[Haskell-cafe] Current research on overlapping/closed type families?

What's the status of overlapping/closed type families? I'm interested in something like the following, which can currently be implemented in GHC with Oleg-magic using functional dependencies, but cannot, to my knowledge, be implemented with type families: data HTrue = HTrue data HFalse = HFalse type family IsFunction f {- not legal in GHC6.10 -} type instances IsFunction (a -> b) = HTrue IsFunction a = HFalse -- ryan