^5
+
+          arbtree :: (Enum k, Arbitrary a) => Int -> Int -> Int -> Gen (Map k a)
+          arbtree lo hi n = do t <- gentree lo hi n
+                               if balanced t then return t else arbtree lo hi n
+            where gentree lo hi n
+                    | n <= 0        = return Tip
+                    | lo >= hi      = return Tip
+                    | otherwise     = do{ x  <- arbitrary
+                                        ; i  <- choose (lo,hi)
+                                        ; m  <- choose (1,70)
+                                        ; let (ml,mr)  | m==(1::Int)= (1,2)
+                                                       | m==2       = (2,1)
+                                                       | m==3       = (1,1)
+                                                       | otherwise  = (2,2)
+                                        ; l  <- gentree lo (i-1) (n `div` ml)
+                                        ; r  <- gentree (i+1) hi (n `div` mr)
+                                        ; return (bin (toEnum i) x l r)
+                                        }
+
+------------------------------------------------------------------------
+
+type UMap = Map Int ()
+type IMap = Map Int Int
+type SMap = Map Int String
+
+----------------------------------------------------------------
+-- Unit tests
+----------------------------------------------------------------
+
+test_ticket4242 :: Assertion
+test_ticket4242 = (valid $ deleteMin $ deleteMin $ fromList [ (i, ()) | i <- [0,2,5,1,6,4,8,9,7,11,10,3] :: [Int] ]) @?= True
+
+----------------------------------------------------------------
+-- Operators
+
+test_index :: Assertion
+test_index = fromList [(5,'a'), (3,'b')] ! 5 @?= 'a'
+
+----------------------------------------------------------------
+-- Query
+
+test_size :: Assertion
+test_size = do
+    null (empty)           @?= True
+    null (singleton 1 'a') @?= False
+
+test_size2 :: Assertion
+test_size2 = do
+    size empty                                   @?= 0
+    size (singleton 1 'a')                       @?= 1
+    size (fromList([(1,'a'), (2,'c'), (3,'b')])) @?= 3
+
+test_member :: Assertion
+test_member = do
+    member 5 (fromList [(5,'a'), (3,'b')]) @?= True
+    member 1 (fromList [(5,'a'), (3,'b')]) @?= False
+
+test_notMember :: Assertion
+test_notMember = do
+    notMember 5 (fromList [(5,'a'), (3,'b')]) @?= False
+    notMember 1 (fromList [(5,'a'), (3,'b')]) @?= True
+
+test_lookup :: Assertion
+test_lookup = do
+    employeeCurrency "John" @?= Just "Euro"
+    employeeCurrency "Pete" @?= Nothing
+  where
+    employeeDept = fromList([("John","Sales"), ("Bob","IT")])
+    deptCountry = fromList([("IT","USA"), ("Sales","France")])
+    countryCurrency = fromList([("USA", "Dollar"), ("France", "Euro")])
+    employeeCurrency :: String -> Maybe String
+    employeeCurrency name = do
+        dept <- lookup name employeeDept
+        country <- lookup dept deptCountry
+        lookup country countryCurrency
+
+test_findWithDefault :: Assertion
+test_findWithDefault = do
+    findWithDefault 'x' 1 (fromList [(5,'a'), (3,'b')]) @?= 'x'
+    findWithDefault 'x' 5 (fromList [(5,'a'), (3,'b')]) @?= 'a'
+
+test_lookupLT :: Assertion
+test_lookupLT = do
+    lookupLT 3 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+    lookupLT 4 (fromList [(3,'a'), (5,'b')]) @?= Just (3, 'a')
+
+test_lookupGT :: Assertion
+test_lookupGT = do
+    lookupGT 4 (fromList [(3,'a'), (5,'b')]) @?= Just (5, 'b')
+    lookupGT 5 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+
+test_lookupLE :: Assertion
+test_lookupLE = do
+    lookupLE 2 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+    lookupLE 4 (fromList [(3,'a'), (5,'b')]) @?= Just (3, 'a')
+    lookupLE 5 (fromList [(3,'a'), (5,'b')]) @?= Just (5, 'b')
+
+test_lookupGE :: Assertion
+test_lookupGE = do
+    lookupGE 3 (fromList [(3,'a'), (5,'b')]) @?= Just (3, 'a')
+    lookupGE 4 (fromList [(3,'a'), (5,'b')]) @?= Just (5, 'b')
+    lookupGE 6 (fromList [(3,'a'), (5,'b')]) @?= Nothing
+
+----------------------------------------------------------------
+-- Construction
+
+test_empty :: Assertion
+test_empty = do
+    (empty :: UMap)  @?= fromList []
+    size empty @?= 0
+
+test_mempty :: Assertion
+test_mempty = do
+    (mempty :: UMap)  @?= fromList []
+    size (mempty :: UMap) @?= 0
+
+test_singleton :: Assertion
+test_singleton = do
+    singleton 1 'a'        @?= fromList [(1, 'a')]
+    size (singleton 1 'a') @?= 1
+
+test_insert :: Assertion
+test_insert = do
+    insert 5 'x' (fromList [(5,'a'), (3,'b')]) @?= fromList [(3, 'b'), (5, 'x')]
+    insert 7 'x' (fromList [(5,'a'), (3,'b')]) @?= fromList [(3, 'b'), (5, 'a'), (7, 'x')]
+    insert 5 'x' empty                         @?= singleton 5 'x'
+
+test_insertWith :: Assertion
+test_insertWith = do
+    insertWith (++) 5 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "xxxa")]
+    insertWith (++) 7 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a"), (7, "xxx")]
+    insertWith (++) 5 "xxx" empty                         @?= singleton 5 "xxx"
+
+test_insertWithKey :: Assertion
+test_insertWithKey = do
+    insertWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "5:xxx|a")]
+    insertWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a"), (7, "xxx")]
+    insertWithKey f 5 "xxx" empty                         @?= singleton 5 "xxx"
+  where
+    f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+
+test_insertLookupWithKey :: Assertion
+test_insertLookupWithKey = do
+    insertLookupWithKey f 5 "xxx" (fromList [(5,"a"), (3,"b")]) @?= (Just "a", fromList [(3, "b"), (5, "5:xxx|a")])
+    insertLookupWithKey f 2 "xxx" (fromList [(5,"a"), (3,"b")]) @?= (Nothing,fromList [(2,"xxx"),(3,"b"),(5,"a")])
+    insertLookupWithKey f 7 "xxx" (fromList [(5,"a"), (3,"b")]) @?= (Nothing,  fromList [(3, "b"), (5, "a"), (7, "xxx")])
+    insertLookupWithKey f 5 "xxx" empty                         @?= (Nothing,  singleton 5 "xxx")
+  where
+    f key new_value old_value = (show key) ++ ":" ++ new_value ++ "|" ++ old_value
+
+----------------------------------------------------------------
+-- Delete/Update
+
+test_delete :: Assertion
+test_delete = do
+    delete 5 (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+    delete 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    delete 5 empty                         @?= (empty :: IMap)
+
+test_adjust :: Assertion
+test_adjust = do
+    adjust ("new " ++) 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "new a")]
+    adjust ("new " ++) 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    adjust ("new " ++) 7 empty                         @?= empty
+
+test_adjustWithKey :: Assertion
+test_adjustWithKey = do
+    adjustWithKey f 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "5:new a")]
+    adjustWithKey f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    adjustWithKey f 7 empty                         @?= empty
+  where
+    f key x = (show key) ++ ":new " ++ x
+
+test_update :: Assertion
+test_update = do
+    update f 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "new a")]
+    update f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    update f 3 (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+  where
+    f x = if x == "a" then Just "new a" else Nothing
+
+test_updateWithKey :: Assertion
+test_updateWithKey = do
+    updateWithKey f 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "5:new a")]
+    updateWithKey f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    updateWithKey f 3 (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+ where
+     f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+
+test_updateLookupWithKey :: Assertion
+test_updateLookupWithKey = do
+    updateLookupWithKey f 5 (fromList [(5,"a"), (3,"b")]) @?= (Just "5:new a", fromList [(3, "b"), (5, "5:new a")])
+    updateLookupWithKey f 7 (fromList [(5,"a"), (3,"b")]) @?= (Nothing,  fromList [(3, "b"), (5, "a")])
+    updateLookupWithKey f 3 (fromList [(5,"a"), (3,"b")]) @?= (Just "b", singleton 5 "a")
+  where
+    f k x = if x == "a" then Just ((show k) ++ ":new a") else Nothing
+
+test_alter :: Assertion
+test_alter = do
+    alter f 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a")]
+    alter f 5 (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+    alter g 7 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "a"), (7, "c")]
+    alter g 5 (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "c")]
+  where
+    f _ = Nothing
+    g _ = Just "c"
+
+----------------------------------------------------------------
+-- Combine
+
+test_union :: Assertion
+test_union = union (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+
+test_mappend :: Assertion
+test_mappend = mappend (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+
+test_unionWith :: Assertion
+test_unionWith = unionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "aA"), (7, "C")]
+
+test_unionWithKey :: Assertion
+test_unionWithKey = unionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= fromList [(3, "b"), (5, "5:a|A"), (7, "C")]
+  where
+    f key left_value right_value = (show key) ++ ":" ++ left_value ++ "|" ++ right_value
+
+test_unions :: Assertion
+test_unions = do
+    unions [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+        @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+    unions [(fromList [(5, "A3"), (3, "B3")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "a"), (3, "b")])]
+        @?= fromList [(3, "B3"), (5, "A3"), (7, "C")]
+
+test_mconcat :: Assertion
+test_mconcat = do
+    mconcat [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+        @?= fromList [(3, "b"), (5, "a"), (7, "C")]
+    mconcat [(fromList [(5, "A3"), (3, "B3")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "a"), (3, "b")])]
+        @?= fromList [(3, "B3"), (5, "A3"), (7, "C")]
+
+test_unionsWith :: Assertion
+test_unionsWith = unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
+     @?= fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
+
+test_difference :: Assertion
+test_difference = difference (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 3 "b"
+
+test_differenceWith :: Assertion
+test_differenceWith = differenceWith f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (7, "C")])
