[project @ 2001-08-04 06:19:54 by ken]

[ghc-hetmet.git] / ghc / lib / std / PrelST.lhs

diff --git a/ghc/lib/std/PrelST.lhs b/ghc/lib/std/PrelST.lhs
index 916bc66..9efa299 100644 (file)
--- a/ghc/lib/std/PrelST.lhs
+++ b/ghc/lib/std/PrelST.lhs
@@ -1,6 +1,9 @@
+% ------------------------------------------------------------------------------
+% $Id: PrelST.lhs,v 1.20 2001/02/22 16:48:24 qrczak Exp $
 %
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The University of Glasgow, 1992-2000
 %
+
 \section[PrelST]{The @ST@ monad}
 
 \begin{code}
@@ -8,9 +11,11 @@
 
 module PrelST where
 
-import Monad
 import PrelBase
-import PrelGHC
+import PrelShow
+import PrelNum
+
+default ()
 \end{code}
 
 %*********************************************************
@@ -23,10 +28,11 @@ 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}
-newtype ST s a = ST (State# s -> (# State# s, a #))
+newtype ST s a = ST (STRep s a)
+type STRep s a = State# s -> (# State# s, a #)
 
 instance Functor (ST s) where
-    map f (ST m) = ST $ \ s ->
+    fmap f (ST m) = ST $ \ s ->
       case (m s) of { (# new_s, r #) ->
       (# new_s, f r #) }
 
@@ -50,13 +56,6 @@ data STret s a = STret (State# s) a
 liftST :: ST s a -> State# s -> STret s a
 liftST (ST m) = \s -> case m s of (# s', r #) -> STret s' r
 
-fixST :: (a -> ST s a) -> ST s a
-fixST k = ST $ \ s ->
-    let ans       = liftST (k r) s
-       STret _ r = ans
-    in
-    case ans of STret s' r -> (# s', r #)
-
 {-# NOINLINE unsafeInterleaveST #-}
 unsafeInterleaveST :: ST s a -> ST s a
 unsafeInterleaveST (ST m) = ST ( \ s ->
@@ -67,7 +66,7 @@ unsafeInterleaveST (ST m) = ST ( \ s ->
   )
 
 instance  Show (ST s a)  where
-    showsPrec p f  = showString "<<ST action>>"
+    showsPrec _ _  = showString "<<ST action>>"
     showList      = showList__ (showsPrec 0)
 \end{code}
 
@@ -104,24 +103,18 @@ f = let
 All calls to @f@ will share a {\em single} array!  End SLPJ 95/04.
 
 \begin{code}
-{-# NOINLINE runST #-}
+{-# INLINE runST #-}
+-- 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.
 runST :: (forall s. ST s a) -> a
-runST st = 
-  case st of
-       ST m -> case m realWorld# of
-                       (# _, r #) -> r
-\end{code}
-
-%*********************************************************
-%*                                                     *
-\subsection{Ghastly return types}
-%*                                                     *
-%*********************************************************
-
-The @State@ type is the return type of a _ccall_ with no result.  It
-never actually exists, since it's always deconstructed straight away;
-the desugarer ensures this.
-
-\begin{code}
-data State          s     = S#              (State# s)
+runST st = runSTRep (case st of { ST st_rep -> st_rep })
+
+-- I'm only letting runSTRep be inlined right at the end, in particular *after* full laziness
+-- That's what the "INLINE 100" says.
+--             SLPJ Apr 99
+{-# INLINE 100 runSTRep #-}
+runSTRep :: (forall s. STRep s a) -> a
+runSTRep st_rep = case st_rep realWorld# of
+                       (# _, r #) -> r
 \end{code}