On Wednesday 24 October 2001 05:13 am, John Hughes wrote:
The program below produces this error message (with -98 in the February 2001 version):
ERROR Bug.hs:5 - Instance of Num Int required for definition of f
Pardon?
data T class C a b | b->a where m :: a -> (Bool, b) instance C Int T instance C a b => C [a] [b] f () = located :: [T] where (_,located) = m [0]
Using generic instances with functional dependencies isn't fully supported in Hugs. Many people have reported bugs that are a result of this. Fixing it, however, looks to involve a significant overhaul of context simplification, an exercise I've managed to put off doing for quite some time ;-) But for this particular bug, I have a patch that may get you some mileage. It will be in the upcoming release. --Jeff