+     @?= singleton 3 "b:B"
+ where
+   f al ar = if al== "b" then Just (al ++ ":" ++ ar) else Nothing
+
+test_differenceWithKey :: Assertion
+test_differenceWithKey = differenceWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (3, "B"), (10, "C")])
+     @?= singleton 3 "3:b|B"
+  where
+    f k al ar = if al == "b" then Just ((show k) ++ ":" ++ al ++ "|" ++ ar) else Nothing
+
+test_intersection :: Assertion
+test_intersection = intersection (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 5 "a"
+
+
+test_intersectionWith :: Assertion
+test_intersectionWith = intersectionWith (++) (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 5 "aA"
+
+test_intersectionWithKey :: Assertion
+test_intersectionWithKey = intersectionWithKey f (fromList [(5, "a"), (3, "b")]) (fromList [(5, "A"), (7, "C")]) @?= singleton 5 "5:a|A"
+  where
+    f k al ar = (show k) ++ ":" ++ al ++ "|" ++ ar
+
+----------------------------------------------------------------
+-- Traversal
+
+test_map :: Assertion
+test_map = map (++ "x") (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "bx"), (5, "ax")]
+
+test_mapWithKey :: Assertion
+test_mapWithKey = mapWithKey f (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "3:b"), (5, "5:a")]
+  where
+    f key x = (show key) ++ ":" ++ x
+
+test_mapAccum :: Assertion
+test_mapAccum = mapAccum f "Everything: " (fromList [(5,"a"), (3,"b")]) @?= ("Everything: ba", fromList [(3, "bX"), (5, "aX")])
+  where
+    f a b = (a ++ b, b ++ "X")
+
+test_mapAccumWithKey :: Assertion
+test_mapAccumWithKey = mapAccumWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) @?= ("Everything: 3-b 5-a", fromList [(3, "bX"), (5, "aX")])
+  where
+    f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+
+test_mapAccumRWithKey :: Assertion
+test_mapAccumRWithKey = mapAccumRWithKey f "Everything:" (fromList [(5,"a"), (3,"b")]) @?= ("Everything: 5-a 3-b", fromList [(3, "bX"), (5, "aX")])
+  where
+    f a k b = (a ++ " " ++ (show k) ++ "-" ++ b, b ++ "X")
+
+test_mapKeys :: Assertion
+test_mapKeys = do
+    mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])                        @?= fromList [(4, "b"), (6, "a")]
+    mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 1 "c"
+    mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 3 "c"
+
+test_mapKeysWith :: Assertion
+test_mapKeysWith = do
+    mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 1 "cdab"
+    mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) @?= singleton 3 "cdab"
+
+test_mapKeysMonotonic :: Assertion
+test_mapKeysMonotonic = do
+    mapKeysMonotonic (+ 1) (fromList [(5,"a"), (3,"b")])          @?= fromList [(4, "b"), (6, "a")]
+    mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")]) @?= fromList [(6, "b"), (10, "a")]
+    valid (mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")])) @?= True
+    valid (mapKeysMonotonic (\ _ -> 1)     (fromList [(5,"a"), (3,"b")])) @?= False
+
+----------------------------------------------------------------
+-- Conversion
+
+test_elems :: Assertion
+test_elems = do
+    elems (fromList [(5,"a"), (3,"b")]) @?= ["b","a"]
+    elems (empty :: UMap) @?= []
+
+test_keys :: Assertion
+test_keys = do
+    keys (fromList [(5,"a"), (3,"b")]) @?= [3,5]
+    keys (empty :: UMap) @?= []
+
+test_assocs :: Assertion
+test_assocs = do
+    assocs (fromList [(5,"a"), (3,"b")]) @?= [(3,"b"), (5,"a")]
+    assocs (empty :: UMap) @?= []
+
+test_keysSet :: Assertion
+test_keysSet = do
+    keysSet (fromList [(5,"a"), (3,"b")]) @?= Data.Set.fromList [3,5]
+    keysSet (empty :: UMap) @?= Data.Set.empty
+
+test_fromSet :: Assertion
+test_fromSet = do
+   fromSet (\k -> replicate k 'a') (Data.Set.fromList [3, 5]) @?= fromList [(5,"aaaaa"), (3,"aaa")]
+   fromSet undefined Data.Set.empty @?= (empty :: IMap)
+
+----------------------------------------------------------------
+-- Lists
+
+test_toList :: Assertion
+test_toList = do
+    toList (fromList [(5,"a"), (3,"b")]) @?= [(3,"b"), (5,"a")]
+    toList (empty :: SMap) @?= []
+
+test_fromList :: Assertion
+test_fromList = do
+    fromList [] @?= (empty :: SMap)
+    fromList [(5,"a"), (3,"b"), (5, "c")] @?= fromList [(5,"c"), (3,"b")]
+    fromList [(5,"c"), (3,"b"), (5, "a")] @?= fromList [(5,"a"), (3,"b")]
+
+test_fromListWith :: Assertion
+test_fromListWith = do
+    fromListWith (++) [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] @?= fromList [(3, "ab"), (5, "aba")]
+    fromListWith (++) [] @?= (empty :: SMap)
+
+test_fromListWithKey :: Assertion
+test_fromListWithKey = do
+    fromListWithKey f [(5,"a"), (5,"b"), (3,"b"), (3,"a"), (5,"a")] @?= fromList [(3, "3ab"), (5, "5a5ba")]
+    fromListWithKey f [] @?= (empty :: SMap)
+  where
+    f k a1 a2 = (show k) ++ a1 ++ a2
+
+----------------------------------------------------------------
+-- Ordered lists
+
+test_toAscList :: Assertion
+test_toAscList = toAscList (fromList [(5,"a"), (3,"b")]) @?= [(3,"b"), (5,"a")]
+
+test_toDescList :: Assertion
+test_toDescList = toDescList (fromList [(5,"a"), (3,"b")]) @?= [(5,"a"), (3,"b")]
+
+test_showTree :: Assertion
+test_showTree =
+       (let t = fromDistinctAscList [(x,()) | x <- [1..5]]
+        in showTree t) @?= "4:=()\n+--2:=()\n|  +--1:=()\n|  +--3:=()\n+--5:=()\n"
+
+test_showTree' :: Assertion
+test_showTree' =
+       (let t = fromDistinctAscList [(x,()) | x <- [1..5]]
+        in s t ) @?= "+--5:=()\n|\n4:=()\n|\n|  +--3:=()\n|  |\n+--2:=()\n   |\n   +--1:=()\n"
+   where
+    showElem k x  = show k ++ ":=" ++ show x
+
+    s = showTreeWith showElem False True
+
+
+test_fromAscList :: Assertion
+test_fromAscList = do
+    fromAscList [(3,"b"), (5,"a")]          @?= fromList [(3, "b"), (5, "a")]
+    fromAscList [(3,"b"), (5,"a"), (5,"b")] @?= fromList [(3, "b"), (5, "b")]
+    valid (fromAscList [(3,"b"), (5,"a"), (5,"b")]) @?= True
+    valid (fromAscList [(5,"a"), (3,"b"), (5,"b")]) @?= False
+
+test_fromAscListWith :: Assertion
+test_fromAscListWith = do
+    fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")] @?= fromList [(3, "b"), (5, "ba")]
+    valid (fromAscListWith (++) [(3,"b"), (5,"a"), (5,"b")]) @?= True
+    valid (fromAscListWith (++) [(5,"a"), (3,"b"), (5,"b")]) @?= False
+
+test_fromAscListWithKey :: Assertion
+test_fromAscListWithKey = do
+    fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")] @?= fromList [(3, "b"), (5, "5:b5:ba")]
+    valid (fromAscListWithKey f [(3,"b"), (5,"a"), (5,"b"), (5,"b")]) @?= True
+    valid (fromAscListWithKey f [(5,"a"), (3,"b"), (5,"b"), (5,"b")]) @?= False
+  where
+    f k a1 a2 = (show k) ++ ":" ++ a1 ++ a2
+
+test_fromDistinctAscList :: Assertion
+test_fromDistinctAscList = do
+    fromDistinctAscList [(3,"b"), (5,"a")] @?= fromList [(3, "b"), (5, "a")]
+    valid (fromDistinctAscList [(3,"b"), (5,"a")])          @?= True
+    valid (fromDistinctAscList [(3,"b"), (5,"a"), (5,"b")]) @?= False
+
+----------------------------------------------------------------
+-- Filter
+
+test_filter :: Assertion
+test_filter = do
+    filter (> "a") (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+    filter (> "x") (fromList [(5,"a"), (3,"b")]) @?= empty
+    filter (< "a") (fromList [(5,"a"), (3,"b")]) @?= empty
+
+test_filteWithKey :: Assertion
+test_filteWithKey = filterWithKey (\k _ -> k > 4) (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+
+test_partition :: Assertion
+test_partition = do
+    partition (> "a") (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", singleton 5 "a")
+    partition (< "x") (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3, "b"), (5, "a")], empty)
+    partition (> "x") (fromList [(5,"a"), (3,"b")]) @?= (empty, fromList [(3, "b"), (5, "a")])
+
+test_partitionWithKey :: Assertion
+test_partitionWithKey = do
+    partitionWithKey (\ k _ -> k > 3) (fromList [(5,"a"), (3,"b")]) @?= (singleton 5 "a", singleton 3 "b")
+    partitionWithKey (\ k _ -> k < 7) (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3, "b"), (5, "a")], empty)
+    partitionWithKey (\ k _ -> k > 7) (fromList [(5,"a"), (3,"b")]) @?= (empty, fromList [(3, "b"), (5, "a")])
+
+test_mapMaybe :: Assertion
+test_mapMaybe = mapMaybe f (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "new a"
+  where
+    f x = if x == "a" then Just "new a" else Nothing
+
+test_mapMaybeWithKey :: Assertion
+test_mapMaybeWithKey = mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "key : 3"
+  where
+    f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
+
+test_mapEither :: Assertion
+test_mapEither = do
+    mapEither f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+        @?= (fromList [(3,"b"), (5,"a")], fromList [(1,"x"), (7,"z")])
+    mapEither (\ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+        @?= ((empty :: SMap), fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+ where
+   f a = if a < "c" then Left a else Right a
+
+test_mapEitherWithKey :: Assertion
+test_mapEitherWithKey = do
+    mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+     @?= (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])
+    mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
+     @?= ((empty :: SMap), fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])
+  where
+    f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
+
+test_split :: Assertion
+test_split = do
+    split 2 (fromList [(5,"a"), (3,"b")]) @?= (empty, fromList [(3,"b"), (5,"a")])
+    split 3 (fromList [(5,"a"), (3,"b")]) @?= (empty, singleton 5 "a")
+    split 4 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", singleton 5 "a")
+    split 5 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", empty)
+    split 6 (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3,"b"), (5,"a")], empty)
+
+test_splitLookup :: Assertion
+test_splitLookup = do
+    splitLookup 2 (fromList [(5,"a"), (3,"b")]) @?= (empty, Nothing, fromList [(3,"b"), (5,"a")])
+    splitLookup 3 (fromList [(5,"a"), (3,"b")]) @?= (empty, Just "b", singleton 5 "a")
+    splitLookup 4 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", Nothing, singleton 5 "a")
+    splitLookup 5 (fromList [(5,"a"), (3,"b")]) @?= (singleton 3 "b", Just "a", empty)
+    splitLookup 6 (fromList [(5,"a"), (3,"b")]) @?= (fromList [(3,"b"), (5,"a")], Nothing, empty)
+
+----------------------------------------------------------------
+-- Submap
+
