[Haskell-cafe] Re: Problem with fundeps.

In article , karczma@info.unicaen.fr wrote: GHCi is correct to complain:

class Vspace a v | v -> a

OK, the first parameter ("a") depends on the second ("v").

instance Vspace a a where

And this determines it: the first parameter must always be the same as the second.

instance (Vspace a v) => Vspace a (c->v) where

This is incompatible with the previous instance declaration, since "a" is not the same as "c -> v". And any instance decl that were permitted by the fundep would in any case overlap. -- Ashley Yakeley, Seattle WA