X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Control%2FApplicative.hs;h=c38e5809d9c75b7e71b64ac96dd169e3657bbca6;hb=41e8fba828acbae1751628af50849f5352b27873;hp=8aa86e116480d8355bbb44015dfe060bf3184683;hpb=7e9f8a1fd3b8290341605eb0530d0dd47c70479b;p=ghc-base.git

diff --git a/Control/Applicative.hs b/Control/Applicative.hs
index 8aa86e1..c38e580 100644
--- a/Control/Applicative.hs
+++ b/Control/Applicative.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Applicative
@@ -23,29 +25,35 @@
 -- 'Data.Traversable.Traversable' class.
 
 module Control.Applicative (
-        -- * Applicative functors
-        Applicative(..),
-        -- * Alternatives
-        Alternative(..),
-        -- * Instances
-        Const(..), WrappedMonad(..), WrappedArrow(..), ZipList(..),
-        -- * Utility functions
-        (<$>), (<$), (<**>),
-        liftA, liftA2, liftA3,
-        optional,
-        ) where
+    -- * Applicative functors
+    Applicative(..),
+    -- * Alternatives
+    Alternative(..),
+    -- * Instances
+    Const(..), WrappedMonad(..), WrappedArrow(..), ZipList(..),
+    -- * Utility functions
+    (<$>), (<$), (<**>),
+    liftA, liftA2, liftA3,
+    optional,
+    ) where
 
 import Prelude hiding (id,(.))
-import qualified Prelude (id)
 
 import Control.Category
-import Control.Arrow
-        (Arrow(arr, (&&&)), ArrowZero(zeroArrow), ArrowPlus((<+>)))
+import Control.Arrow (Arrow(arr, (&&&)), ArrowZero(zeroArrow), ArrowPlus((<+>)))
 import Control.Monad (liftM, ap, MonadPlus(..))
 import Control.Monad.Instances ()
+#ifndef __NHC__
+import Control.Monad.ST (ST)
+import qualified Control.Monad.ST.Lazy as Lazy (ST)
+#endif
 import Data.Functor ((<$>), (<$))
 import Data.Monoid (Monoid(..))
 
+#ifdef __GLASGOW_HASKELL__
+import GHC.Conc (STM, retry, orElse)
+#endif
+
 infixl 3 <|>
 infixl 4 <*>, <*, *>, <**>
 
@@ -82,19 +90,19 @@ infixl 4 <*>, <*, *>, <**>
 -- Minimal complete definition: 'pure' and '<*>'.
 
 class Functor f => Applicative f where
-        -- | Lift a value.
-        pure :: a -> f a
+    -- | Lift a value.
+    pure :: a -> f a
 
-        -- | Sequential application.
-        (<*>) :: f (a -> b) -> f a -> f b
+    -- | Sequential application.
+    (<*>) :: f (a -> b) -> f a -> f b
 
-	-- | Sequence actions, discarding the value of the first argument.
-	(*>) :: f a -> f b -> f b
-	(*>) = liftA2 (const id)
+    -- | Sequence actions, discarding the value of the first argument.
+    (*>) :: f a -> f b -> f b
+    (*>) = liftA2 (const id)
 
-	-- | Sequence actions, discarding the value of the second argument.
-	(<*) :: f a -> f b -> f a
-	(<*) = liftA2 const
+    -- | Sequence actions, discarding the value of the second argument.
+    (<*) :: f a -> f b -> f a
+    (<*) = liftA2 const
 
 -- | A monoid on applicative functors.
 --
@@ -106,90 +114,117 @@ class Functor f => Applicative f where
 --
 -- * @many v = some v '<|>' 'pure' []@
 class Applicative f => Alternative f where
-        -- | The identity of '<|>'
-        empty :: f a
-        -- | An associative binary operation
-        (<|>) :: f a -> f a -> f a
-
-	-- | One or more.
-	some :: f a -> f [a]
-	some v = some_v
-	  where many_v = some_v <|> pure []
-		some_v = (:) <$> v <*> many_v
-
-	-- | Zero or more.
-	many :: f a -> f [a]
-	many v = many_v
-	  where many_v = some_v <|> pure []
-		some_v = (:) <$> v <*> many_v
+    -- | The identity of '<|>'
+    empty :: f a
+    -- | An associative binary operation
+    (<|>) :: f a -> f a -> f a
+
+    -- | One or more.
+    some :: f a -> f [a]
+    some v = some_v
+      where
+        many_v = some_v <|> pure []
+        some_v = (:) <$> v <*> many_v
+
+    -- | Zero or more.
+    many :: f a -> f [a]
+    many v = many_v
+      where
+        many_v = some_v <|> pure []
+        some_v = (:) <$> v <*> many_v
 
