X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FFoldable.hs;h=354bd8b270a655fe565fa5884b80e48280b8b4f7;hb=7a97ec4b12e1fbec5505f82032cf4dc435b5a60c;hp=7c34b77f64ae5dfb7cc7ed2a48b203778d979b17;hpb=afe7ed8026edd943550b05f4895c99601207fea5;p=ghc-base.git

diff --git a/Data/Foldable.hs b/Data/Foldable.hs
index 7c34b77..354bd8b 100644
--- a/Data/Foldable.hs
+++ b/Data/Foldable.hs
@@ -1,10 +1,12 @@
+{-# LANGUAGE CPP #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Foldable
 -- Copyright   :  Ross Paterson 2005
 -- License     :  BSD-style (see the LICENSE file in the distribution)
 --
--- Maintainer  :  ross@soi.city.ac.uk
+-- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
 -- Portability :  portable
 --
@@ -17,59 +19,69 @@
 -- for this module.
 
 module Data.Foldable (
-	-- * Folds
-	Foldable(..),
-	-- ** Special biased folds
-	foldr',
-	foldl',
-	foldrM,
-	foldlM,
-	-- ** Folding actions
-	-- *** Applicative actions
-	traverse_,
-	for_,
-	sequenceA_,
-	asum,
-	-- *** Monadic actions
-	mapM_,
-	forM_,
-	sequence_,
-	msum,
-	-- ** Specialized folds
-	toList,
-	concat,
-	concatMap,
-	and,
-	or,
-	any,
-	all,
-	sum,
-	product,
-	maximum,
-	maximumBy,
-	minimum,
-	minimumBy,
-	-- ** Searches
-	elem,
-	notElem,
-	find
-	) where
+    -- * Folds
+    Foldable(..),
+    -- ** Special biased folds
+    foldr',
+    foldl',
+    foldrM,
+    foldlM,
+    -- ** Folding actions
+    -- *** Applicative actions
+    traverse_,
+    for_,
+    sequenceA_,
+    asum,
+    -- *** Monadic actions
+    mapM_,
+    forM_,
+    sequence_,
+    msum,
+    -- ** Specialized folds
+    toList,
+    concat,
+    concatMap,
+    and,
+    or,
+    any,
+    all,
+    sum,
+    product,
+    maximum,
+    maximumBy,
+    minimum,
+    minimumBy,
+    -- ** Searches
+    elem,
+    notElem,
+    find
+    ) where
 
 import Prelude hiding (foldl, foldr, foldl1, foldr1, mapM_, sequence_,
-		elem, notElem, concat, concatMap, and, or, any, all,
-		sum, product, maximum, minimum)
+                elem, notElem, concat, concatMap, and, or, any, all,
+                sum, product, maximum, minimum)
 import qualified Prelude (foldl, foldr, foldl1, foldr1)
-import Control.Arrow (ArrowZero(..))
 import Control.Applicative
 import Control.Monad (MonadPlus(..))
 import Data.Maybe (fromMaybe, listToMaybe)
 import Data.Monoid
-import Data.Array
+
+#ifdef __NHC__
+import Control.Arrow (ArrowZero(..)) -- work around nhc98 typechecker problem
+#endif
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Exts (build)
 #endif
 
