, newIORef
, readIORef
, writeIORef
+ , updateIORef
, mkWeakIORef
\end{code}
\begin{code}
-newIORef :: a -> IO (IORef a)
-readIORef :: IORef a -> IO a
-writeIORef :: IORef a -> a -> IO ()
+newIORef :: a -> IO (IORef a)
+readIORef :: IORef a -> IO a
+writeIORef :: IORef a -> a -> IO ()
#ifdef __HUGS__
type IORef a = STRef RealWorld a
writeIORef (IORef var) v = stToIO (writeVar var v)
#endif
+updateIORef :: IORef a -> (a -> a) -> IO ()
+updateIORef ref f = do
+ x <- readIORef ref
+ let x' = f x
+ writeIORef ref x'
+ -- or should we return new value ? (or old?)
+
mkWeakIORef :: IORef a -> IO () -> IO (Weak (IORef a))
mkWeakIORef r@(IORef (MutableVar r#)) f = IO $ \s ->
case mkWeak# r# r f s of (# s1, w #) -> (# s1, Weak w #)