+test_isSubmapOfBy :: Assertion
+test_isSubmapOfBy = do
+    isSubmapOfBy (==) (fromList [('a',1)]) (fromList [('a',1),('b',2)]) @?= True
+    isSubmapOfBy (<=) (fromList [('a',1)]) (fromList [('a',1),('b',2)]) @?= True
+    isSubmapOfBy (==) (fromList [('a',1),('b',2)]) (fromList [('a',1),('b',2)]) @?= True
+    isSubmapOfBy (==) (fromList [('a',2)]) (fromList [('a',1),('b',2)]) @?= False
+    isSubmapOfBy (<)  (fromList [('a',1)]) (fromList [('a',1),('b',2)]) @?= False
+    isSubmapOfBy (==) (fromList [('a',1),('b',2)]) (fromList [('a',1)]) @?= False
+
+test_isSubmapOf :: Assertion
+test_isSubmapOf = do
+    isSubmapOf (fromList [('a',1)]) (fromList [('a',1),('b',2)]) @?= True
+    isSubmapOf (fromList [('a',1),('b',2)]) (fromList [('a',1),('b',2)]) @?= True
+    isSubmapOf (fromList [('a',2)]) (fromList [('a',1),('b',2)]) @?= False
+    isSubmapOf (fromList [('a',1),('b',2)]) (fromList [('a',1)]) @?= False
+
+test_isProperSubmapOfBy :: Assertion
+test_isProperSubmapOfBy = do
+    isProperSubmapOfBy (==) (fromList [(1,1)]) (fromList [(1,1),(2,2)]) @?= True
+    isProperSubmapOfBy (<=) (fromList [(1,1)]) (fromList [(1,1),(2,2)]) @?= True
+    isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)]) @?= False
+    isProperSubmapOfBy (==) (fromList [(1,1),(2,2)]) (fromList [(1,1)]) @?= False
+    isProperSubmapOfBy (<)  (fromList [(1,1)])       (fromList [(1,1),(2,2)]) @?= False
+
+test_isProperSubmapOf :: Assertion
+test_isProperSubmapOf = do
+    isProperSubmapOf (fromList [(1,1)]) (fromList [(1,1),(2,2)]) @?= True
+    isProperSubmapOf (fromList [(1,1),(2,2)]) (fromList [(1,1),(2,2)]) @?= False
+    isProperSubmapOf (fromList [(1,1),(2,2)]) (fromList [(1,1)]) @?= False
+
+----------------------------------------------------------------
+-- Indexed
+
+test_lookupIndex :: Assertion
+test_lookupIndex = do
+    isJust (lookupIndex 2 (fromList [(5,"a"), (3,"b")]))   @?= False
+    fromJust (lookupIndex 3 (fromList [(5,"a"), (3,"b")])) @?= 0
+    fromJust (lookupIndex 5 (fromList [(5,"a"), (3,"b")])) @?= 1
+    isJust (lookupIndex 6 (fromList [(5,"a"), (3,"b")]))   @?= False
+
+test_findIndex :: Assertion
+test_findIndex = do
+    findIndex 3 (fromList [(5,"a"), (3,"b")]) @?= 0
+    findIndex 5 (fromList [(5,"a"), (3,"b")]) @?= 1
+
+test_elemAt :: Assertion
+test_elemAt = do
+    elemAt 0 (fromList [(5,"a"), (3,"b")]) @?= (3,"b")
+    elemAt 1 (fromList [(5,"a"), (3,"b")]) @?= (5, "a")
+
+test_updateAt :: Assertion
+test_updateAt = do
+    updateAt (\ _ _ -> Just "x") 0    (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "x"), (5, "a")]
+    updateAt (\ _ _ -> Just "x") 1    (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "x")]
+    updateAt (\_ _  -> Nothing)  0    (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+    updateAt (\_ _  -> Nothing)  1    (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+--    updateAt (\_ _  -> Nothing)  7    (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+
+test_deleteAt :: Assertion
+test_deleteAt = do
+    deleteAt 0  (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+    deleteAt 1  (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+
+----------------------------------------------------------------
+-- Min/Max
+
+test_findMin :: Assertion
+test_findMin = findMin (fromList [(5,"a"), (3,"b")]) @?= (3,"b")
+
+test_findMax :: Assertion
+test_findMax = findMax (fromList [(5,"a"), (3,"b")]) @?= (5,"a")
+
+test_deleteMin :: Assertion
+test_deleteMin = do
+    deleteMin (fromList [(5,"a"), (3,"b"), (7,"c")]) @?= fromList [(5,"a"), (7,"c")]
+    deleteMin (empty :: SMap) @?= empty
+
+test_deleteMax :: Assertion
+test_deleteMax = do
+    deleteMax (fromList [(5,"a"), (3,"b"), (7,"c")]) @?= fromList [(3,"b"), (5,"a")]
+    deleteMax (empty :: SMap) @?= empty
+
+test_deleteFindMin :: Assertion
+test_deleteFindMin = deleteFindMin (fromList [(5,"a"), (3,"b"), (10,"c")]) @?= ((3,"b"), fromList[(5,"a"), (10,"c")])
+
+test_deleteFindMax :: Assertion
+test_deleteFindMax = deleteFindMax (fromList [(5,"a"), (3,"b"), (10,"c")]) @?= ((10,"c"), fromList [(3,"b"), (5,"a")])
+
+test_updateMin :: Assertion
+test_updateMin = do
+    updateMin (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "Xb"), (5, "a")]
+    updateMin (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+
+test_updateMax :: Assertion
+test_updateMax = do
+    updateMax (\ a -> Just ("X" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3, "b"), (5, "Xa")]
+    updateMax (\ _ -> Nothing)         (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+
+test_updateMinWithKey :: Assertion
+test_updateMinWithKey = do
+    updateMinWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3,"3:b"), (5,"a")]
+    updateMinWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) @?= singleton 5 "a"
+
+test_updateMaxWithKey :: Assertion
+test_updateMaxWithKey = do
+    updateMaxWithKey (\ k a -> Just ((show k) ++ ":" ++ a)) (fromList [(5,"a"), (3,"b")]) @?= fromList [(3,"b"), (5,"5:a")]
+    updateMaxWithKey (\ _ _ -> Nothing)                     (fromList [(5,"a"), (3,"b")]) @?= singleton 3 "b"
+
+test_minView :: Assertion
+test_minView = do
+    minView (fromList [(5,"a"), (3,"b")]) @?= Just ("b", singleton 5 "a")
+    minView (empty :: SMap) @?= Nothing
+
+test_maxView :: Assertion
+test_maxView = do
+    maxView (fromList [(5,"a"), (3,"b")]) @?= Just ("a", singleton 3 "b")
+    maxView (empty :: SMap) @?= Nothing
+
+test_minViewWithKey :: Assertion
+test_minViewWithKey = do
+    minViewWithKey (fromList [(5,"a"), (3,"b")]) @?= Just ((3,"b"), singleton 5 "a")
+    minViewWithKey (empty :: SMap) @?= Nothing
+
+test_maxViewWithKey :: Assertion
+test_maxViewWithKey = do
+    maxViewWithKey (fromList [(5,"a"), (3,"b")]) @?= Just ((5,"a"), singleton 3 "b")
+    maxViewWithKey (empty :: SMap) @?= Nothing
+
+----------------------------------------------------------------
+-- Debug
+
+test_valid :: Assertion
+test_valid = do
+    valid (fromAscList [(3,"b"), (5,"a")]) @?= True
+    valid (fromAscList [(5,"a"), (3,"b")]) @?= False
+
+----------------------------------------------------------------
+-- QuickCheck
+----------------------------------------------------------------
+
+prop_valid :: UMap -> Bool
+prop_valid t = valid t
+
+prop_singleton :: Int -> Int -> Bool
+prop_singleton k x = insert k x empty == singleton k x
+
+prop_insert :: Int -> UMap -> Bool
+prop_insert k t = valid $ insert k () t
+
+prop_insertLookup :: Int -> UMap -> Bool
+prop_insertLookup k t = lookup k (insert k () t) /= Nothing
+
+prop_insertDelete :: Int -> UMap -> Bool
+prop_insertDelete k t = valid $ delete k (insert k () t)
+
+prop_insertDelete2 :: Int -> UMap -> Property
+prop_insertDelete2 k t = (lookup k t == Nothing) ==> (delete k (insert k () t) == t)
+
+prop_deleteNonMember :: Int -> UMap -> Property
+prop_deleteNonMember k t = (lookup k t == Nothing) ==> (delete k t == t)
+
+prop_deleteMin :: UMap -> Bool
+prop_deleteMin t = valid $ deleteMin $ deleteMin t
+
+prop_deleteMax :: UMap -> Bool
+prop_deleteMax t = valid $ deleteMax $ deleteMax t
+
+----------------------------------------------------------------
+
+prop_split :: Int -> UMap -> Bool
+prop_split k t = let (r,l) = split k t
+                 in (valid r, valid l) == (True, True)
+
+prop_splitRoot :: UMap -> Bool
+prop_splitRoot s = loop ls && (s == unions ls)
+ where
+  ls = splitRoot s
+  loop [] = True
+  loop (s1:rst) = List.null
+                  [ (x,y) | x <- toList s1
+                          , y <- toList (unions rst)
+                          , x > y ]
+
+prop_link :: Int -> UMap -> Bool
+prop_link k t = let (l,r) = split k t
+                in valid (link k () l r)
+
+prop_merge :: Int -> UMap -> Bool
+prop_merge k t = let (l,r) = split k t
+                 in valid (merge l r)
+
+----------------------------------------------------------------
+
+prop_union :: UMap -> UMap -> Bool
+prop_union t1 t2 = valid (union t1 t2)
+
+prop_unionModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_unionModel xs ys
+  = sort (keys (union (fromList xs) (fromList ys)))
+    == sort (nub (Prelude.map fst xs ++ Prelude.map fst ys))
+
+prop_unionSingleton :: IMap -> Int -> Int -> Bool
+prop_unionSingleton t k x = union (singleton k x) t == insert k x t
+
+prop_unionAssoc :: IMap -> IMap -> IMap -> Bool
+prop_unionAssoc t1 t2 t3 = union t1 (union t2 t3) == union (union t1 t2) t3
+
+prop_unionWith :: IMap -> IMap -> Bool
+prop_unionWith t1 t2 = (union t1 t2 == unionWith (\_ y -> y) t2 t1)
+
+prop_unionWith2 :: IMap -> IMap -> Bool
+prop_unionWith2 t1 t2 = valid (unionWithKey (\_ x y -> x+y) t1 t2)
+
+prop_unionSum :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_unionSum xs ys
+  = sum (elems (unionWith (+) (fromListWith (+) xs) (fromListWith (+) ys)))
+    == (sum (Prelude.map snd xs) + sum (Prelude.map snd ys))
+
+prop_difference :: IMap -> IMap -> Bool
+prop_difference t1 t2 = valid (difference t1 t2)
+
+prop_differenceModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_differenceModel xs ys
+  = sort (keys (difference (fromListWith (+) xs) (fromListWith (+) ys)))
+    == sort ((List.\\) (nub (Prelude.map fst xs)) (nub (Prelude.map fst ys)))
+
+prop_intersection :: IMap -> IMap -> Bool
+prop_intersection t1 t2 = valid (intersection t1 t2)
+
+prop_intersectionModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_intersectionModel xs ys
+  = sort (keys (intersection (fromListWith (+) xs) (fromListWith (+) ys)))
+    == sort (nub ((List.intersect) (Prelude.map fst xs) (Prelude.map fst ys)))
+
+prop_intersectionWith :: (Int -> Int -> Maybe Int) -> IMap -> IMap -> Bool
+prop_intersectionWith f t1 t2 = valid (intersectionWith f t1 t2)
+
+prop_intersectionWithModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_intersectionWithModel xs ys
+  = toList (intersectionWith f (fromList xs') (fromList ys'))
+    == [(kx, f vx vy) | (kx, vx) <- List.sort xs', (ky, vy) <- ys', kx == ky]
+    where xs' = List.nubBy ((==) `on` fst) xs
+          ys' = List.nubBy ((==) `on` fst) ys
+          f l r = l + 2 * r
+
+prop_intersectionWithKey :: (Int -> Int -> Int -> Maybe Int) -> IMap -> IMap -> Bool
+prop_intersectionWithKey f t1 t2 = valid (intersectionWithKey f t1 t2)
+
+prop_intersectionWithKeyModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_intersectionWithKeyModel xs ys
