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|
-----------------------------------------------------------------------------
-- |
-- Module : Control.Monad.ST
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/core/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : non-portable (requires universal quantification for runST)
--
-- The State Transformer Monad, ST
--
-----------------------------------------------------------------------------
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
) 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 )
-- 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
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)]
|
