[project @ 2001-06-28 14:15:04 by simonmar]
[packages/pretty.git] / Control / Monad / ST.hs
1 -----------------------------------------------------------------------------
2 --
3 -- Module : Control.Monad.ST
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/core/LICENSE)
6 --
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable
10 --
11 -- $Id: ST.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
12 --
13 -- The State Transformer Monad, ST
14 --
15 -----------------------------------------------------------------------------
16
17 module Control.Monad.ST
18 (
19 ST -- abstract, instance of Functor, Monad, Typeable.
20 , runST -- :: (forall s. ST s a) -> a
21 , fixST -- :: (a -> ST s a) -> ST s a
22 , unsafeInterleaveST -- :: ST s a -> ST s a
23
24 , unsafeIOToST -- :: IO a -> ST s a
25
26 , RealWorld -- abstract
27 , stToIO -- :: ST RealWorld a -> IO a
28 ) where
29
30 import Prelude
31
32 import Data.Dynamic
33
34 #ifdef __GLASGOW_HASKELL__
35 import GHC.ST
36 import GHC.Prim ( unsafeCoerce#, RealWorld )
37 import GHC.IOBase ( IO(..), stToIO )
38
39 unsafeIOToST :: IO a -> ST s a
40 unsafeIOToST (IO io) = ST $ \ s ->
41 case ((unsafeCoerce# io) s) of
42 (# new_s, a #) -> unsafeCoerce# (STret new_s a)
43 #endif
44
45 -- ---------------------------------------------------------------------------
46 -- Typeable instance
47
48 sTTc :: TyCon
49 sTTc = mkTyCon "ST"
50
51 instance (Typeable a, Typeable b) => Typeable (ST a b) where
52 typeOf st = mkAppTy sTTc [typeOf ((undefined :: ST a b -> a) st),
53 typeOf ((undefined :: ST a b -> b) st)]