+  = toList (intersectionWithKey f (fromList xs') (fromList ys'))
+    == [(kx, f kx vx vy) | (kx, vx) <- List.sort xs', (ky, vy) <- ys', kx == ky]
+    where xs' = List.nubBy ((==) `on` fst) xs
+          ys' = List.nubBy ((==) `on` fst) ys
+          f k l r = k + 2 * l + 3 * r
+
+prop_mergeWithKeyModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
+prop_mergeWithKeyModel xs ys
+  = and [ testMergeWithKey f keep_x keep_y
+        | f <- [ \_k x1  _x2 -> Just x1
+               , \_k _x1 x2  -> Just x2
+               , \_k _x1 _x2 -> Nothing
+               , \k  x1  x2  -> if k `mod` 2 == 0 then Nothing else Just (2 * x1 + 3 * x2)
+               ]
+        , keep_x <- [ True, False ]
+        , keep_y <- [ True, False ]
+        ]
+
+    where xs' = List.nubBy ((==) `on` fst) xs
+          ys' = List.nubBy ((==) `on` fst) ys
+
+          xm = fromList xs'
+          ym = fromList ys'
+
+          testMergeWithKey f keep_x keep_y
+            = toList (mergeWithKey f (keep keep_x) (keep keep_y) xm ym) == emulateMergeWithKey f keep_x keep_y
+              where keep False _ = empty
+                    keep True  m = m
+
+                    emulateMergeWithKey f keep_x keep_y
+                      = Maybe.mapMaybe combine (sort $ List.union (List.map fst xs') (List.map fst ys'))
+                        where combine k = case (List.lookup k xs', List.lookup k ys') of
+                                            (Nothing, Just y) -> if keep_y then Just (k, y) else Nothing
+                                            (Just x, Nothing) -> if keep_x then Just (k, x) else Nothing
+                                            (Just x, Just y) -> (\v -> (k, v)) `fmap` f k x y
+
+          -- We prevent inlining testMergeWithKey to disable the SpecConstr
+          -- optimalization. There are too many call patterns here so several
+          -- warnings are issued if testMergeWithKey gets inlined.
+          {-# NOINLINE testMergeWithKey #-}
+
+----------------------------------------------------------------
+
+prop_ordered :: Property
+prop_ordered
+  = forAll (choose (5,100)) $ \n ->
+    let xs = [(x,()) | x <- [0..n::Int]]
+    in fromAscList xs == fromList xs
+
+prop_list :: [Int] -> Bool
+prop_list xs = (sort (nub xs) == [x | (x,()) <- toList (fromList [(x,()) | x <- xs])])
+
+prop_descList :: [Int] -> Bool
+prop_descList xs = (reverse (sort (nub xs)) == [x | (x,()) <- toDescList (fromList [(x,()) | x <- xs])])
+
+prop_ascDescList :: [Int] -> Bool
+prop_ascDescList xs = toAscList m == reverse (toDescList m)
+  where m = fromList $ zip xs $ repeat ()
+
+prop_fromList :: [Int] -> Bool
+prop_fromList xs
+  = case fromList (zip xs xs) of
+      t -> t == fromAscList (zip sort_xs sort_xs) &&
+           t == fromDistinctAscList (zip nub_sort_xs nub_sort_xs) &&
+           t == List.foldr (uncurry insert) empty (zip xs xs)
+  where sort_xs = sort xs
+        nub_sort_xs = List.map List.head $ List.group sort_xs
+
+----------------------------------------------------------------
+
+prop_alter :: UMap -> Int -> Bool
+prop_alter t k = balanced t' && case lookup k t of
+    Just _  -> (size t - 1) == size t' && lookup k t' == Nothing
+    Nothing -> (size t + 1) == size t' && lookup k t' /= Nothing
+  where
+    t' = alter f k t
+    f Nothing   = Just ()
+    f (Just ()) = Nothing
+
+------------------------------------------------------------------------
+-- Compare against the list model (after nub on keys)
+
+prop_index :: [Int] -> Property
+prop_index xs = length xs > 0 ==>
+  let m  = fromList (zip xs xs)
+  in  xs == [ m ! i | i <- xs ]
+
+prop_null :: IMap -> Bool
+prop_null m = null m == (size m == 0)
+
+prop_member :: [Int] -> Int -> Bool
+prop_member xs n =
+  let m  = fromList (zip xs xs)
+  in all (\k -> k `member` m == (k `elem` xs)) (n : xs)
+
+prop_notmember :: [Int] -> Int -> Bool
+prop_notmember xs n =
+  let m  = fromList (zip xs xs)
+  in all (\k -> k `notMember` m == (k `notElem` xs)) (n : xs)
+
+prop_lookup :: [(Int, Int)] -> Int -> Bool
+prop_lookup xs n =
+  let xs' = List.nubBy ((==) `on` fst) xs
+      m = fromList xs'
+  in all (\k -> lookup k m == List.lookup k xs') (n : List.map fst xs')
+
+prop_find :: [(Int, Int)] -> Bool
+prop_find xs =
+  let xs' = List.nubBy ((==) `on` fst) xs
+      m = fromList xs'
+  in all (\(k, v) -> m ! k == v) xs'
+
+prop_findWithDefault :: [(Int, Int)] -> Int -> Int -> Bool
+prop_findWithDefault xs n x =
+  let xs' = List.nubBy ((==) `on` fst) xs
+      m = fromList xs'
+  in all (\k -> findWithDefault x k m == maybe x id (List.lookup k xs')) (n : List.map fst xs')
+
+test_lookupSomething :: (Int -> Map Int Int -> Maybe (Int, Int)) -> (Int -> Int -> Bool) -> [(Int, Int)] -> Bool
+test_lookupSomething lookup' cmp xs =
+  let odd_sorted_xs = filter_odd $ sort $ List.nubBy ((==) `on` fst) xs
+      t = fromList odd_sorted_xs
+      test k = case List.filter ((`cmp` k) . fst) odd_sorted_xs of
+                 []             -> lookup' k t == Nothing
+                 cs | 0 `cmp` 1 -> lookup' k t == Just (last cs) -- we want largest such element
+                    | otherwise -> lookup' k t == Just (head cs) -- we want smallest such element
+  in all test (List.map fst xs)
+
+  where filter_odd [] = []
+        filter_odd [_] = []
+        filter_odd (_ : o : xs) = o : filter_odd xs
+
+prop_lookupLT :: [(Int, Int)] -> Bool
+prop_lookupLT = test_lookupSomething lookupLT (<)
+
+prop_lookupGT :: [(Int, Int)] -> Bool
+prop_lookupGT = test_lookupSomething lookupGT (>)
+
+prop_lookupLE :: [(Int, Int)] -> Bool
+prop_lookupLE = test_lookupSomething lookupLE (<=)
+
+prop_lookupGE :: [(Int, Int)] -> Bool
+prop_lookupGE = test_lookupSomething lookupGE (>=)
+
+prop_findIndex :: [(Int, Int)] -> Property
+prop_findIndex ys = length ys > 0 ==>
+  let m = fromList ys
+  in  findIndex (fst (head ys)) m `seq` True
+
+prop_lookupIndex :: [(Int, Int)] -> Property
+prop_lookupIndex ys = length ys > 0 ==>
+  let m = fromList ys
+  in  isJust (lookupIndex (fst (head ys)) m)
+
+prop_findMin :: [(Int, Int)] -> Property
+prop_findMin ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  findMin m == List.minimumBy (comparing fst) xs
+
+prop_findMax :: [(Int, Int)] -> Property
+prop_findMax ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  findMax m == List.maximumBy (comparing fst) xs
+
+prop_deleteMinModel :: [(Int, Int)] -> Property
+prop_deleteMinModel ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  toAscList (deleteMin m) == tail (sort xs)
+
+prop_deleteMaxModel :: [(Int, Int)] -> Property
+prop_deleteMaxModel ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  toAscList (deleteMax m) == init (sort xs)
+
+prop_filter :: (Int -> Bool) -> [(Int, Int)] -> Property
+prop_filter p ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  filter p m == fromList (List.filter (p . snd) xs)
+
+prop_partition :: (Int -> Bool) -> [(Int, Int)] -> Property
+prop_partition p ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  partition p m == let (a,b) = (List.partition (p . snd) xs) in (fromList a, fromList b)
+
+prop_map :: (Int -> Int) -> [(Int, Int)] -> Property
+prop_map f ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  map f m == fromList [ (a, f b) | (a,b) <- xs ]
+
+prop_fmap :: (Int -> Int) -> [(Int, Int)] -> Property
+prop_fmap f ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  fmap f m == fromList [ (a, f b) | (a,b) <- xs ]
+
+prop_mapkeys :: (Int -> Int) -> [(Int, Int)] -> Property
+prop_mapkeys f ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  mapKeys f m == (fromList $ List.nubBy ((==) `on` fst) $ reverse [ (f a, b) | (a,b) <- sort xs])
+
+prop_splitModel :: Int -> [(Int, Int)] -> Property
+prop_splitModel n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      (l, r) = split n $ fromList xs
+  in  toAscList l == sort [(k, v) | (k,v) <- xs, k < n] &&
+      toAscList r == sort [(k, v) | (k,v) <- xs, k > n]
+
+prop_foldr :: Int -> [(Int, Int)] -> Property
+prop_foldr n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldr (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldr (:) [] m == List.map snd (List.sort xs) &&
+      foldrWithKey (\_ a b -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldrWithKey (\k _ b -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldrWithKey (\k x xs -> (k,x):xs) [] m == List.sort xs
+
+
+prop_foldr' :: Int -> [(Int, Int)] -> Property
+prop_foldr' n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldr' (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldr' (:) [] m == List.map snd (List.sort xs) &&
+      foldrWithKey' (\_ a b -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldrWithKey' (\k _ b -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldrWithKey' (\k x xs -> (k,x):xs) [] m == List.sort xs
+
+prop_foldl :: Int -> [(Int, Int)] -> Property
+prop_foldl n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldl (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldl (flip (:)) [] m == reverse (List.map snd (List.sort xs)) &&
+      foldlWithKey (\b _ a -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldlWithKey (\b k _ -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldlWithKey (\xs k x -> (k,x):xs) [] m == reverse (List.sort xs)
+
+prop_foldl' :: Int -> [(Int, Int)] -> Property
+prop_foldl' n ys = length ys > 0 ==>
+  let xs = List.nubBy ((==) `on` fst) ys
+      m  = fromList xs
+  in  foldl' (+) n m == List.foldr (+) n (List.map snd xs) &&
+      foldl' (flip (:)) [] m == reverse (List.map snd (List.sort xs)) &&
+      foldlWithKey' (\b _ a -> a + b) n m == List.foldr (+) n (List.map snd xs) &&
+      foldlWithKey' (\b k _ -> k + b) n m == List.foldr (+) n (List.map fst xs) &&
+      foldlWithKey' (\xs k x -> (k,x):xs) [] m == reverse (List.sort xs)
+
+prop_keysSet :: [(Int, Int)] -> Bool
+prop_keysSet xs =
+  keysSet (fromList xs) == Data.Set.fromList (List.map fst xs)
+
+prop_fromSet :: [(Int, Int)] -> Bool
+prop_fromSet ys =
+  let xs = List.nubBy ((==) `on` fst) ys
+  in fromSet (\k -> fromJust $ List.lookup k xs) (Data.Set.fromList $ List.map fst xs) == fromList xs
diff --git a/tests/seq-properties.hs b/tests/seq-properties.hs
new file mode 100644
--- /dev/null
+++ b/tests/seq-properties.hs
@@ -0,0 +1,592 @@
+import Data.Sequence    -- needs to be compiled with -DTESTING for use here
+
+import Control.Applicative (Applicative(..))
