[project @ 1999-07-27 11:12:05 by simonmar]

add unofficial/undocumented function:

    mkWeakIORef :: IORef a -> IO () -> IO (Weak (IORef a))

for weak pointers to IORefs.  This avoids some of the problems with
inlining disturbing the semantics of mkWeak by making the weak key
point to the primitive MutVar instead of the box.

ghc/lib/exts/IOExts.lhs

@@ -23,6 +23,8 @@ module IOExts
         , readIORef
         , writeIORef
 
+	, mkWeakIORef
+
 	, IOArray	-- instance of: Eq
 	, newIOArray
 	, boundsIOArray
@@ -71,6 +73,7 @@ import PrelHandle ( openFileEx, IOModeEx(..),
 		  )
 import PrelST
 import PrelArr
+import PrelWeak
 import PrelGHC
 import PrelHandle
 import PrelErr
@@ -109,6 +112,10 @@ newIORef v = stToIO (newVar v) >>= \ var -> return (IORef var)
 readIORef  (IORef var) = stToIO (readVar var)
 writeIORef (IORef var) v = stToIO (writeVar var v)
 #endif
+
+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 #)
 \end{code}
 
 \begin{code}