[project @ 2003-09-08 16:23:57 by ross]

ST doc adjustments

diff --git a/Control/Monad/ST/Lazy.hs b/Control/Monad/ST/Lazy.hs
index b91e062..a160cdf 100644 (file)
--- a/Control/Monad/ST/Lazy.hs
+++ b/Control/Monad/ST/Lazy.hs
@@ -51,10 +51,16 @@ import Hugs.LazyST
 
 #ifdef __GLASGOW_HASKELL__
 -- | The lazy state-transformer monad.
--- The first parameter is used solely to keep the states of different
--- invocations of 'runST' separate from each other and from invocations
--- of 'Control.Monad.ST.stToIO'.  In the first case the type parameter
--- is not instantiated; in the second it is 'RealWorld'.
+-- 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'.
 newtype ST s a = ST (State s -> (a, State s))
 data State s = S# (State# s)
 
@@ -82,14 +88,14 @@ instance Monad (ST s) where
 
 {-# NOINLINE runST #-}
 -- | Return the value computed by a state transformer computation.
--- The @forall@ is a technical device to ensure that the state used
--- by the 'ST' computation is inaccessible to the rest of the program.
+-- 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
 
 -- | Allow the result of a state transformer computation to be used (lazily)
 -- inside the computation.
--- Note that if @f@ is strict, @'fixST' f@ will diverge.
+-- Note that if @f@ is strict, @'fixST' f = _|_@.
 fixST :: (a -> ST s a) -> ST s a
 fixST m = ST (\ s -> 
                let 
@@ -135,7 +141,8 @@ unsafeIOToST :: IO a -> ST s a
 unsafeIOToST = strictToLazyST . ST.unsafeIOToST
 
 -- | A monad transformer embedding lazy state transformers in the 'IO'
--- monad.  The 'RealWorld' parameter is a technical device to keep the
--- state used by such computations separate from those inside 'runST'.
+-- 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

diff --git a/GHC/Base.lhs b/GHC/Base.lhs
index 1d786bb..988c94e 100644 (file)
--- a/GHC/Base.lhs
+++ b/GHC/Base.lhs
@@ -994,8 +994,8 @@ unpackNBytes#  addr len# = unpack [] (len# -# 1#)
 
 #ifdef __HADDOCK__
 \begin{code}
--- | A placeholder argument for the 'Control.Monad.ST.ST' type constructor,
--- to mark a state embedded in the 'Prelude.IO' monad by
+-- | A special argument for the 'Control.Monad.ST.ST' type constructor,
+-- indexing a state embedded in the 'Prelude.IO' monad by
 -- 'Control.Monad.ST.stToIO'.
 data RealWorld
 \end{code}

diff --git a/GHC/IOBase.lhs b/GHC/IOBase.lhs
index b37fb1e..d5a997c 100644 (file)
--- a/GHC/IOBase.lhs
+++ b/GHC/IOBase.lhs
@@ -113,8 +113,9 @@ returnIO x = IO (\ s -> (# s, x #))
 -- Coercions between IO and ST
 
 -- | A monad transformer embedding strict state transformers in the 'IO'
--- monad.  The 'RealWorld' parameter is a technical device to keep the
--- state used by such computations separate from those inside 'runST'.
+-- 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 m) = IO m
 

diff --git a/GHC/ST.lhs b/GHC/ST.lhs
index 137debc..12ec5ca 100644 (file)
--- a/GHC/ST.lhs
+++ b/GHC/ST.lhs
@@ -34,10 +34,17 @@ too many people got bitten by space leaks when it was lazy.
 
 \begin{code}
 -- | The strict state-transformer monad.
--- The first parameter is used solely to keep the states of different
--- invocations of 'runST' separate from each other and from invocations
--- of 'Control.Monad.ST.stToIO'.  In the first case the type parameter
--- is not instantiated; in the second it is 'RealWorld'.
+-- 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 'Control.Monad.ST.stToIO').
+--
+-- It serves to keep the internal states of different invocations
+-- of 'runST' separate from each other and from invocations of
+-- 'Control.Monad.ST.stToIO'.
 newtype ST s a = ST (STRep s a)
 type STRep s a = State# s -> (# State# s, a #)
 
@@ -77,7 +84,7 @@ unsafeInterleaveST (ST m) = ST ( \ s ->
 
 -- | Allow the result of a state transformer computation to be used (lazily)
 -- inside the computation.
--- Note that if @f@ is strict, @'fixST' f@ will diverge.
+-- Note that if @f@ is strict, @'fixST' f = _|_@.
 fixST :: (a -> ST s a) -> ST s a
 fixST k = ST $ \ s ->
     let ans       = liftST (k r) s
@@ -129,8 +136,8 @@ All calls to @f@ will share a {\em single} array!  End SLPJ 95/04.
 -- module.  Regrettably delicate.  runST is behaving like a wrapper.
 
 -- | Return the value computed by a state transformer computation.
--- The @forall@ is a technical device to ensure that the state used
--- by the 'ST' computation is inaccessible to the rest of the program.
+-- 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 = runSTRep (case st of { ST st_rep -> st_rep })