[project @ 2002-04-24 16:31:37 by simonmar]

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

diff --git a/Control/Monad/ST.hs b/Control/Monad/ST.hs
index 7817add..6d19b9c 100644 (file)
--- a/Control/Monad/ST.hs
+++ b/Control/Monad/ST.hs
@@ -1,14 +1,14 @@
 -----------------------------------------------------------------------------
--- 
+-- |
 -- 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
+-- Portability :  non-portable (requires universal quantification for runST)
 --
--- $Id: ST.hs,v 1.2 2001/06/29 09:41:37 simonmar Exp $
+-- $Id: ST.hs,v 1.6 2002/04/24 16:31:38 simonmar Exp $
 --
 -- The State Transformer Monad, ST
 --
@@ -29,17 +29,24 @@ module Control.Monad.ST
 
 import Prelude
 
+import Control.Monad.Fix
 import Data.Dynamic
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.ST
-import GHC.Prim                ( unsafeCoerce#, RealWorld )
+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