[project @ 2005-02-02 14:54:18 by ross]

[ghc-base.git] / Control / Monad / ST.hs

diff --git a/Control/Monad/ST.hs b/Control/Monad/ST.hs
index 6d19b9c..0e34857 100644 (file)
--- a/Control/Monad/ST.hs
+++ b/Control/Monad/ST.hs
@@ -2,57 +2,62 @@
 -- |
 -- Module      :  Control.Monad.ST
 -- 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 (requires universal quantification for runST)
 --
--- $Id: ST.hs,v 1.6 2002/04/24 16:31:38 simonmar Exp $
---
--- 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)]