[project @ 2003-09-05 17:36:40 by ross]

minimal docs

diff --git a/Control/Monad/ST.hs b/Control/Monad/ST.hs
index 3ea3bb3..705787e 100644 (file)
--- a/Control/Monad/ST.hs
+++ b/Control/Monad/ST.hs
@@ -21,13 +21,13 @@ module Control.Monad.ST
        runST,          -- :: (forall s. ST s a) -> a
        fixST,          -- :: (a -> ST s a) -> ST s a
 
-       -- * Unsafe operations
-       unsafeInterleaveST,     -- :: ST s a -> ST s a
-       unsafeIOToST,           -- :: IO a -> ST s a
-
        -- * Converting 'ST' to 'IO'
        RealWorld,              -- abstract
-       stToIO                  -- :: ST RealWorld a -> IO a
+       stToIO,                 -- :: ST RealWorld a -> IO a
+
+       -- * Unsafe operations
+       unsafeInterleaveST,     -- :: ST s a -> ST s a
+       unsafeIOToST            -- :: IO a -> ST s a
       ) where
 
 import Prelude

diff --git a/Control/Monad/ST/Lazy.hs b/Control/Monad/ST/Lazy.hs
index 413659e..b91e062 100644 (file)
--- a/Control/Monad/ST/Lazy.hs
+++ b/Control/Monad/ST/Lazy.hs
@@ -20,16 +20,16 @@ module Control.Monad.ST.Lazy (
        runST,
        fixST,
 
-       -- * Unsafe operations
-       unsafeInterleaveST,
-       unsafeIOToST,
+       -- * Converting between strict and lazy 'ST'
+       strictToLazyST, lazyToStrictST,
 
        -- * Converting 'ST' To 'IO'
        RealWorld,
        stToIO,
 
-       -- * Converting between strict and lazy 'ST'
-       strictToLazyST, lazyToStrictST
+       -- * Unsafe operations
+       unsafeInterleaveST,
+       unsafeIOToST
     ) where
 
 import Prelude
@@ -50,6 +50,11 @@ import Hugs.LazyST
 #endif
 
 #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'.
 newtype ST s a = ST (State s -> (a, State s))
 data State s = S# (State# s)
 
@@ -76,9 +81,15 @@ instance Monad (ST s) where
            k_a new_s
 
 {-# 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.
 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.
 fixST :: (a -> ST s a) -> ST s a
 fixST m = ST (\ s -> 
                let 
@@ -123,5 +134,8 @@ unsafeInterleaveST = strictToLazyST . ST.unsafeInterleaveST . lazyToStrictST
 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'.
 stToIO :: ST RealWorld a -> IO a
 stToIO = ST.stToIO . lazyToStrictST

diff --git a/GHC/Base.lhs b/GHC/Base.lhs
index f957a6d..1d786bb 100644 (file)
--- a/GHC/Base.lhs
+++ b/GHC/Base.lhs
@@ -991,3 +991,12 @@ unpackNBytes#  addr len# = unpack [] (len# -# 1#)
 
   #-}
 \end{code}
+
+#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
+-- 'Control.Monad.ST.stToIO'.
+data RealWorld
+\end{code}
+#endif

diff --git a/GHC/IOBase.lhs b/GHC/IOBase.lhs
index be727df..b37fb1e 100644 (file)
--- a/GHC/IOBase.lhs
+++ b/GHC/IOBase.lhs
@@ -112,7 +112,9 @@ returnIO x = IO (\ s -> (# s, x #))
 -- ---------------------------------------------------------------------------
 -- Coercions between IO and ST
 
---stToIO        :: (forall s. ST s a) -> IO a
+-- | 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'.
 stToIO       :: ST RealWorld a -> IO a
 stToIO (ST m) = IO m
 

diff --git a/GHC/ST.lhs b/GHC/ST.lhs
index 65bf835..137debc 100644 (file)
--- a/GHC/ST.lhs
+++ b/GHC/ST.lhs
@@ -33,6 +33,11 @@ The state-transformer monad proper.  By default the monad is strict;
 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'.
 newtype ST s a = ST (STRep s a)
 type STRep s a = State# s -> (# State# s, a #)
 
@@ -70,6 +75,9 @@ unsafeInterleaveST (ST m) = ST ( \ s ->
     (# s, 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.
 fixST :: (a -> ST s a) -> ST s a
 fixST k = ST $ \ s ->
     let ans       = liftST (k r) s
@@ -119,6 +127,10 @@ All calls to @f@ will share a {\em single} array!  End SLPJ 95/04.
 -- The INLINE prevents runSTRep getting inlined in *this* module
 -- so that it is still visible when runST is inlined in an importing
 -- 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.
 runST :: (forall s. ST s a) -> a
 runST st = runSTRep (case st of { ST st_rep -> st_rep })