1 -----------------------------------------------------------------------------
3 -- Module : Control.Monad.ST
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable (requires universal quantification for runST)
11 -- This library provides support for /strict/ state threads, as
12 -- described in the PLDI \'94 paper by John Launchbury and Simon Peyton
13 -- Jones /Lazy Functional State Threads/.
15 -----------------------------------------------------------------------------
17 module Control.Monad.ST
20 ST, -- abstract, instance of Functor, Monad, Typeable.
21 runST, -- :: (forall s. ST s a) -> a
22 fixST, -- :: (a -> ST s a) -> ST s a
24 -- * Converting 'ST' to 'IO'
25 RealWorld, -- abstract
26 stToIO, -- :: ST RealWorld a -> IO a
28 -- * Unsafe operations
29 unsafeInterleaveST, -- :: ST s a -> ST s a
30 unsafeIOToST, -- :: IO a -> ST s a
31 unsafeSTToIO -- :: ST s a -> IO a
34 #if defined(__GLASGOW_HASKELL__)
35 import Control.Monad.Fix ()
37 import Control.Monad.Fix
42 #if defined(__GLASGOW_HASKELL__)
43 import GHC.ST ( ST, runST, fixST, unsafeInterleaveST )
44 import GHC.Base ( RealWorld )
45 import GHC.IO ( stToIO, unsafeIOToST, unsafeSTToIO )
46 #elif defined(__HUGS__)
49 import qualified Hugs.LazyST as LazyST
53 INSTANCE_TYPEABLE2(ST,sTTc,"ST")
54 INSTANCE_TYPEABLE0(RealWorld,realWorldTc,"RealWorld")
56 fixST :: (a -> ST s a) -> ST s a
57 fixST f = LazyST.lazyToStrictST (LazyST.fixST (LazyST.strictToLazyST . f))
59 unsafeInterleaveST :: ST s a -> ST s a
61 LazyST.lazyToStrictST . LazyST.unsafeInterleaveST . LazyST.strictToLazyST
64 #if !defined(__GLASGOW_HASKELL__)
65 instance MonadFix (ST s) where