+import Control.Arrow ((***))
+import Data.Foldable (Foldable(..), toList, all, sum)
+import Data.Functor ((<$>), (<$))
+import Data.Maybe
+import Data.Monoid (Monoid(..))
+import Data.Traversable (Traversable(traverse), sequenceA)
+import Prelude hiding (
+  null, length, take, drop, splitAt,
+  foldl, foldl1, foldr, foldr1, scanl, scanl1, scanr, scanr1,
+  filter, reverse, replicate, zip, zipWith, zip3, zipWith3,
+  all, sum)
+import qualified Prelude
+import qualified Data.List
+import Test.QuickCheck hiding ((><))
+import Test.QuickCheck.Poly
+import Test.Framework
+import Test.Framework.Providers.QuickCheck2
+
+
+main :: IO ()
+main = defaultMain
+       [ testProperty "fmap" prop_fmap
+       , testProperty "(<$)" prop_constmap
+       , testProperty "foldr" prop_foldr
+       , testProperty "foldr1" prop_foldr1
+       , testProperty "foldl" prop_foldl
+       , testProperty "foldl1" prop_foldl1
+       , testProperty "(==)" prop_equals
+       , testProperty "compare" prop_compare
+       , testProperty "mappend" prop_mappend
+       , testProperty "singleton" prop_singleton
+       , testProperty "(<|)" prop_cons
+       , testProperty "(|>)" prop_snoc
+       , testProperty "(><)" prop_append
+       , testProperty "fromList" prop_fromList
+       , testProperty "replicate" prop_replicate
+       , testProperty "replicateA" prop_replicateA
+       , testProperty "replicateM" prop_replicateM
+       , testProperty "iterateN" prop_iterateN
+       , testProperty "unfoldr" prop_unfoldr
+       , testProperty "unfoldl" prop_unfoldl
+       , testProperty "null" prop_null
+       , testProperty "length" prop_length
+       , testProperty "viewl" prop_viewl
+       , testProperty "viewr" prop_viewr
+       , testProperty "scanl" prop_scanl
+       , testProperty "scanl1" prop_scanl1
+       , testProperty "scanr" prop_scanr
+       , testProperty "scanr1" prop_scanr1
+       , testProperty "tails" prop_tails
+       , testProperty "inits" prop_inits
+       , testProperty "takeWhileL" prop_takeWhileL
+       , testProperty "takeWhileR" prop_takeWhileR
+       , testProperty "dropWhileL" prop_dropWhileL
+       , testProperty "dropWhileR" prop_dropWhileR
+       , testProperty "spanl" prop_spanl
+       , testProperty "spanr" prop_spanr
+       , testProperty "breakl" prop_breakl
+       , testProperty "breakr" prop_breakr
+       , testProperty "partition" prop_partition
+       , testProperty "filter" prop_filter
+       , testProperty "sort" prop_sort
+       , testProperty "sortBy" prop_sortBy
+       , testProperty "unstableSort" prop_unstableSort
+       , testProperty "unstableSortBy" prop_unstableSortBy
+       , testProperty "index" prop_index
+       , testProperty "adjust" prop_adjust
+       , testProperty "update" prop_update
+       , testProperty "take" prop_take
+       , testProperty "drop" prop_drop
+       , testProperty "splitAt" prop_splitAt
+       , testProperty "elemIndexL" prop_elemIndexL
+       , testProperty "elemIndicesL" prop_elemIndicesL
+       , testProperty "elemIndexR" prop_elemIndexR
+       , testProperty "elemIndicesR" prop_elemIndicesR
+       , testProperty "findIndexL" prop_findIndexL
+       , testProperty "findIndicesL" prop_findIndicesL
+       , testProperty "findIndexR" prop_findIndexR
+       , testProperty "findIndicesR" prop_findIndicesR
+       , testProperty "foldlWithIndex" prop_foldlWithIndex
+       , testProperty "foldrWithIndex" prop_foldrWithIndex
+       , testProperty "mapWithIndex" prop_mapWithIndex
+       , testProperty "reverse" prop_reverse
+       , testProperty "zip" prop_zip
+       , testProperty "zipWith" prop_zipWith
+       , testProperty "zip3" prop_zip3
+       , testProperty "zipWith3" prop_zipWith3
+       , testProperty "zip4" prop_zip4
+       , testProperty "zipWith4" prop_zipWith4
+       ]
+
+------------------------------------------------------------------------
+-- Arbitrary
+------------------------------------------------------------------------
+
+instance Arbitrary a => Arbitrary (Seq a) where
+    arbitrary = Seq <$> arbitrary
+    shrink (Seq x) = map Seq (shrink x)
+
+instance Arbitrary a => Arbitrary (Elem a) where
+    arbitrary = Elem <$> arbitrary
+
+instance (Arbitrary a, Sized a) => Arbitrary (FingerTree a) where
+    arbitrary = sized arb
+      where
+        arb :: (Arbitrary a, Sized a) => Int -> Gen (FingerTree a)
+        arb 0 = return Empty
+        arb 1 = Single <$> arbitrary
+        arb n = deep <$> arbitrary <*> arb (n `div` 2) <*> arbitrary
+
+    shrink (Deep _ (One a) Empty (One b)) = [Single a, Single b]
+    shrink (Deep _ pr m sf) =
+        [deep pr' m sf | pr' <- shrink pr] ++
+        [deep pr m' sf | m' <- shrink m] ++
+        [deep pr m sf' | sf' <- shrink sf]
+    shrink (Single x) = map Single (shrink x)
+    shrink Empty = []
+
+instance (Arbitrary a, Sized a) => Arbitrary (Node a) where
+    arbitrary = oneof [
+        node2 <$> arbitrary <*> arbitrary,
+        node3 <$> arbitrary <*> arbitrary <*> arbitrary]
+
+    shrink (Node2 _ a b) =
+        [node2 a' b | a' <- shrink a] ++
+        [node2 a b' | b' <- shrink b]
+    shrink (Node3 _ a b c) =
+        [node2 a b, node2 a c, node2 b c] ++
+        [node3 a' b c | a' <- shrink a] ++
+        [node3 a b' c | b' <- shrink b] ++
+        [node3 a b c' | c' <- shrink c]
+
+instance Arbitrary a => Arbitrary (Digit a) where
+    arbitrary = oneof [
+        One <$> arbitrary,
+        Two <$> arbitrary <*> arbitrary,
+        Three <$> arbitrary <*> arbitrary <*> arbitrary,
+        Four <$> arbitrary <*> arbitrary <*> arbitrary <*> arbitrary]
+
+    shrink (One a) = map One (shrink a)
+    shrink (Two a b) = [One a, One b]
+    shrink (Three a b c) = [Two a b, Two a c, Two b c]
+    shrink (Four a b c d) = [Three a b c, Three a b d, Three a c d, Three b c d]
+
+------------------------------------------------------------------------
+-- Valid trees
+------------------------------------------------------------------------
+
+class Valid a where
+    valid :: a -> Bool
+
+instance Valid (Elem a) where
+    valid _ = True
+
+instance Valid (Seq a) where
+    valid (Seq xs) = valid xs
+
+instance (Sized a, Valid a) => Valid (FingerTree a) where
+    valid Empty = True
+    valid (Single x) = valid x
+    valid (Deep s pr m sf) =
+        s == size pr + size m + size sf && valid pr && valid m && valid sf
+
+instance (Sized a, Valid a) => Valid (Node a) where
+    valid node = size node == sum (fmap size node) && all valid node
+
+instance Valid a => Valid (Digit a) where
+    valid = all valid
+
+{--------------------------------------------------------------------
+  The general plan is to compare each function with a list equivalent.
+  Each operation should produce a valid tree representing the same
+  sequence as produced by its list counterpart on corresponding inputs.
+  (The list versions are often lazier, but these properties ignore
+  strictness.)
+--------------------------------------------------------------------}
+
+-- utilities for partial conversions
+
+infix 4 ~=
+
+(~=) :: Eq a => Maybe a -> a -> Bool
+(~=) = maybe (const False) (==)
+
+-- Partial conversion of an output sequence to a list.
