diff --git a/pred-trie.cabal b/pred-trie.cabal
--- a/pred-trie.cabal
+++ b/pred-trie.cabal
@@ -1,11 +1,12 @@
 Name:                   pred-trie
-Version:                0.1
+Version:                0.2.0
 Author:                 Athan Clark <athan.clark@gmail.com>
 Maintainer:             Athan Clark <athan.clark@gmail.com>
 License:                BSD3
 License-File:           LICENSE
+Category:               Data
 Synopsis:               Predicative tries
--- Description:            
+-- Description:
 Cabal-Version:          >= 1.10
 Build-Type:             Simple
 
diff --git a/src/Data/Trie/Pred/Disjoint.hs b/src/Data/Trie/Pred/Disjoint.hs
--- a/src/Data/Trie/Pred/Disjoint.hs
+++ b/src/Data/Trie/Pred/Disjoint.hs
@@ -2,6 +2,7 @@
   ( RDPTrie (..)
   , merge
   , lookup
+  , lookupWithL
   , lookupNearestParent
   , litSingleton
   , litExtrude
@@ -9,7 +10,7 @@
   ) where
 
 import Prelude hiding (lookup)
-import Data.Trie.Pred.Disjoint.Tail hiding (lookup, lookupNearestParent, merge)
+import Data.Trie.Pred.Disjoint.Tail hiding (lookup, lookupWithL, lookupNearestParent, merge)
 import qualified Data.Trie.Pred.Disjoint.Tail as ND
 import Data.Monoid
 import qualified Data.List.NonEmpty as NE
@@ -35,6 +36,10 @@
 lookup [] (Rooted mx _) = mx
 lookup ts (Rooted _ xs) = firstJust $ map (ND.lookup $ NE.fromList ts) xs
 
+lookupWithL :: (Eq t) => (t -> t) -> [t] -> RDPTrie p t x -> Maybe x
+lookupWithL _ [] (Rooted mx _) = mx
+lookupWithL f ts (Rooted _ xs) = firstJust $ map (ND.lookupWithL f $ NE.fromList ts) xs
+
 lookupNearestParent :: (Eq t) => [t] -> RDPTrie p t x -> Maybe x
 lookupNearestParent [] (Rooted mx _) = mx
 lookupNearestParent ts (Rooted mx xs) =
@@ -57,4 +62,3 @@
 litExtrude ts (Rooted mx xs) = Rooted Nothing [ND.litExtrudeTail (init ts) $
                                                  DMore (last ts) mx xs
                                               ]
-
diff --git a/src/Data/Trie/Pred/Disjoint/Tail.hs b/src/Data/Trie/Pred/Disjoint/Tail.hs
--- a/src/Data/Trie/Pred/Disjoint/Tail.hs
+++ b/src/Data/Trie/Pred/Disjoint/Tail.hs
@@ -5,6 +5,7 @@
 module Data.Trie.Pred.Disjoint.Tail
   ( DPTrie (..)
   , lookup
+  , lookupWithL
   , lookupNearestParent
   , merge
   , areDisjoint
@@ -66,6 +67,19 @@
       [] -> ($ r) <$> mrx
       _  -> ($ r) <$> firstJust (map (lookup $ NE.fromList ts) xrs)
 
+lookupWithL :: Eq t => (t -> t) -> NonEmpty t -> DPTrie p t x -> Maybe x
+lookupWithL f (t:|ts) (DMore t' mx xs)
+  | null ts = if f t == t'
+              then mx
+              else Nothing
+  | otherwise = if t == t'
+                then firstJust $ map (lookupWithL f $ NE.fromList ts) xs
+                else Nothing
+lookupWithL f (t:|ts) (DPred _ p mrx xrs) =
+  p t >>=
+    \r -> case ts of
+      [] -> ($ r) <$> mrx
+      _  -> ($ r) <$> firstJust (map (lookupWithL f $ NE.fromList ts) xrs)
 
 lookupNearestParent :: Eq t => NonEmpty t -> DPTrie p t x -> Maybe x
 lookupNearestParent tss@(t:|ts) trie@(DMore t' mx xs) = case lookup tss trie of
diff --git a/src/Data/Trie/Pred/Unified.hs b/src/Data/Trie/Pred/Unified.hs
--- a/src/Data/Trie/Pred/Unified.hs
+++ b/src/Data/Trie/Pred/Unified.hs
@@ -4,6 +4,7 @@
   , showTrie
   , merge
   , lookup
+  , lookupWithL
   , lookupNearestParent
   , litSingleton
   , litExtrude
@@ -11,7 +12,7 @@
   ) where
 
 import Prelude hiding (lookup)
-import Data.Trie.Pred.Unified.Tail hiding (lookup, lookupNearestParent, merge, assignLit)
+import Data.Trie.Pred.Unified.Tail hiding (lookup, lookupWithL, lookupNearestParent, merge, assignLit)
 import qualified Data.Trie.Pred.Unified.Tail as NU
 import Data.Monoid
 import Data.Maybe (fromMaybe)
@@ -50,6 +51,10 @@
 lookup :: (Eq t) => [t] -> RUPTrie t x -> Maybe x
 lookup [] (Rooted mx _) = mx
 lookup ts (Rooted _ xs) = firstJust $ map (NU.lookup $ NE.fromList ts) xs
+
+lookupWithL :: (Eq t) => (t -> t) -> [t] -> RUPTrie t x -> Maybe x
+lookupWithL _ [] (Rooted mx _) = mx
+lookupWithL f ts (Rooted _ xs) = firstJust $ map (NU.lookupWithL f $ NE.fromList ts) xs
 
 lookupNearestParent :: (Eq t) => [t] -> RUPTrie t x -> Maybe x
 lookupNearestParent [] (Rooted mx _) = mx
diff --git a/src/Data/Trie/Pred/Unified/Tail.hs b/src/Data/Trie/Pred/Unified/Tail.hs
--- a/src/Data/Trie/Pred/Unified/Tail.hs
+++ b/src/Data/Trie/Pred/Unified/Tail.hs
@@ -7,6 +7,7 @@
   , showTail
   , assignLit
   , lookup
+  , lookupWithL
   , lookupNearestParent
   , merge
   , areDisjoint
@@ -84,6 +85,19 @@
       [] -> ($ r) <$> mrx
       _  -> ($ r) <$> firstJust (map (lookup $ NE.fromList ts) xrs)
 
+lookupWithL :: Eq t => (t -> t) -> NonEmpty t -> UPTrie t x -> Maybe x
+lookupWithL f (t:|ts) (UMore t' mx xs)
+  | null ts = if f t == t'
+              then mx
+              else Nothing
+  | otherwise = if t == t'
+                then firstJust $ map (lookupWithL f $ NE.fromList ts) xs
+                else Nothing
+lookupWithL f (t:|ts) (UPred _ p mrx xrs) =
+  p t >>=
+    \r -> case ts of
+      [] -> ($ r) <$> mrx
+      _  -> ($ r) <$> firstJust (map (lookupWithL f $ NE.fromList ts) xrs)
 
 lookupNearestParent :: Eq t => NonEmpty t -> UPTrie t x -> Maybe x
 lookupNearestParent tss@(t:|ts) trie@(UMore t' mx xs) = case lookup tss trie of
@@ -140,4 +154,3 @@
     insert x@(UPred t _ _ _) (y@(UMore p _ _):rs)
       | t == p = insert x rs
       | otherwise = y : insert x rs
-