[Hugs-bugs] FDs and extistentials

[Ross Paterson]

On Mon, Jan 30, 2006 at 05:21:50PM +0300, Bulat Ziganshin wrote:
> the attached program compiles under GHC, but not with Hugs. as far as
> i see, Hugs don't use dependencies in class headers to figure out that
> there is only one "vMkIOError" that can be called in the last
> definition

The example (slightly simplified):

	class (Monad m) => Stream m h | h->m where
		vMkIOError :: h -> Int

	data BinHandle = forall h . Stream IO h => BinH h

	instance Stream IO BinHandle where
		vMkIOError (BinH h) = vMkIOError h

OK, I think it's a bug (though the example is bizarre).

Sadly Hugs's support for FDs is rough around the edges (and unlikely
to improve soon).