Fix Windows-only warnings

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

diff --git a/Control/Monad/ST/Lazy.hs b/Control/Monad/ST/Lazy.hs
index a160cdf..00aa4f0 100644 (file)
--- a/Control/Monad/ST/Lazy.hs
+++ b/Control/Monad/ST/Lazy.hs
@@ -9,27 +9,27 @@
 -- Portability :  non-portable (requires universal quantification for runST)
 --
 -- This module presents an identical interface to "Control.Monad.ST",
--- but the underlying implementation of the state thread is /lazy/ (in
--- the sense that (@_|_ >> a@ is not necessarily equal to @_|_@).
+-- 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,
-       fixST,
+        -- * The 'ST' monad
+        ST,
+        runST,
+        fixST,
 
-       -- * Converting between strict and lazy 'ST'
-       strictToLazyST, lazyToStrictST,
+        -- * Converting between strict and lazy 'ST'
+        strictToLazyST, lazyToStrictST,
 
-       -- * Converting 'ST' To 'IO'
-       RealWorld,
-       stToIO,
+        -- * Converting 'ST' To 'IO'
+        RealWorld,
+        stToIO,
 
-       -- * Unsafe operations
-       unsafeInterleaveST,
-       unsafeIOToST
+        -- * Unsafe operations
+        unsafeInterleaveST,
+        unsafeIOToST
     ) where
 
 import Prelude
@@ -61,6 +61,10 @@ import Hugs.LazyST
 --
 -- 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)
 
@@ -76,7 +80,7 @@ instance Monad (ST s) where
 
         return a = ST $ \ s -> (a,s)
         m >> k   =  m >>= \ _ -> k
-       fail s   = error s
+        fail s   = error s
 
         (ST m) >>= k
          = ST $ \ s ->
@@ -98,15 +102,15 @@ runST st = case st of ST the_st -> let (r,_) = the_st (S# realWorld#) in r
 -- 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
-               in
-                  (r,s'))
+                let 
+                   ST m_r = m r
+                   (r,s') = m_r s
+                in
+                   (r,s'))
 #endif
 
 instance MonadFix (ST s) where
-       mfix = fixST
+        mfix = fixST
 
 -- ---------------------------------------------------------------------------
 -- Strict <--> Lazy
@@ -120,11 +124,11 @@ the lazy state thread it returns is demanded.
 strictToLazyST :: ST.ST s a -> ST s a
 strictToLazyST m = ST $ \s ->
         let 
-          pr = case s of { S# s# -> GHC.ST.liftST m s# }
-          r  = case pr of { GHC.ST.STret _ v -> v }
-          s' = case pr of { GHC.ST.STret s2# _ -> S# s2# }
-       in
-       (r, s')
+           pr = case s of { S# s# -> GHC.ST.liftST m s# }
+           r  = case pr of { GHC.ST.STret _ v -> v }
+           s' = case pr of { GHC.ST.STret s2# _ -> S# s2# }
+        in
+        (r, s')
 
 {-| 
 Convert a lazy 'ST' computation into a strict one.