-----------------------------------------------------------------------------
---
+-- |
-- Module : Data.STRef
-- Copyright : (c) The University of Glasgow 2001
--- License : BSD-style (see the file libraries/core/LICENSE)
+-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable
---
--- $Id: STRef.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
+-- Portability : non-portable (requires non-portable module ST)
--
--- Mutable references in the ST monad.
+-- 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 ()
+ 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
+#endif
-#include "Dynamic.h"
+import Data.Typeable
+
+#include "Typeable.h"
INSTANCE_TYPEABLE2(STRef,stRefTc,"STRef")
+
+-- |Mutate the contents of an 'STRef'
+modifySTRef :: STRef s a -> (a -> a) -> ST s ()
+modifySTRef ref f = writeSTRef ref . f =<< readSTRef ref