+toList' :: Seq a -> Maybe [a]
+toList' xs
+  | valid xs = Just (toList xs)
+  | otherwise = Nothing
+
+toListList' :: Seq (Seq a) -> Maybe [[a]]
+toListList' xss = toList' xss >>= mapM toList'
+
+toListPair' :: (Seq a, Seq b) -> Maybe ([a], [b])
+toListPair' (xs, ys) = (,) <$> toList' xs <*> toList' ys
+
+-- instances
+
+prop_fmap :: Seq Int -> Bool
+prop_fmap xs =
+    toList' (fmap f xs) ~= map f (toList xs)
+  where f = (+100)
+
+prop_constmap :: A -> Seq A -> Bool
+prop_constmap x xs =
+    toList' (x <$ xs) ~= map (const x) (toList xs)
+
+prop_foldr :: Seq A -> Bool
+prop_foldr xs =
+    foldr f z xs == Prelude.foldr f z (toList xs)
+  where
+    f = (:)
+    z = []
+
+prop_foldr1 :: Seq Int -> Property
+prop_foldr1 xs =
+    not (null xs) ==> foldr1 f xs == Data.List.foldr1 f (toList xs)
+  where f = (-)
+
+prop_foldl :: Seq A -> Bool
+prop_foldl xs =
+    foldl f z xs == Prelude.foldl f z (toList xs)
+  where
+    f = flip (:)
+    z = []
+
+prop_foldl1 :: Seq Int -> Property
+prop_foldl1 xs =
+    not (null xs) ==> foldl1 f xs == Data.List.foldl1 f (toList xs)
+  where f = (-)
+
+prop_equals :: Seq OrdA -> Seq OrdA -> Bool
+prop_equals xs ys =
+    (xs == ys) == (toList xs == toList ys)
+
+prop_compare :: Seq OrdA -> Seq OrdA -> Bool
+prop_compare xs ys =
+    compare xs ys == compare (toList xs) (toList ys)
+
+prop_mappend :: Seq A -> Seq A -> Bool
+prop_mappend xs ys =
+    toList' (mappend xs ys) ~= toList xs ++ toList ys
+
+-- * Construction
+
+{-
+    toList' empty ~= []
+-}
+
+prop_singleton :: A -> Bool
+prop_singleton x =
+    toList' (singleton x) ~= [x]
+
+prop_cons :: A -> Seq A -> Bool
+prop_cons x xs =
+    toList' (x <| xs) ~= x : toList xs
+
+prop_snoc :: Seq A -> A -> Bool
+prop_snoc xs x =
+    toList' (xs |> x) ~= toList xs ++ [x]
+
+prop_append :: Seq A -> Seq A -> Bool
+prop_append xs ys =
+    toList' (xs >< ys) ~= toList xs ++ toList ys
+
+prop_fromList :: [A] -> Bool
+prop_fromList xs =
+    toList' (fromList xs) ~= xs
+
+-- ** Repetition
+
+prop_replicate :: NonNegative Int -> A -> Bool
+prop_replicate (NonNegative m) x =
+    toList' (replicate n x) ~= Prelude.replicate n x
+  where n = m `mod` 10000
+
+prop_replicateA :: NonNegative Int -> Bool
+prop_replicateA (NonNegative m) =
+    traverse toList' (replicateA n a) ~= sequenceA (Prelude.replicate n a)
+  where
+    n = m `mod` 10000
+    a = Action 1 0 :: M Int
+
+prop_replicateM :: NonNegative Int -> Bool
+prop_replicateM (NonNegative m) =
+    traverse toList' (replicateM n a) ~= sequence (Prelude.replicate n a)
+  where
+    n = m `mod` 10000
+    a = Action 1 0 :: M Int
+
+-- ** Iterative construction
+
+prop_iterateN :: NonNegative Int -> Int -> Bool
+prop_iterateN (NonNegative m) x =
+    toList' (iterateN n f x) ~= Prelude.take n (Prelude.iterate f x)
+  where
+    n = m `mod` 10000
+    f = (+1)
+
+prop_unfoldr :: [A] -> Bool
+prop_unfoldr z =
+    toList' (unfoldr f z) ~= Data.List.unfoldr f z
+  where
+    f [] = Nothing
+    f (x:xs) = Just (x, xs)
+
+prop_unfoldl :: [A] -> Bool
+prop_unfoldl z =
+    toList' (unfoldl f z) ~= Data.List.reverse (Data.List.unfoldr (fmap swap . f) z)
+  where
+    f [] = Nothing
+    f (x:xs) = Just (xs, x)
+    swap (x,y) = (y,x)
+
+-- * Deconstruction
+
+-- ** Queries
+
+prop_null :: Seq A -> Bool
+prop_null xs =
+    null xs == Prelude.null (toList xs)
+
+prop_length :: Seq A -> Bool
+prop_length xs =
+    length xs == Prelude.length (toList xs)
+
+-- ** Views
+
+prop_viewl :: Seq A -> Bool
+prop_viewl xs =
+    case viewl xs of
+    EmptyL ->   Prelude.null (toList xs)
+    x :< xs' -> valid xs' && toList xs == x : toList xs'
+
+prop_viewr :: Seq A -> Bool
+prop_viewr xs =
+    case viewr xs of
+    EmptyR ->   Prelude.null (toList xs)
+    xs' :> x -> valid xs' && toList xs == toList xs' ++ [x]
+
+-- * Scans
+
+prop_scanl :: [A] -> Seq A -> Bool
+prop_scanl z xs =
+    toList' (scanl f z xs) ~= Data.List.scanl f z (toList xs)
+  where f = flip (:)
+
+prop_scanl1 :: Seq Int -> Property
+prop_scanl1 xs =
+    not (null xs) ==> toList' (scanl1 f xs) ~= Data.List.scanl1 f (toList xs)
+  where f = (-)
+
+prop_scanr :: [A] -> Seq A -> Bool
+prop_scanr z xs =
+    toList' (scanr f z xs) ~= Data.List.scanr f z (toList xs)
+  where f = (:)
+
+prop_scanr1 :: Seq Int -> Property
+prop_scanr1 xs =
+    not (null xs) ==> toList' (scanr1 f xs) ~= Data.List.scanr1 f (toList xs)
+  where f = (-)
+
+-- * Sublists
+
+prop_tails :: Seq A -> Bool
+prop_tails xs =
+    toListList' (tails xs) ~= Data.List.tails (toList xs)
+
+prop_inits :: Seq A -> Bool
+prop_inits xs =
+    toListList' (inits xs) ~= Data.List.inits (toList xs)
+
+-- ** Sequential searches
+-- We use predicates with varying density.
+
+prop_takeWhileL :: Positive Int -> Seq Int -> Bool
+prop_takeWhileL (Positive n) xs =
+    toList' (takeWhileL p xs) ~= Prelude.takeWhile p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_takeWhileR :: Positive Int -> Seq Int -> Bool
+prop_takeWhileR (Positive n) xs =
+    toList' (takeWhileR p xs) ~= Prelude.reverse (Prelude.takeWhile p (Prelude.reverse (toList xs)))
+  where p x = x `mod` n == 0
+
+prop_dropWhileL :: Positive Int -> Seq Int -> Bool
+prop_dropWhileL (Positive n) xs =
+    toList' (dropWhileL p xs) ~= Prelude.dropWhile p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_dropWhileR :: Positive Int -> Seq Int -> Bool
+prop_dropWhileR (Positive n) xs =
+    toList' (dropWhileR p xs) ~= Prelude.reverse (Prelude.dropWhile p (Prelude.reverse (toList xs)))
+  where p x = x `mod` n == 0
+
+prop_spanl :: Positive Int -> Seq Int -> Bool
+prop_spanl (Positive n) xs =
+    toListPair' (spanl p xs) ~= Data.List.span p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_spanr :: Positive Int -> Seq Int -> Bool
+prop_spanr (Positive n) xs =
+    toListPair' (spanr p xs) ~= (Prelude.reverse *** Prelude.reverse) (Data.List.span p (Prelude.reverse (toList xs)))
+  where p x = x `mod` n == 0
+
+prop_breakl :: Positive Int -> Seq Int -> Bool
+prop_breakl (Positive n) xs =
+    toListPair' (breakl p xs) ~= Data.List.break p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_breakr :: Positive Int -> Seq Int -> Bool
+prop_breakr (Positive n) xs =
+    toListPair' (breakr p xs) ~= (Prelude.reverse *** Prelude.reverse) (Data.List.break p (Prelude.reverse (toList xs)))
+  where p x = x `mod` n == 0
+
+prop_partition :: Positive Int -> Seq Int -> Bool
+prop_partition (Positive n) xs =
+    toListPair' (partition p xs) ~= Data.List.partition p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_filter :: Positive Int -> Seq Int -> Bool
+prop_filter (Positive n) xs =
+    toList' (filter p xs) ~= Prelude.filter p (toList xs)
+  where p x = x `mod` n == 0
+
+-- * Sorting
+
+prop_sort :: Seq OrdA -> Bool
+prop_sort xs =
+    toList' (sort xs) ~= Data.List.sort (toList xs)
+
+prop_sortBy :: Seq (OrdA, B) -> Bool
+prop_sortBy xs =
+    toList' (sortBy f xs) ~= Data.List.sortBy f (toList xs)
+  where f (x1, _) (x2, _) = compare x1 x2
+
+prop_unstableSort :: Seq OrdA -> Bool
+prop_unstableSort xs =
+    toList' (unstableSort xs) ~= Data.List.sort (toList xs)
+
+prop_unstableSortBy :: Seq OrdA -> Bool
+prop_unstableSortBy xs =
+    toList' (unstableSortBy compare xs) ~= Data.List.sort (toList xs)
+
+-- * Indexing
+
+prop_index :: Seq A -> Property
+prop_index xs =
+    not (null xs) ==> forAll (choose (0, length xs-1)) $ \ i ->
+    index xs i == toList xs !! i
+
+prop_adjust :: Int -> Int -> Seq Int -> Bool
+prop_adjust n i xs =
+    toList' (adjust f i xs) ~= adjustList f i (toList xs)
+  where f = (+n)
+
+prop_update :: Int -> A -> Seq A -> Bool
+prop_update i x xs =
+    toList' (update i x xs) ~= adjustList (const x) i (toList xs)
+
+prop_take :: Int -> Seq A -> Bool
+prop_take n xs =
+    toList' (take n xs) ~= Prelude.take n (toList xs)
+
+prop_drop :: Int -> Seq A -> Bool
+prop_drop n xs =
+    toList' (drop n xs) ~= Prelude.drop n (toList xs)
+
+prop_splitAt :: Int -> Seq A -> Bool
+prop_splitAt n xs =
+    toListPair' (splitAt n xs) ~= Prelude.splitAt n (toList xs)
+
+adjustList :: (a -> a) -> Int -> [a] -> [a]
+adjustList f i xs =
+    [if j == i then f x else x | (j, x) <- Prelude.zip [0..] xs]
+
+-- ** Indexing with predicates
+-- The elem* tests have poor coverage, but for find* we use predicates
+-- of varying density.