 -- instances for Prelude types
 
 instance Applicative Maybe where
-        pure = return
-        (<*>) = ap
+    pure = return
+    (<*>) = ap
 
 instance Alternative Maybe where
-        empty = Nothing
-        Nothing <|> p = p
-        Just x <|> _ = Just x
+    empty = Nothing
+    Nothing <|> p = p
+    Just x <|> _ = Just x
 
 instance Applicative [] where
-        pure = return
-        (<*>) = ap
+    pure = return
+    (<*>) = ap
 
 instance Alternative [] where
-        empty = []
-        (<|>) = (++)
+    empty = []
+    (<|>) = (++)
 
 instance Applicative IO where
-        pure = return
-        (<*>) = ap
+    pure = return
+    (<*>) = ap
+
+#ifndef __NHC__
+instance Applicative (ST s) where
+    pure = return
+    (<*>) = ap
+
+instance Applicative (Lazy.ST s) where
+    pure = return
+    (<*>) = ap
+#endif
+
+#ifdef __GLASGOW_HASKELL__
+instance Applicative STM where
+    pure = return
+    (<*>) = ap
+
+instance Alternative STM where
+    empty = retry
+    (<|>) = orElse
+#endif
 
 instance Applicative ((->) a) where
-        pure = const
-        (<*>) f g x = f x (g x)
+    pure = const
+    (<*>) f g x = f x (g x)
 
 instance Monoid a => Applicative ((,) a) where
-        pure x = (mempty, x)
-        (u, f) <*> (v, x) = (u `mappend` v, f x)
+    pure x = (mempty, x)
+    (u, f) <*> (v, x) = (u `mappend` v, f x)
+
+instance Applicative (Either e) where
+    pure          = Right
+    Left  e <*> _ = Left e
+    Right f <*> r = fmap f r
 
 -- new instances
 
 newtype Const a b = Const { getConst :: a }
 
 instance Functor (Const m) where
-        fmap _ (Const v) = Const v
+    fmap _ (Const v) = Const v
 
 instance Monoid m => Applicative (Const m) where
-        pure _ = Const mempty
-        Const f <*> Const v = Const (f `mappend` v)
+    pure _ = Const mempty
+    Const f <*> Const v = Const (f `mappend` v)
 
 newtype WrappedMonad m a = WrapMonad { unwrapMonad :: m a }
 
 instance Monad m => Functor (WrappedMonad m) where
-        fmap f (WrapMonad v) = WrapMonad (liftM f v)
+    fmap f (WrapMonad v) = WrapMonad (liftM f v)
 
 instance Monad m => Applicative (WrappedMonad m) where
-        pure = WrapMonad . return
-        WrapMonad f <*> WrapMonad v = WrapMonad (f `ap` v)
+    pure = WrapMonad . return
+    WrapMonad f <*> WrapMonad v = WrapMonad (f `ap` v)
 
 instance MonadPlus m => Alternative (WrappedMonad m) where
-        empty = WrapMonad mzero
-        WrapMonad u <|> WrapMonad v = WrapMonad (u `mplus` v)
+    empty = WrapMonad mzero
+    WrapMonad u <|> WrapMonad v = WrapMonad (u `mplus` v)
 
 newtype WrappedArrow a b c = WrapArrow { unwrapArrow :: a b c }
 
 instance Arrow a => Functor (WrappedArrow a b) where
-        fmap f (WrapArrow a) = WrapArrow (a >>> arr f)
+    fmap f (WrapArrow a) = WrapArrow (a >>> arr f)
 
 instance Arrow a => Applicative (WrappedArrow a b) where
-        pure x = WrapArrow (arr (const x))
-        WrapArrow f <*> WrapArrow v = WrapArrow (f &&& v >>> arr (uncurry id))
+    pure x = WrapArrow (arr (const x))
+    WrapArrow f <*> WrapArrow v = WrapArrow (f &&& v >>> arr (uncurry id))
 
 instance (ArrowZero a, ArrowPlus a) => Alternative (WrappedArrow a b) where
-        empty = WrapArrow zeroArrow
-        WrapArrow u <|> WrapArrow v = WrapArrow (u <+> v)
+    empty = WrapArrow zeroArrow
+    WrapArrow u <|> WrapArrow v = WrapArrow (u <+> v)
 
 -- | Lists, but with an 'Applicative' functor based on zipping, so that
 --
@@ -198,11 +233,11 @@ instance (ArrowZero a, ArrowPlus a) => Alternative (WrappedArrow a b) where
 newtype ZipList a = ZipList { getZipList :: [a] }
 
 instance Functor ZipList where
-        fmap f (ZipList xs) = ZipList (map f xs)
+    fmap f (ZipList xs) = ZipList (map f xs)
 
 instance Applicative ZipList where
-        pure x = ZipList (repeat x)
-        ZipList fs <*> ZipList xs = ZipList (zipWith id fs xs)
+    pure x = ZipList (repeat x)
+    ZipList fs <*> ZipList xs = ZipList (zipWith id fs xs)
 
 -- extra functions