So, it is a language extension as I predicted. A cool one, by the way.
Thank you all!
On Fri, Jul 24, 2009 at 09:44, Brent Yorgey
On Fri, Jul 24, 2009 at 09:41:34AM -0300, Rafael Gustavo da Cunha Pereira Pinto wrote:
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.
It's a functional dependency: the e -> a means that the type e determines the type a, that is, there can only be one instance of EditAction for any particular type e.
-Brent _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners
-- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.