Remove Control.Parallel*, now in package parallel

[haskell-directory.git] / Data / IORef.hs

diff --git a/Data/IORef.hs b/Data/IORef.hs
index af8ebda..7a6ec7d 100644 (file)
--- a/Data/IORef.hs
+++ b/Data/IORef.hs
@@ -27,7 +27,7 @@ module Data.IORef
 #endif
        ) where
 
-import Prelude
+import Prelude -- Explicit dependency helps 'make depend' do the right thing
 
 #ifdef __HUGS__
 import Hugs.IORef
@@ -48,13 +48,10 @@ import NHC.IOExtras
     , newIORef
     , readIORef
     , writeIORef
+    , excludeFinalisers
     )
 #endif
 
-#ifndef __NHC__
-import Data.Dynamic
-#endif
-
 #if defined(__GLASGOW_HASKELL__) && !defined(__PARALLEL_HASKELL__)
 -- |Make a 'Weak' pointer to an 'IORef'
 mkWeakIORef :: IORef a -> IO () -> IO (Weak (IORef a))
@@ -75,7 +72,7 @@ modifyIORef ref f = writeIORef ref . f =<< readIORef ref
 --
 -- Extending the atomicity to multiple 'IORef's is problematic, so it
 -- is recommended that if you need to do anything more complicated
--- then using 'MVar' instead is a good idea.
+-- then using 'Control.Concurrent.MVar.MVar' instead is a good idea.
 --
 atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b
 #if defined(__GLASGOW_HASKELL__)
@@ -86,4 +83,11 @@ 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
+#elif defined(__NHC__)
+atomicModifyIORef r f =
+  excludeFinalisers $ do
+    a <- readIORef r
+    let (a',b) = f a
+    writeIORef r a'
+    return b
 #endif