Hi,

No, it doesn't work yet. So I turn the question around: Will GADT's and other extensions be supported by Hoogle in the future?

To some degree, yes. A GADT will probably be recorded as though it was a normal ADT for type matching purposes. It's similar with forall at the moment, they are entirely dropped for type matching purposes, but are searched.

Without such support, how useful would it be to include Hoogle support in haddock-ghc?

I would have thought quite useful, for example if you are going to hoogle something like Yampa, you'll need something which can at least ignore the GADT's. My larger concern was if haddock-ghc is going to replace haddock one day, then I'll definately want --hoogle in there. Thanks Neil