+
+prop_elemIndexL :: A -> Seq A -> Bool
+prop_elemIndexL x xs =
+    elemIndexL x xs == Data.List.elemIndex x (toList xs)
+
+prop_elemIndicesL :: A -> Seq A -> Bool
+prop_elemIndicesL x xs =
+    elemIndicesL x xs == Data.List.elemIndices x (toList xs)
+
+prop_elemIndexR :: A -> Seq A -> Bool
+prop_elemIndexR x xs =
+    elemIndexR x xs == listToMaybe (Prelude.reverse (Data.List.elemIndices x (toList xs)))
+
+prop_elemIndicesR :: A -> Seq A -> Bool
+prop_elemIndicesR x xs =
+    elemIndicesR x xs == Prelude.reverse (Data.List.elemIndices x (toList xs))
+
+prop_findIndexL :: Positive Int -> Seq Int -> Bool
+prop_findIndexL (Positive n) xs =
+    findIndexL p xs == Data.List.findIndex p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_findIndicesL :: Positive Int -> Seq Int -> Bool
+prop_findIndicesL (Positive n) xs =
+    findIndicesL p xs == Data.List.findIndices p (toList xs)
+  where p x = x `mod` n == 0
+
+prop_findIndexR :: Positive Int -> Seq Int -> Bool
+prop_findIndexR (Positive n) xs =
+    findIndexR p xs == listToMaybe (Prelude.reverse (Data.List.findIndices p (toList xs)))
+  where p x = x `mod` n == 0
+
+prop_findIndicesR :: Positive Int -> Seq Int -> Bool
+prop_findIndicesR (Positive n) xs =
+    findIndicesR p xs == Prelude.reverse (Data.List.findIndices p (toList xs))
+  where p x = x `mod` n == 0
+
+-- * Folds
+
+prop_foldlWithIndex :: [(Int, A)] -> Seq A -> Bool
+prop_foldlWithIndex z xs =
+    foldlWithIndex f z xs == Data.List.foldl (uncurry . f) z (Data.List.zip [0..] (toList xs))
+  where f ys n y = (n,y):ys
+
+prop_foldrWithIndex :: [(Int, A)] -> Seq A -> Bool
+prop_foldrWithIndex z xs =
+    foldrWithIndex f z xs == Data.List.foldr (uncurry f) z (Data.List.zip [0..] (toList xs))
+  where f n y ys = (n,y):ys
+
+-- * Transformations
+
+prop_mapWithIndex :: Seq A -> Bool
+prop_mapWithIndex xs =
+    toList' (mapWithIndex f xs) ~= map (uncurry f) (Data.List.zip [0..] (toList xs))
+  where f = (,)
+
+prop_reverse :: Seq A -> Bool
+prop_reverse xs =
+    toList' (reverse xs) ~= Prelude.reverse (toList xs)
+
+-- ** Zips
+
+prop_zip :: Seq A -> Seq B -> Bool
+prop_zip xs ys =
+    toList' (zip xs ys) ~= Prelude.zip (toList xs) (toList ys)
+
+prop_zipWith :: Seq A -> Seq B -> Bool
+prop_zipWith xs ys =
+    toList' (zipWith f xs ys) ~= Prelude.zipWith f (toList xs) (toList ys)
+  where f = (,)
+
+prop_zip3 :: Seq A -> Seq B -> Seq C -> Bool
+prop_zip3 xs ys zs =
+    toList' (zip3 xs ys zs) ~= Prelude.zip3 (toList xs) (toList ys) (toList zs)
+
+prop_zipWith3 :: Seq A -> Seq B -> Seq C -> Bool
+prop_zipWith3 xs ys zs =
+    toList' (zipWith3 f xs ys zs) ~= Prelude.zipWith3 f (toList xs) (toList ys) (toList zs)
+  where f = (,,)
+
+prop_zip4 :: Seq A -> Seq B -> Seq C -> Seq Int -> Bool
+prop_zip4 xs ys zs ts =
+    toList' (zip4 xs ys zs ts) ~= Data.List.zip4 (toList xs) (toList ys) (toList zs) (toList ts)
+
+prop_zipWith4 :: Seq A -> Seq B -> Seq C -> Seq Int -> Bool
+prop_zipWith4 xs ys zs ts =
+    toList' (zipWith4 f xs ys zs ts) ~= Data.List.zipWith4 f (toList xs) (toList ys) (toList zs) (toList ts)
+  where f = (,,,)
+
+-- Simple test monad
+
+data M a = Action Int a
+    deriving (Eq, Show)
+
+instance Functor M where
+    fmap f (Action n x) = Action n (f x)
+
+instance Applicative M where
+    pure x = Action 0 x
+    Action m f <*> Action n x = Action (m+n) (f x)
+
+instance Monad M where
+    return x = Action 0 x
+    Action m x >>= f = let Action n y = f x in Action (m+n) y
+
+instance Foldable M where
+    foldMap f (Action _ x) = f x
+
+instance Traversable M where
+    traverse f (Action n x) = Action n <$> f x
diff --git a/tests/set-properties.hs b/tests/set-properties.hs
new file mode 100644
--- /dev/null
+++ b/tests/set-properties.hs
@@ -0,0 +1,378 @@
+import qualified Data.IntSet as IntSet
+import Data.List (nub,sort)
+import qualified Data.List as List
+import Data.Monoid (mempty)
+import Data.Maybe
+import Data.Set
+import Prelude hiding (lookup, null, map, filter, foldr, foldl)
+import Test.Framework
+import Test.Framework.Providers.HUnit
+import Test.Framework.Providers.QuickCheck2
+import Test.HUnit hiding (Test, Testable)
+import Test.QuickCheck
+
+main :: IO ()
+main = defaultMain [ testCase "lookupLT" test_lookupLT
+                   , testCase "lookupGT" test_lookupGT
+                   , testCase "lookupLE" test_lookupLE
+                   , testCase "lookupGE" test_lookupGE
+                   , testCase "lookupIndex" test_lookupIndex
+                   , testCase "findIndex" test_findIndex
+                   , testCase "elemAt" test_elemAt
+                   , testCase "deleteAt" test_deleteAt
+                   , testProperty "prop_Valid" prop_Valid
+                   , testProperty "prop_Single" prop_Single
+                   , testProperty "prop_Member" prop_Member
+                   , testProperty "prop_NotMember" prop_NotMember
+                   , testProperty "prop_LookupLT" prop_LookupLT
+                   , testProperty "prop_LookupGT" prop_LookupGT
+                   , testProperty "prop_LookupLE" prop_LookupLE
+                   , testProperty "prop_LookupGE" prop_LookupGE
+                   , testProperty "prop_InsertValid" prop_InsertValid
+                   , testProperty "prop_InsertDelete" prop_InsertDelete
+                   , testProperty "prop_DeleteValid" prop_DeleteValid
+                   , testProperty "prop_Link" prop_Link
+                   , testProperty "prop_Merge" prop_Merge
+                   , testProperty "prop_UnionValid" prop_UnionValid
+                   , testProperty "prop_UnionInsert" prop_UnionInsert
+                   , testProperty "prop_UnionAssoc" prop_UnionAssoc
+                   , testProperty "prop_UnionComm" prop_UnionComm
+                   , testProperty "prop_DiffValid" prop_DiffValid
+                   , testProperty "prop_Diff" prop_Diff
+                   , testProperty "prop_IntValid" prop_IntValid
+                   , testProperty "prop_Int" prop_Int
+                   , testProperty "prop_Ordered" prop_Ordered
+                   , testProperty "prop_List" prop_List
+                   , testProperty "prop_DescList" prop_DescList
+                   , testProperty "prop_AscDescList" prop_AscDescList
+                   , testProperty "prop_fromList" prop_fromList
+                   , testProperty "prop_isProperSubsetOf" prop_isProperSubsetOf
+                   , testProperty "prop_isProperSubsetOf2" prop_isProperSubsetOf2
+                   , testProperty "prop_isSubsetOf" prop_isSubsetOf
+                   , testProperty "prop_isSubsetOf2" prop_isSubsetOf2
+                   , testProperty "prop_size" prop_size
+                   , testProperty "prop_findMax" prop_findMax
+                   , testProperty "prop_findMin" prop_findMin
+                   , testProperty "prop_ord" prop_ord
+                   , testProperty "prop_readShow" prop_readShow
+                   , testProperty "prop_foldR" prop_foldR
+                   , testProperty "prop_foldR'" prop_foldR'
+                   , testProperty "prop_foldL" prop_foldL
+                   , testProperty "prop_foldL'" prop_foldL'
+                   , testProperty "prop_map" prop_map
+                   , testProperty "prop_maxView" prop_maxView
+                   , testProperty "prop_minView" prop_minView
+                   , testProperty "prop_split" prop_split
+                   , testProperty "prop_splitMember" prop_splitMember
+                   , testProperty "prop_splitRoot" prop_splitRoot
+                   , testProperty "prop_partition" prop_partition
+                   , testProperty "prop_filter" prop_filter
+                   ]
+
+----------------------------------------------------------------
+-- Unit tests
+----------------------------------------------------------------
+
+test_lookupLT :: Assertion
+test_lookupLT = do
+    lookupLT 3 (fromList [3, 5]) @?= Nothing
+    lookupLT 5 (fromList [3, 5]) @?= Just 3
+
+test_lookupGT :: Assertion
+test_lookupGT = do
+   lookupGT 4 (fromList [3, 5]) @?= Just 5
+   lookupGT 5 (fromList [3, 5]) @?= Nothing
+
+test_lookupLE :: Assertion
+test_lookupLE = do
+   lookupLE 2 (fromList [3, 5]) @?= Nothing
+   lookupLE 4 (fromList [3, 5]) @?= Just 3
+   lookupLE 5 (fromList [3, 5]) @?= Just 5
+
+test_lookupGE :: Assertion
+test_lookupGE = do
+   lookupGE 3 (fromList [3, 5]) @?= Just 3
+   lookupGE 4 (fromList [3, 5]) @?= Just 5
+   lookupGE 6 (fromList [3, 5]) @?= Nothing
+
+{--------------------------------------------------------------------
+  Indexed
+--------------------------------------------------------------------}
+
+test_lookupIndex :: Assertion
+test_lookupIndex = do
+    isJust   (lookupIndex 2 (fromList [5,3])) @?= False
+    fromJust (lookupIndex 3 (fromList [5,3])) @?= 0
+    fromJust (lookupIndex 5 (fromList [5,3])) @?= 1
+    isJust   (lookupIndex 6 (fromList [5,3])) @?= False
+
+test_findIndex :: Assertion
+test_findIndex = do
+    findIndex 3 (fromList [5,3]) @?= 0
+    findIndex 5 (fromList [5,3]) @?= 1
+
+test_elemAt :: Assertion
+test_elemAt = do
+    elemAt 0 (fromList [5,3]) @?= 3
+    elemAt 1 (fromList [5,3]) @?= 5
+
+test_deleteAt :: Assertion
+test_deleteAt = do
+    deleteAt 0 (fromList [5,3]) @?= singleton 5
+    deleteAt 1 (fromList [5,3]) @?= singleton 3
+
+{--------------------------------------------------------------------
+  Arbitrary, reasonably balanced trees
+--------------------------------------------------------------------}
