monadplus 1.3 → 1.4

raw patch · 3 files changed

+92/−56 lines, 3 filesdep ~basePVP ok

version bump matches the API change (PVP)

Dependency ranges changed: base

API changes (from Hackage documentation)

Files

• monadplus.cabal +1/−1
• src/Control/Applicative/Alternative.hs +5/−26
• src/Control/Monad/Plus.hs +86/−29

@@ -1,6 +1,6 @@  name:               monadplus-version:            1.3+version:            1.4 cabal-version:      >= 1.10 author:             Hans Hoglund maintainer:         Hans Hoglund <hans@hanshoglund.se>

@@ -19,40 +19,18 @@ module Control.Applicative.Alternative (         -- * Basics         module Control.Applicative,-        asum,-        asum',      +        Foldable.asum,                  -- * Constructing         afold,         afromList,         afromMaybe,--        -- -- * Filtering-        -- afilter',-        -- apartition,-        -- -        -- -- ** Special filters-        -- ascatter,-        -- ascatter',-        -- acatMaybes,-        -- alefts,-        -- arights,-        -- apartitionEithers,-        -- -        -- -- * Special maps-        -- amapMaybe,-        -- aconcatMap,   ) where  import Control.Applicative-import Data.Foldable (Foldable(..), toList, asum)-import qualified Data.Foldable as Foldable+import Data.Foldable (Foldable(..)) --- |--- This generalizes the list-based 'concat' function. --- -asum' :: (Alternative f, Foldable t) => t (f a) -> f a-asum' = Foldable.asum+import qualified Data.Foldable as Foldable  -- |  -- Fold a value into an arbitrary 'MonadPlus' type.@@ -66,7 +44,7 @@ -- This function generalizes the 'listToMaybe' function. --  afromList :: Alternative f => [a] -> f a-afromList = asum . map pure+afromList = Foldable.asum . map pure  -- |  -- Translate maybe to an arbitrary 'Alternative' type.@@ -75,3 +53,4 @@ --  afromMaybe :: Alternative f => Maybe a -> f a afromMaybe = maybe empty pure +

