I was wondering whether there might be any sort of trick one could use to create an empty "Weak a", i.e. one that has already been GCed? It should be possible to create such a pointer without having an object of type a. mkEmptyWeakPtr :: IO (Weak a) I know I could get this effect by using instead a "Maybe (Weak a)", but that's ugly and adds an additional layer of redirection. The point is that the weak pointer is being used to cache a value, but I'd like to not fill the cache until I actually need to read it. i.e. I have a data type AntiMemo (IO a) (IORef (Weak a)) where the second term is a cache of the result of the first, which is really a pure function, but I'm using the IO monad to force reevaluation, so the result, which is large, can be discarded and recomputed. So I could change this to AntiMemo (IO a) (IORef (Maybe (Weak a))) but it just seems a shame when Weak already effectively has a "Nothing" value type. I suppose one could also make it a "Weak (Maybe a)", but in any case, I'd rather be able to just initialize the IORef to an empty weak pointer, so there wouldn't need to be any extra code when reading the value. -- David Roundy http://www.abridgegame.org