-- Stability : experimental
-- Portability : non-portable (requires universal quantification for runST)
--
--- The State Transformer Monad, ST
+-- This library provides support for /strict/ state threads, as
+-- described in the PLDI \'94 paper by John Launchbury and Simon Peyton
+-- Jones /Lazy State Threads/.
--
-----------------------------------------------------------------------------
module Control.Monad.ST
- (
- ST -- abstract, instance of Functor, Monad, Typeable.
- , runST -- :: (forall s. ST s a) -> a
- , fixST -- :: (a -> ST s a) -> ST s a
- , unsafeInterleaveST -- :: ST s a -> ST s a
-
- , unsafeIOToST -- :: IO a -> ST s a
-
- , RealWorld -- abstract
- , stToIO -- :: ST RealWorld a -> IO a
+ (
+ -- * The 'ST' Monad
+ ST, -- abstract, instance of Functor, Monad, Typeable.
+ runST, -- :: (forall s. ST s a) -> a
+ fixST, -- :: (a -> ST s a) -> ST s a
+
+ -- * Converting 'ST' to 'IO'
+ RealWorld, -- abstract
+ stToIO, -- :: ST RealWorld a -> IO a
+
+ -- * Unsafe operations
+ unsafeInterleaveST, -- :: ST s a -> ST s a
+ unsafeIOToST -- :: IO a -> ST s a
) where
import Prelude
import Control.Monad.Fix
-import Data.Dynamic
-#ifdef __GLASGOW_HASKELL__
-import GHC.ST
-import GHC.Base ( unsafeCoerce#, RealWorld )
-import GHC.IOBase ( IO(..), stToIO )
+#include "Typeable.h"
--- This relies on IO and ST having the same representation modulo the
--- constraint on the type of the state
---
-unsafeIOToST :: IO a -> ST s a
-unsafeIOToST (IO io) = ST $ \ s -> (unsafeCoerce# io) s
+#ifdef __HUGS__
+import Data.Typeable
+import Hugs.ST
+import qualified Hugs.LazyST as LazyST
+
+INSTANCE_TYPEABLE2(ST,sTTc,"ST")
+INSTANCE_TYPEABLE0(RealWorld,realWorldTc,"RealWorld")
+
+fixST :: (a -> ST s a) -> ST s a
+fixST f = LazyST.lazyToStrictST (LazyST.fixST (LazyST.strictToLazyST . f))
+
+unsafeInterleaveST :: ST s a -> ST s a
+unsafeInterleaveST =
+ LazyST.lazyToStrictST . LazyST.unsafeInterleaveST . LazyST.strictToLazyST
+#endif
+
+#ifdef __GLASGOW_HASKELL__
+import GHC.ST ( ST, runST, fixST, unsafeInterleaveST )
+import GHC.Base ( RealWorld )
+import GHC.IOBase ( stToIO, unsafeIOToST )
#endif
instance MonadFix (ST s) where
mfix = fixST
--- ---------------------------------------------------------------------------
--- Typeable instance
-
-sTTc :: TyCon
-sTTc = mkTyCon "ST"
-
-instance (Typeable a, Typeable b) => Typeable (ST a b) where
- typeOf st = mkAppTy sTTc [typeOf ((undefined :: ST a b -> a) st),
- typeOf ((undefined :: ST a b -> b) st)]