+#if defined(__GLASGOW_HASKELL__)
+import GHC.Arr
+#elif defined(__HUGS__)
+import Hugs.Array
+#elif defined(__NHC__)
+import Array
+#endif
+
 -- | Data structures that can be folded.
 --
 -- Minimal complete definition: 'foldMap' or 'foldr'.
@@ -80,96 +92,106 @@ import GHC.Exts (build)
 --
 -- a suitable instance would be
 --
--- > instance Foldable Tree
+-- > instance Foldable Tree where
 -- >    foldMap f Empty = mempty
 -- >    foldMap f (Leaf x) = f x
 -- >    foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r
 --
 -- This is suitable even for abstract types, as the monoid is assumed
--- to satisfy the monoid laws.
+-- to satisfy the monoid laws.  Alternatively, one could define @foldr@:
+--
+-- > instance Foldable Tree where
+-- >    foldr f z Empty = z
+-- >    foldr f z (Leaf x) = f x z
+-- >    foldr f z (Node l k r) = foldr f (f k (foldr f z r)) l
 --
 class Foldable t where
-	-- | Combine the elements of a structure using a monoid.
-	fold :: Monoid m => t m -> m
-	fold = foldMap id
-
-	-- | Map each element of the structure to a monoid,
-	-- and combine the results.
-	foldMap :: Monoid m => (a -> m) -> t a -> m
-	foldMap f = foldr (mappend . f) mempty
-
-	-- | Right-associative fold of a structure.
-	--
-	-- @'foldr' f z = 'Prelude.foldr' f z . 'toList'@
-	foldr :: (a -> b -> b) -> b -> t a -> b
-	foldr f z t = appEndo (foldMap (Endo . f) t) z
-
-	-- | Left-associative fold of a structure.
-	--
-	-- @'foldl' f z = 'Prelude.foldl' f z . 'toList'@
-	foldl :: (a -> b -> a) -> a -> t b -> a
-	foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z
-
-	-- | A variant of 'foldr' that has no base case,
-	-- and thus may only be applied to non-empty structures.
-	--
-	-- @'foldr1' f = 'Prelude.foldr1' f . 'toList'@
-	foldr1 :: (a -> a -> a) -> t a -> a
-	foldr1 f xs = fromMaybe (error "foldr1: empty structure")
-			(foldr mf Nothing xs)
-	  where mf x Nothing = Just x
-		mf x (Just y) = Just (f x y)
-
-	-- | A variant of 'foldl' that has no base case,
-	-- and thus may only be applied to non-empty structures.
-	--
-	-- @'foldl1' f = 'Prelude.foldl1' f . 'toList'@
-	foldl1 :: (a -> a -> a) -> t a -> a
-	foldl1 f xs = fromMaybe (error "foldl1: empty structure")
-			(foldl mf Nothing xs)
-	  where mf Nothing y = Just y
-		mf (Just x) y = Just (f x y)
+    -- | Combine the elements of a structure using a monoid.
+    fold :: Monoid m => t m -> m
+    fold = foldMap id
+
+    -- | Map each element of the structure to a monoid,
+    -- and combine the results.
+    foldMap :: Monoid m => (a -> m) -> t a -> m
+    foldMap f = foldr (mappend . f) mempty
+
+    -- | Right-associative fold of a structure.
+    --
+    -- @'foldr' f z = 'Prelude.foldr' f z . 'toList'@
+    foldr :: (a -> b -> b) -> b -> t a -> b
+    foldr f z t = appEndo (foldMap (Endo . f) t) z
+
+    -- | Left-associative fold of a structure.
+    --
+    -- @'foldl' f z = 'Prelude.foldl' f z . 'toList'@
+    foldl :: (a -> b -> a) -> a -> t b -> a
+    foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z
+
+    -- | A variant of 'foldr' that has no base case,
+    -- and thus may only be applied to non-empty structures.
+    --
+    -- @'foldr1' f = 'Prelude.foldr1' f . 'toList'@
+    foldr1 :: (a -> a -> a) -> t a -> a
+    foldr1 f xs = fromMaybe (error "foldr1: empty structure")
+                    (foldr mf Nothing xs)
+      where
+        mf x Nothing = Just x
+        mf x (Just y) = Just (f x y)
+
+    -- | A variant of 'foldl' that has no base case,
+    -- and thus may only be applied to non-empty structures.
+    --
+    -- @'foldl1' f = 'Prelude.foldl1' f . 'toList'@
+    foldl1 :: (a -> a -> a) -> t a -> a
+    foldl1 f xs = fromMaybe (error "foldl1: empty structure")
+                    (foldl mf Nothing xs)
+      where
+        mf Nothing y = Just y
+        mf (Just x) y = Just (f x y)
 
