[Haskell-beginners] Question about class declaration

24 Jul 2009

      Hi folks,

Once in a while I stumble upon declarations like this:

class EditAction e a | e -> a where
  apply :: a -> e -> a

Why is the vertical bar there? I understand that => defines a context, but
can't find what is the "|" for.

Thanks

Rafael Gustavo da Cunha Pereira Pinto