[project @ 2001-04-11 10:41:46 by sewardj]

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

diff --git a/ghc/lib/std/PrelConc.lhs b/ghc/lib/std/PrelConc.lhs
index 0122dd8..32240b4 100644 (file)
--- a/ghc/lib/std/PrelConc.lhs
+++ b/ghc/lib/std/PrelConc.lhs
@@ -1,5 +1,5 @@
 % -----------------------------------------------------------------------------
-% $Id: PrelConc.lhs,v 1.22 2001/02/13 15:23:33 rrt Exp $
+% $Id: PrelConc.lhs,v 1.23 2001/02/15 10:02:43 simonmar Exp $
 %
 % (c) The University of Glasgow, 1994-2000
 %
@@ -34,13 +34,14 @@ module PrelConc
        , takeMVar      -- :: MVar a -> IO a
        , putMVar       -- :: MVar a -> a -> IO ()
        , tryTakeMVar   -- :: MVar a -> IO (Maybe a)
+       , tryPutMVar    -- :: MVar a -> a -> IO Bool
        , isEmptyMVar   -- :: MVar a -> IO Bool
 
     ) where
 
 import PrelBase
 import PrelMaybe
-import PrelErr ( parError, seqError )
+import PrelErr         ( parError, seqError )
 import PrelIOBase      ( IO(..), MVar(..) )
 import PrelBase                ( Int(..) )
 import PrelException    ( Exception(..), AsyncException(..) )
@@ -128,6 +129,12 @@ putMVar (MVar mvar#) x = IO $ \ s# ->
     case putMVar# mvar# x s# of
         s2# -> (# s2#, () #)
 
+tryPutMVar  :: MVar a -> a -> IO Bool
+tryPutMVar (MVar mvar#) x = IO $ \ s# ->
+    case tryPutMVar# mvar# x s# of
+        (# s, 0# #) -> (# s, False #)
+        (# s, _  #) -> (# s, True #)
+
 newMVar :: a -> IO (MVar a)
 newMVar value =
     newEmptyMVar       >>= \ mvar ->