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diff --git a/Control/Monad/ST/Lazy.hs b/Control/Monad/ST/Lazy.hs
index 5144dcc..5bf1265 100644
--- a/Control/Monad/ST/Lazy.hs
+++ b/Control/Monad/ST/Lazy.hs
@@ -1,86 +1,72 @@
 -----------------------------------------------------------------------------
--- 
+-- |
 -- Module      :  Control.Monad.ST.Lazy
 -- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  provisional
 -- Portability :  non-portable (requires universal quantification for runST)
 --
--- $Id: Lazy.hs,v 1.2 2001/07/03 11:37:49 simonmar Exp $
---
--- This module presents an identical interface to Control.Monad.ST,
--- but the underlying implementation of the state thread is lazy.
+-- This module presents an identical interface to "Control.Monad.ST",
+-- except that the monad delays evaluation of state operations until
+-- a value depending on them is required.
 --
 -----------------------------------------------------------------------------
 
 module Control.Monad.ST.Lazy (
+	-- * The 'ST' monad
 	ST,
-
 	runST,
-	unsafeInterleaveST,
 	fixST,
 
-	STRef.STRef,
-	newSTRef, readSTRef, writeSTRef,
-
-	STArray.STArray,
-	newSTArray, readSTArray, writeSTArray, boundsSTArray, 
-	thawSTArray, freezeSTArray, unsafeFreezeSTArray, 
-#ifdef __GLASGOW_HASKELL__
--- no 'good' reason, just doesn't support it right now.
-        unsafeThawSTArray,
-#endif
+	-- * Converting between strict and lazy 'ST'
+	strictToLazyST, lazyToStrictST,
 
-	ST.unsafeIOToST, ST.stToIO,
+	-- * Converting 'ST' To 'IO'
+	RealWorld,
+	stToIO,
 
-	strictToLazyST, lazyToStrictST
+	-- * Unsafe operations
+	unsafeInterleaveST,
+	unsafeIOToST
     ) where
 
 import Prelude
 
-import qualified Data.STRef as STRef
-import Data.Array
+import Control.Monad.Fix
 
-#ifdef __GLASGOW_HASKELL__
+import Control.Monad.ST (RealWorld)
 import qualified Control.Monad.ST as ST
-import qualified GHC.Arr as STArray
+
+#ifdef __GLASGOW_HASKELL__
 import qualified GHC.ST
-import GHC.Base	( ($), ()(..) )
+import GHC.Base
 import Control.Monad
-import Data.Ix
-import GHC.Prim
 #endif
 
 #ifdef __HUGS__
-import qualified ST
-import Monad
-import Ix
-import Array
-import PrelPrim ( unST 
-		 , mkST 
-		 , PrimMutableArray
-		 , PrimArray
-		 , primNewArray
-		 , primReadArray
-		 , primWriteArray
-		 , primUnsafeFreezeArray
-		 , primSizeMutableArray
-		 , primSizeArray
-		 , primIndexArray
-		 )
+import Hugs.LazyST
 #endif
 
-
 #ifdef __GLASGOW_HASKELL__
+-- | The lazy state-transformer monad.
+-- A computation of type @'ST' s a@ transforms an internal state indexed
+-- by @s@, and returns a value of type @a@.
+-- The @s@ parameter is either
+--
+-- * an unstantiated type variable (inside invocations of 'runST'), or
+--
+-- * 'RealWorld' (inside invocations of 'stToIO').
+--
+-- It serves to keep the internal states of different invocations of
+-- 'runST' separate from each other and from invocations of 'stToIO'.
+--
+-- The '>>=' and '>>' operations are not strict in the state.  For example,
+--
+-- @'runST' (writeSTRef _|_ v >>= readSTRef _|_ >> return 2) = 2@
 newtype ST s a = ST (State s -> (a, State s))
 data State s = S# (State# s)
-#endif
-
-#ifdef __HUGS__
-newtype ST s a = ST (s -> (a,s))
-#endif
 
 instance Functor (ST s) where
     fmap f m = ST $ \ s ->
@@ -104,116 +90,37 @@ instance Monad (ST s) where
            in
            k_a new_s
 
-
-#ifdef __GLASGOW_HASKELL__
 {-# NOINLINE runST #-}
+-- | Return the value computed by a state transformer computation.
+-- The @forall@ ensures that the internal state used by the 'ST'
+-- computation is inaccessible to the rest of the program.
 runST :: (forall s. ST s a) -> a
 runST st = case st of ST the_st -> let (r,_) = the_st (S# realWorld#) in r
-#endif
-
-#ifdef __HUGS__
-runST :: (__forall s. ST s a) -> a
-runST st = case st of ST the_st -> let (r,_) = the_st realWorld in r
-	where realWorld = error "runST: entered the RealWorld"
-#endif
 