+instance (Enum a) => Arbitrary (Set a) where
+    arbitrary = sized (arbtree 0 maxkey)
+      where maxkey = 10000
+
+            arbtree :: (Enum a) => Int -> Int -> Int -> Gen (Set a)
+            arbtree lo hi n = do t <- gentree lo hi n
+                                 if balanced t then return t else arbtree lo hi n
+              where gentree lo hi n
+                      | n <= 0    = return Tip
+                      | lo >= hi  = return Tip
+                      | otherwise = do  i  <- choose (lo,hi)
+                                        m  <- choose (1,70)
+                                        let (ml,mr) | m==(1::Int) = (1,2)
+                                                    | m==2        = (2,1)
+                                                    | m==3        = (1,1)
+                                                    | otherwise   = (2,2)
+                                        l  <- gentree lo (i-1) (n `div` ml)
+                                        r  <- gentree (i+1) hi (n `div` mr)
+                                        return (bin (toEnum i) l r)
+
+{--------------------------------------------------------------------
+  Valid tree's
+--------------------------------------------------------------------}
+forValid :: (Enum a,Show a,Testable b) => (Set a -> b) -> Property
+forValid f = forAll arbitrary $ \t ->
+--    classify (balanced t) "balanced" $
+    classify (size t == 0) "empty" $
+    classify (size t > 0  && size t <= 10) "small" $
+    classify (size t > 10 && size t <= 64) "medium" $
+    classify (size t > 64) "large" $
+    balanced t ==> f t
+
+forValidUnitTree :: Testable a => (Set Int -> a) -> Property
+forValidUnitTree f = forValid f
+
+prop_Valid :: Property
+prop_Valid = forValidUnitTree $ \t -> valid t
+
+{--------------------------------------------------------------------
+  Single, Member, Insert, Delete
+--------------------------------------------------------------------}
+prop_Single :: Int -> Bool
+prop_Single x = (insert x empty == singleton x)
+
+prop_Member :: [Int] -> Int -> Bool
+prop_Member xs n =
+  let m  = fromList xs
+  in all (\k -> k `member` m == (k `elem` xs)) (n : xs)
+
+prop_NotMember :: [Int] -> Int -> Bool
+prop_NotMember xs n =
+  let m  = fromList xs
+  in all (\k -> k `notMember` m == (k `notElem` xs)) (n : xs)
+
+test_LookupSomething :: (Int -> Set Int -> Maybe Int) -> (Int -> Int -> Bool) -> [Int] -> Bool
+test_LookupSomething lookup' cmp xs =
+  let odd_sorted_xs = filter_odd $ nub $ sort xs
+      t = fromList odd_sorted_xs
+      test x = case List.filter (`cmp` x) odd_sorted_xs of
+                 []             -> lookup' x t == Nothing
+                 cs | 0 `cmp` 1 -> lookup' x t == Just (last cs) -- we want largest such element
+                    | otherwise -> lookup' x t == Just (head cs) -- we want smallest such element
+  in all test xs
+
+  where filter_odd [] = []
+        filter_odd [_] = []
+        filter_odd (_ : o : xs) = o : filter_odd xs
+
+prop_LookupLT :: [Int] -> Bool
+prop_LookupLT = test_LookupSomething lookupLT (<)
+
+prop_LookupGT :: [Int] -> Bool
+prop_LookupGT = test_LookupSomething lookupGT (>)
+
+prop_LookupLE :: [Int] -> Bool
+prop_LookupLE = test_LookupSomething lookupLE (<=)
+
+prop_LookupGE :: [Int] -> Bool
+prop_LookupGE = test_LookupSomething lookupGE (>=)
+
+prop_InsertValid :: Int -> Property
+prop_InsertValid k = forValidUnitTree $ \t -> valid (insert k t)
+
+prop_InsertDelete :: Int -> Set Int -> Property
+prop_InsertDelete k t = not (member k t) ==> delete k (insert k t) == t
+
+prop_DeleteValid :: Int -> Property
+prop_DeleteValid k = forValidUnitTree $ \t -> valid (delete k (insert k t))
+
+{--------------------------------------------------------------------
+  Balance
+--------------------------------------------------------------------}
+prop_Link :: Int -> Property
+prop_Link x = forValidUnitTree $ \t ->
+    let (l,r) = split x t
+    in valid (link x l r)
+
+prop_Merge :: Int -> Property
+prop_Merge x = forValidUnitTree $ \t ->
+    let (l,r) = split x t
+    in valid (merge l r)
+
+{--------------------------------------------------------------------
+  Union
+--------------------------------------------------------------------}
+prop_UnionValid :: Property
+prop_UnionValid
+  = forValidUnitTree $ \t1 ->
+    forValidUnitTree $ \t2 ->
+    valid (union t1 t2)
+
+prop_UnionInsert :: Int -> Set Int -> Bool
+prop_UnionInsert x t = union t (singleton x) == insert x t
+
+prop_UnionAssoc :: Set Int -> Set Int -> Set Int -> Bool
+prop_UnionAssoc t1 t2 t3 = union t1 (union t2 t3) == union (union t1 t2) t3
+
+prop_UnionComm :: Set Int -> Set Int -> Bool
+prop_UnionComm t1 t2 = (union t1 t2 == union t2 t1)
+
+prop_DiffValid :: Property
+prop_DiffValid = forValidUnitTree $ \t1 ->
+    forValidUnitTree $ \t2 ->
+    valid (difference t1 t2)
+
+prop_Diff :: [Int] -> [Int] -> Bool
+prop_Diff xs ys = toAscList (difference (fromList xs) (fromList ys))
+                  == List.sort ((List.\\) (nub xs)  (nub ys))
+
+prop_IntValid :: Property
+prop_IntValid = forValidUnitTree $ \t1 ->
+    forValidUnitTree $ \t2 ->
+    valid (intersection t1 t2)
+
+prop_Int :: [Int] -> [Int] -> Bool
+prop_Int xs ys = toAscList (intersection (fromList xs) (fromList ys))
+                 == List.sort (nub ((List.intersect) (xs)  (ys)))
+
+{--------------------------------------------------------------------
+  Lists
+--------------------------------------------------------------------}
+prop_Ordered :: Property
+prop_Ordered = forAll (choose (5,100)) $ \n ->
+    let xs = [0..n::Int]
+    in fromAscList xs == fromList xs
+
+prop_List :: [Int] -> Bool
+prop_List xs = (sort (nub xs) == toList (fromList xs))
+
+prop_DescList :: [Int] -> Bool
+prop_DescList xs = (reverse (sort (nub xs)) == toDescList (fromList xs))
+
+prop_AscDescList :: [Int] -> Bool
+prop_AscDescList xs = toAscList s == reverse (toDescList s)
+  where s = fromList xs
+
+prop_fromList :: [Int] -> Bool
+prop_fromList xs
+  = case fromList xs of
+      t -> t == fromAscList sort_xs &&
+           t == fromDistinctAscList nub_sort_xs &&
+           t == List.foldr insert empty xs
+  where sort_xs = sort xs
+        nub_sort_xs = List.map List.head $ List.group sort_xs
+
+{--------------------------------------------------------------------
+  Set operations are like IntSet operations
+--------------------------------------------------------------------}
+toIntSet :: Set Int -> IntSet.IntSet
+toIntSet = IntSet.fromList . toList
+
+-- Check that Set Int.isProperSubsetOf is the same as Set.isProperSubsetOf.
+prop_isProperSubsetOf :: Set Int -> Set Int -> Bool
+prop_isProperSubsetOf a b = isProperSubsetOf a b == IntSet.isProperSubsetOf (toIntSet a) (toIntSet b)
+
+-- In the above test, isProperSubsetOf almost always returns False (since a
+-- random set is almost never a subset of another random set).  So this second
+-- test checks the True case.
+prop_isProperSubsetOf2 :: Set Int -> Set Int -> Bool
+prop_isProperSubsetOf2 a b = isProperSubsetOf a c == (a /= c) where
+  c = union a b
+
+prop_isSubsetOf :: Set Int -> Set Int -> Bool
+prop_isSubsetOf a b = isSubsetOf a b == IntSet.isSubsetOf (toIntSet a) (toIntSet b)
+
+prop_isSubsetOf2 :: Set Int -> Set Int -> Bool
+prop_isSubsetOf2 a b = isSubsetOf a (union a b)
+
+prop_size :: Set Int -> Bool
+prop_size s = size s == List.length (toList s)
+
+prop_findMax :: Set Int -> Property
+prop_findMax s = not (null s) ==> findMax s == maximum (toList s)
+
+prop_findMin :: Set Int -> Property
+prop_findMin s = not (null s) ==> findMin s == minimum (toList s)
+
+prop_ord :: Set Int -> Set Int -> Bool
+prop_ord s1 s2 = s1 `compare` s2 == toList s1 `compare` toList s2
+
+prop_readShow :: Set Int -> Bool
+prop_readShow s = s == read (show s)
+
+prop_foldR :: Set Int -> Bool
+prop_foldR s = foldr (:) [] s == toList s
+
+prop_foldR' :: Set Int -> Bool
+prop_foldR' s = foldr' (:) [] s == toList s
+
+prop_foldL :: Set Int -> Bool
+prop_foldL s = foldl (flip (:)) [] s == List.foldl (flip (:)) [] (toList s)
+
+prop_foldL' :: Set Int -> Bool
+prop_foldL' s = foldl' (flip (:)) [] s == List.foldl' (flip (:)) [] (toList s)
+
+prop_map :: Set Int -> Bool
+prop_map s = map id s == s
+
+prop_maxView :: Set Int -> Bool
+prop_maxView s = case maxView s of
+    Nothing -> null s
+    Just (m,s') -> m == maximum (toList s) && s == insert m s' && m `notMember` s'
+
+prop_minView :: Set Int -> Bool
+prop_minView s = case minView s of
+    Nothing -> null s
+    Just (m,s') -> m == minimum (toList s) && s == insert m s' && m `notMember` s'
+
+prop_split :: Set Int -> Int -> Bool
+prop_split s i = case split i s of
+    (s1,s2) -> all (<i) (toList s1) && all (>i) (toList s2) && i `delete` s == union s1 s2
+
+prop_splitMember :: Set Int -> Int -> Bool
+prop_splitMember s i = case splitMember i s of
+    (s1,t,s2) -> all (<i) (toList s1) && all (>i) (toList s2) && t == i `member` s && i `delete` s == union s1 s2
+
+prop_splitRoot :: Set Int -> Bool
+prop_splitRoot s = loop ls && (s == unions ls)
+ where
+  ls = splitRoot s
+  loop [] = True
+  loop (s1:rst) = List.null
+                  [ (x,y) | x <- toList s1
+                          , y <- toList (unions rst)
+                          , x > y ]
+
+prop_partition :: Set Int -> Int -> Bool
+prop_partition s i = case partition odd s of
+    (s1,s2) -> all odd (toList s1) && all even (toList s2) && s == s1 `union` s2
+
+prop_filter :: Set Int -> Int -> Bool
+prop_filter s i = partition odd s == (filter odd s, filter even s)
