--
-- 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.
--
import Prelude
#ifdef __GLASGOW_HASKELL__
+import GHC.ST
import GHC.STRef
#endif
#ifdef __HUGS__
import Hugs.ST
-#endif
-
-import Data.Dynamic
+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