@@ -1,4 +1,9 @@ +{-# LANGUAGE DeriveFunctor, DeriveFoldable, GeneralizedNewtypeDeriving,++    TypeSynonymInstances+    #-}+ ------------------------------------------------------------------------------------- -- | -- Copyright   : (c) Hans Hoglund 2012@@ -9,11 +14,13 @@ -- Stability   : experimental -- Portability : non-portable (TF,GNTD) ----- Partial maps and filters over 'MonadPlus' instances.+-- Partial maps and filters over 'MonadPlus' instances. The basic idea here is that+-- the monad interface together with the monoidal structure of 'MonadPlus' is enough+-- to implement partial maps and filters (i.e. 'mmapMaybe' and 'mfilter'). -- -- This is especially useful for sequential structures such as event lists, tracks etc. ----- Inspired by the Conal Elliott's blog post:+-- Inspired by the following blog post: -- --    * <http://conal.net/blog/posts/a-handy-generalized-filter> --@@ -22,7 +29,7 @@ module Control.Monad.Plus (         -- * Basics         module Control.Monad,-        msum,+        Monad.msum,         msum',                        -- * Constructing@@ -31,7 +38,7 @@         mfromMaybe,          -- * Filtering-        mfilter',+        -- mfilter,         mpartition,          -- ** Special filters@@ -45,13 +52,23 @@         -- * Special maps         mmapMaybe,         mconcatMap,+        +        -- * Utility+        Partial(..),+        partial,+        predicate,+        always,+        never,   ) where -import Control.Monad+import Control.Monad hiding (msum)+import Control.Applicative+import Data.Monoid import Data.List (partition)-import Data.Maybe (listToMaybe, maybeToList, catMaybes, mapMaybe)+import Data.Maybe (listToMaybe, maybeToList, catMaybes, mapMaybe, fromMaybe) import Data.Either (lefts, rights, partitionEithers) import Data.Foldable (Foldable(..), toList)+import qualified Control.Monad as Monad import qualified Data.Foldable as Foldable  -- |@@ -74,7 +91,7 @@ -- This function generalizes the 'listToMaybe' function. --  mfromList :: MonadPlus m => [a] -> m a-mfromList = msum . map return+mfromList = Monad.msum . map return  -- |  -- Translate maybe to an arbitrary 'MonadPlus' type.@@ -85,18 +102,6 @@ mfromMaybe = maybe mzero return  -- | --- 'mfilter'', applied to a predicate and a container, returns the container of--- those elements that satisfy the predicate; i.e.,------ > filter p xs = [ x | x <- xs, p x]------ This function generalizes the 'filter' function.--- (Identical to 'mfilter', it is just here for documentation purposes).--- -mfilter' :: MonadPlus m => (a -> Bool) -> m a -> m a-mfilter' = mfilter---- |  -- The 'partition' function takes a predicate a list and returns -- the pair of lists of elements which do and do not satisfy the -- predicate, respectively; i.e.,@@ -109,7 +114,7 @@ mpartition p a = (mfilter p a, mfilter (not . p) a)  -- | --- Pass through @Just@ occurrences.+-- Pass through @Just@ elements. --  -- This function generalizes the 'catMaybes' function. -- @@ -117,7 +122,7 @@ mcatMaybes = (>>= mfromMaybe)  -- | --- Pass through @Just@ occurrences.+-- Join list elements together. --  -- This function generalizes the 'catMaybes' function. -- @@ -125,15 +130,15 @@ mscatter = (>>= mfromList)  -- | --- Pass through @Just@ occurrences.+-- Join foldable elements together. --  -- This function generalizes the 'catMaybes' function. --  mscatter' :: (MonadPlus m, Foldable t) => m (t b) -> m b-mscatter' = (>>= mfromList . toList)+mscatter' = (>>= mfold)  -- | --- Pass through @Left@ occurrences.+-- Pass through @Left@ elements. --  -- This function generalizes the 'lefts' function. -- @@ -144,7 +149,7 @@         l (Right a) = Nothing  -- | --- Pass through @Right@ occurrences.+-- Pass through @Right@ elements. --  -- This function generalizes the 'rights' function. -- @@ -155,7 +160,7 @@         r (Right a) = Just a  -- | --- Separate @Left@ and @Right@ occurances.+-- Separate @Left@ and @Right@ elements. --  -- This function generalizes the 'partitionEithers' function. -- @@ -163,8 +168,6 @@ mpartitionEithers a = (mlefts a, mrights a)  -- -- |  -- Modify or discard a value. -- @@ -174,7 +177,7 @@ mmapMaybe f = mcatMaybes . liftM f  -- | --- Modify and return a number of values.+-- Modify, discard or spawn values. --  -- This function generalizes the 'concatMap' function. -- @@ -187,6 +190,60 @@  mmapRights :: MonadPlus m => (a -> Either c b) -> m a -> m b mmapRights f = mrights . liftM f+ -} +-- |+-- Convert a predicate to a partial function.+--+partial :: (a -> Bool) -> a -> Maybe a+partial p x = if p x then Just x else Nothing +-- |+-- Convert a partial function to a predicate.+--+predicate :: (a -> Maybe a) -> a -> Bool+predicate f x = case f x of+    Just _  -> True+    Nothing -> False++-- |+-- Convert a total function to a partial function.+--  +always :: (a -> b) -> a -> Maybe b+always f = Just . f++-- |+-- Make a partial function that always rejects its input.+--  +never :: a -> Maybe c+never = const Nothing++-- |+-- Wrapper for partial functions with 'MonadPlus' instance.+--+newtype Partial a b = Partial { getPartial :: a -> Maybe b }+    +instance Functor (Partial r) where+    fmap f (Partial g) = Partial (fmap f . g)++instance Monad (Partial r) where+    return x = Partial (\_ -> Just x)+    Partial f >>= k = Partial $ \r -> f r >>= \x -> getPartial (k x) r++instance MonadPlus (Partial r) where+    mzero = Partial (const Nothing)+    Partial f `mplus` Partial g = Partial $ \x -> f x `mplus` g x++instance Applicative (Partial r) where+    pure x = Partial (\_ -> Just x)+    Partial f <*> Partial g = Partial $ \x -> f x <*> g x++instance Alternative (Partial r) where+    empty = Partial (const Nothing)+    Partial f <|> Partial g = Partial $ \x -> f x <|> g x++instance Monoid (Partial a b) where+    mempty  = mzero+    mappend = mplus+