[project @ 2005-03-15 12:15:15 by malcolm]

[ghc-base.git] / Control / Concurrent / MVar.hs

diff --git a/Control/Concurrent/MVar.hs b/Control/Concurrent/MVar.hs
index bf9fc5c..ea037ba 100644 (file)
--- a/Control/Concurrent/MVar.hs
+++ b/Control/Concurrent/MVar.hs
@@ -36,9 +36,7 @@ module Control.Concurrent.MVar
 #ifdef __HUGS__
 import Hugs.ConcBase ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
                  tryTakeMVar, tryPutMVar, isEmptyMVar,
-                  readMVar, swapMVar,
                )
-import Hugs.Exception ( throwIO )
 #endif
 
 #ifdef __GLASGOW_HASKELL__
@@ -50,13 +48,6 @@ import GHC.Conc      ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
 import Prelude
 import Control.Exception as Exception
 
-#ifdef __HUGS__
--- This is as close as Hugs gets to providing throw
-throw :: Exception -> IO a
-throw = throwIO
-#endif
-
-#ifdef __GLASGOW_HASKELL__
 {-|
   This is a combination of 'takeMVar' and 'putMVar'; ie. it takes the value
   from the 'MVar', puts it back, and also returns it.
@@ -70,8 +61,11 @@ readMVar m =
 
 -- |Swap the contents of an 'MVar' for a new value.
 swapMVar :: MVar a -> a -> IO a
-swapMVar mvar new = modifyMVar mvar (\old -> return (new,old))
-#endif
+swapMVar mvar new =
+  block $ do
+    old <- takeMVar mvar
+    putMVar mvar new
+    return old
 
 {-|
   'withMVar' is a safe wrapper for operating on the contents of an