+{-# LANGUAGE CPP #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : Data.STRef
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable (requires non-portable module ST)
+-- Portability : non-portable (uses Control.Monad.ST)
--
-- Mutable references in the (strict) ST monad.
--
-----------------------------------------------------------------------------
module Data.STRef (
- -- * STRefs
- STRef, -- abstract, instance Eq
- newSTRef, -- :: a -> ST s (STRef s a)
- readSTRef, -- :: STRef s a -> ST s a
- writeSTRef, -- :: STRef s a -> a -> ST s ()
- modifySTRef -- :: STRef s a -> (a -> a) -> ST s ()
+ -- * STRefs
+ STRef, -- abstract, instance Eq
+ newSTRef, -- :: a -> ST s (STRef s a)
+ readSTRef, -- :: STRef s a -> ST s a
+ writeSTRef, -- :: STRef s a -> a -> ST s ()
+ modifySTRef -- :: STRef s a -> (a -> a) -> ST s ()
) where
import Prelude
#ifdef __GLASGOW_HASKELL__
+import GHC.ST
import GHC.STRef
#endif
-import Data.Dynamic
+#ifdef __HUGS__
+import Hugs.ST
+import Data.Typeable
-#include "Dynamic.h"
+#include "Typeable.h"
INSTANCE_TYPEABLE2(STRef,stRefTc,"STRef")
+#endif
+
+-- |Mutate the contents of an 'STRef'
+modifySTRef :: STRef s a -> (a -> a) -> ST s ()
+modifySTRef ref f = writeSTRef ref . f =<< readSTRef ref