Is there any particular reason there isn't a class for monads for which things like IORef/STRef exist? I suppose the naive approach would require functional dependencies + mp typeclasses[1], which is a decent reason :), but has anyone come up with something that doesn't require extensions? [1] i'm thinking of something like: class MonadRef m r | m -> r, r -> m where newRef :: a -> m (r a) readRef :: r a -> m a writeRef :: r a -> a -> m () updateRef :: (a -> a) -> r a -> m () i think you need the FD in both directions (certainly you need m -> r); i think the latter would serve to disambiguate things like readRef (having not actually implemented this, though, i don't know). - Hal -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume