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|
-----------------------------------------------------------------------------
-- |
-- Module : Control.Monad.ST
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : non-portable (requires universal quantification for runST)
--
-- 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
(
-- * 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.Typeable
#include "Typeable.h"
#ifdef __HUGS__
import Hugs.ST
import qualified Hugs.LazyST as LazyST
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
import GHC.Base ( unsafeCoerce#, RealWorld )
import GHC.IOBase ( IO(..), stToIO )
-- 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
#endif
instance MonadFix (ST s) where
mfix = fixST
-- ---------------------------------------------------------------------------
-- Typeable instance
INSTANCE_TYPEABLE2(ST,sTTc,"ST")
|
