[project @ 2002-10-18 12:28:38 by ross]

Hugs only: simple version of atomicModifyIORef, relying on the absence
of preemption from Hugs.  If Hugs gets Haskell finalizers, they'll have
to be blocked during this operation.

diff --git a/Data/IORef.hs b/Data/IORef.hs
index 55cb52f..527e20a 100644 (file)
--- a/Data/IORef.hs
+++ b/Data/IORef.hs
@@ -20,7 +20,7 @@ module Data.IORef
         readIORef,           -- :: IORef a -> IO a
         writeIORef,          -- :: IORef a -> a -> IO ()
        modifyIORef,          -- :: IORef a -> (a -> a) -> IO ()
-       atomicModifyIORef,    -- :: IORef a -> (a -> (a,b)) -> IO ()
+       atomicModifyIORef,    -- :: IORef a -> (a -> (a,b)) -> IO b
 
 #if !defined(__PARALLEL_HASKELL__) && defined(__GLASGOW_HASKELL__)
        mkWeakIORef,          -- :: IORef a -> IO () -> IO (Weak (IORef a))
@@ -77,7 +77,14 @@ modifyIORef ref f = writeIORef ref . f =<< readIORef ref
 -- then using 'MVar' instead is a good idea.
 --
 atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b
+#if defined(__GLASGOW_HASKELL__)
 atomicModifyIORef (IORef (STRef r#)) f = IO $ \s -> atomicModifyMutVar# r# f s
+#elif defined(__HUGS__)
+atomicModifyIORef = plainModifyIORef   -- Hugs has no preemption
+  where plainModifyIORef r f = do
+               a <- readIORef r
+               case f a of (a',b) -> writeIORef r a' >> return b
+#endif
 
 #ifndef __NHC__
 #include "Dynamic.h"