| I'm seeing a bit of this now, and the error messages GHC spits out | are hilarious! e.g. | | My brain just exploded. | I can't handle pattern bindings for | existentially-quantified constructors. | | and | | Couldn't match `Bool' against `Bool' | Expected type: Bool | Inferred type: Bool | The first of these is defensible, I think. It's not at all clear (to me anyway) what pattern bindings for existentially-quantified constructors should mean. The second is plain bogus. GHC should never give a message like that. Which version of the compiler are you using? If you can send a small example I'll try it on the latest compiler. Simon