 -- instances for Prelude types
 
 instance Foldable Maybe where
-	foldr f z Nothing = z
-	foldr f z (Just x) = f x z
+    foldr _ z Nothing = z
+    foldr f z (Just x) = f x z
 
-	foldl f z Nothing = z
-	foldl f z (Just x) = f z x
+    foldl _ z Nothing = z
+    foldl f z (Just x) = f z x
 
 instance Foldable [] where
-	foldr = Prelude.foldr
-	foldl = Prelude.foldl
-	foldr1 = Prelude.foldr1
-	foldl1 = Prelude.foldl1
+    foldr = Prelude.foldr
+    foldl = Prelude.foldl
+    foldr1 = Prelude.foldr1
+    foldl1 = Prelude.foldl1
 
 instance Ix i => Foldable (Array i) where
-	foldr f z = Prelude.foldr f z . elems
+    foldr f z = Prelude.foldr f z . elems
+    foldl f z = Prelude.foldl f z . elems
+    foldr1 f = Prelude.foldr1 f . elems
+    foldl1 f = Prelude.foldl1 f . elems
 
 -- | Fold over the elements of a structure,
 -- associating to the right, but strictly.
 foldr' :: Foldable t => (a -> b -> b) -> b -> t a -> b
-foldr' f z xs = foldl f' id xs z
+foldr' f z0 xs = foldl f' id xs z0
   where f' k x z = k $! f x z
 
 -- | Monadic fold over the elements of a structure,
 -- associating to the right, i.e. from right to left.
 foldrM :: (Foldable t, Monad m) => (a -> b -> m b) -> b -> t a -> m b
-foldrM f z xs = foldl f' return xs z
+foldrM f z0 xs = foldl f' return xs z0
   where f' k x z = f x z >>= k
 
 -- | Fold over the elements of a structure,
 -- associating to the left, but strictly.
 foldl' :: Foldable t => (a -> b -> a) -> a -> t b -> a
-foldl' f z xs = foldr f' id xs z
+foldl' f z0 xs = foldr f' id xs z0
   where f' x k z = k $! f z x
 
 -- | Monadic fold over the elements of a structure,
 -- associating to the left, i.e. from left to right.
 foldlM :: (Foldable t, Monad m) => (a -> b -> m a) -> a -> t b -> m a
-foldlM f z xs = foldr f' return xs z
+foldlM f z0 xs = foldr f' return xs z0
   where f' x k z = f z x >>= k
 
 -- | Map each element of a structure to an action, evaluate
@@ -182,7 +204,7 @@ for_ :: (Foldable t, Applicative f) => t a -> (a -> f b) -> f ()
 {-# INLINE for_ #-}
 for_ = flip traverse_
 
--- | Map each element of a structure to an monadic action, evaluate
+-- | Map each element of a structure to a monadic action, evaluate
 -- these actions from left to right, and ignore the results.
 mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()
 mapM_ f = foldr ((>>) . f) (return ())
@@ -216,6 +238,7 @@ msum = foldr mplus mzero
 
 -- | List of elements of a structure.
 toList :: Foldable t => t a -> [a]
+{-# INLINE toList #-}
 #ifdef __GLASGOW_HASKELL__
 toList t = build (\ c n -> foldr c n t)
 #else
@@ -268,8 +291,8 @@ maximum = foldr1 max
 maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
 maximumBy cmp = foldr1 max'
   where max' x y = case cmp x y of
-			GT -> x
-			_  -> y
+                        GT -> x
+                        _  -> y
 
 -- | The least element of a non-empty structure.
 minimum :: (Foldable t, Ord a) => t a -> a
@@ -280,8 +303,8 @@ minimum = foldr1 min
 minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
 minimumBy cmp = foldr1 min'
   where min' x y = case cmp x y of
-			GT -> y
-			_  -> x
+                        GT -> y
+                        _  -> x
 
 -- | Does the element occur in the structure?
 elem :: (Foldable t, Eq a) => a -> t a -> Bool