+-- | Allow the result of a state transformer computation to be used (lazily)
+-- inside the computation.
+-- Note that if @f@ is strict, @'fixST' f = _|_@.
 fixST :: (a -> ST s a) -> ST s a
 fixST m = ST (\ s -> 
 		let 
 		   ST m_r = m r
-		   (r,s)  = m_r s
+		   (r,s') = m_r s
 		in
-		   (r,s))
-
--- ---------------------------------------------------------------------------
--- Variables
-
-newSTRef   :: a -> ST s (STRef.STRef s a)
-readSTRef  :: STRef.STRef s a -> ST s a
-writeSTRef :: STRef.STRef s a -> a -> ST s ()
-
-newSTRef   = strictToLazyST . STRef.newSTRef
-readSTRef  = strictToLazyST . STRef.readSTRef
-writeSTRef r a = strictToLazyST (STRef.writeSTRef r a)
-
--- --------------------------------------------------------------------------
--- Arrays
-
-newSTArray 	    :: Ix ix => (ix,ix) -> elt -> ST s (STArray.STArray s ix elt)
-readSTArray   	    :: Ix ix => STArray.STArray s ix elt -> ix -> ST s elt 
-writeSTArray	    :: Ix ix => STArray.STArray s ix elt -> ix -> elt -> ST s () 
-boundsSTArray       :: Ix ix => STArray.STArray s ix elt -> (ix, ix)  
-thawSTArray 	    :: Ix ix => Array ix elt -> ST s (STArray.STArray s ix elt)
-freezeSTArray	    :: Ix ix => STArray.STArray s ix elt -> ST s (Array ix elt)
-unsafeFreezeSTArray :: Ix ix => STArray.STArray s ix elt -> ST s (Array ix elt)
-
-#ifdef __GLASGOW_HASKELL__
-
-newSTArray ixs init   	= strictToLazyST (STArray.newSTArray ixs init)
-
-readSTArray arr ix      = strictToLazyST (STArray.readSTArray arr ix)
-writeSTArray arr ix v   = strictToLazyST (STArray.writeSTArray arr ix v)
-boundsSTArray arr       = STArray.boundsSTArray arr
-thawSTArray arr	        = strictToLazyST (STArray.thawSTArray arr)
-freezeSTArray arr       = strictToLazyST (STArray.freezeSTArray arr)
-unsafeFreezeSTArray arr = strictToLazyST (STArray.unsafeFreezeSTArray arr)
-unsafeThawSTArray arr   = strictToLazyST (STArray.unsafeThawSTArray arr)
+		   (r,s'))
 #endif
 
-
-#ifdef __HUGS__
-newSTArray ixs elt = do
-  { arr <- strictToLazyST (primNewArray (rangeSize ixs) elt)
-  ; return (STArray ixs arr)
-  }
-
-boundsSTArray (STArray ixs arr)        = ixs
-readSTArray   (STArray ixs arr) ix     
-	= strictToLazyST (primReadArray arr (index ixs ix))
-writeSTArray  (STArray ixs arr) ix elt 
-	= strictToLazyST (primWriteArray arr (index ixs ix) elt)
-freezeSTArray (STArray ixs arr)        = do
-  { arr' <- strictToLazyST (primFreezeArray arr)
-  ; return (Array ixs arr')
-  }
-
-unsafeFreezeSTArray (STArray ixs arr)  = do 
-  { arr' <- strictToLazyST (primUnsafeFreezeArray arr)
-  ; return (Array ixs arr')
-  }
-
-thawSTArray (Array ixs arr) = do
-  { arr' <- strictToLazyST (primThawArray arr)
-  ; return (STArray ixs arr')
-  }
-
-primFreezeArray :: PrimMutableArray s a -> ST.ST s (PrimArray a)
-primFreezeArray arr = do
-  { let n = primSizeMutableArray arr
-  ; arr' <- primNewArray n arrEleBottom
-  ; mapM_ (copy arr arr') [0..n-1]
-  ; primUnsafeFreezeArray arr'
-  }
- where
-  copy arr arr' i = do { x <- primReadArray arr i; primWriteArray arr' i x }
-  arrEleBottom = error "primFreezeArray: panic"
-
-primThawArray :: PrimArray a -> ST.ST s (PrimMutableArray s a)
-primThawArray arr = do
-  { let n = primSizeArray arr
-  ; arr' <- primNewArray n arrEleBottom
-  ; mapM_ (copy arr arr') [0..n-1]
-  ; return arr'
-  }
- where
-  copy arr arr' i = primWriteArray arr' i (primIndexArray arr i)
-  arrEleBottom = error "primFreezeArray: panic"
-#endif
+instance MonadFix (ST s) where
+	mfix = fixST
 
 -- ---------------------------------------------------------------------------
 -- Strict <--> Lazy
 
 #ifdef __GLASGOW_HASKELL__
+{-|
+Convert a strict 'ST' computation into a lazy one.  The strict state
+thread passed to 'strictToLazyST' is not performed until the result of
+the lazy state thread it returns is demanded.
+-}
 strictToLazyST :: ST.ST s a -> ST s a
 strictToLazyST m = ST $ \s ->
         let 
@@ -223,25 +130,23 @@ strictToLazyST m = ST $ \s ->
 	in
 	(r, s')
 
+{-| 
+Convert a lazy 'ST' computation into a strict one.
+-}
 lazyToStrictST :: ST s a -> ST.ST s a
 lazyToStrictST (ST m) = GHC.ST.ST $ \s ->
         case (m (S# s)) of (a, S# s') -> (# s', a #)
-#endif
-
-#ifdef __HUGS__
-strictToLazyST :: ST.ST s a -> ST s a
-strictToLazyST m = ST $ \s ->
-        let 
-  	   pr = unST m s
-	   r  = fst pr
-	   s' = snd pr
-	in
-	(r, s')
-
-
-lazyToStrictST :: ST s a -> ST.ST s a
-lazyToStrictST (ST m) = mkST $ m
-#endif
 
 unsafeInterleaveST :: ST s a -> ST s a
 unsafeInterleaveST = strictToLazyST . ST.unsafeInterleaveST . lazyToStrictST
+#endif
+
+unsafeIOToST :: IO a -> ST s a
+unsafeIOToST = strictToLazyST . ST.unsafeIOToST
+
+-- | A monad transformer embedding lazy state transformers in the 'IO'
+-- monad.  The 'RealWorld' parameter indicates that the internal state
+-- used by the 'ST' computation is a special one supplied by the 'IO'
+-- monad, and thus distinct from those used by invocations of 'runST'.
+stToIO :: ST RealWorld a -> IO a
+stToIO = ST.stToIO . lazyToStrictST