Might it be possible to create a Functor instance for weak pointers? I don't really need to, but it would certainly be handy. Unfortunately, I don't see how it could be implemented, since there's no way to create a new already-tombstoned weak pointer, and without that ability, I can't see how one could do this. I'd like to write weakFmap :: (a -> b) -> Weak a -> Weak b but don't see how I can, since if deRefWeak returns Nothing, I have no way of creating a Weak b that will also return Nothing. :( A simple emptyWeak :: Weak a would be sufficient, as I could then write weakFmap f wa = unsafePerformIO $ do ma <- deRefWeak wa case ma of Nothing -> return emptyWeak Just b -> mkWeakPtr (f b) Nothing -- David Roundy http://www.abridgegame.org