> That's completely different. The class in that case guarantees that > the type has an "Eq" class, so it's okay to use the functions in the > "Eq" class. You're using the guarantees supplied by the class. When > you write instances, it's the other way around, the class has > *requirements* that you must fulfill -- and there are multiple ways of > doing it (Haskell won't guess, it will obey what you tell it -- if you > don't give any class constraints it won't assume that they are there).
Hi Sebastian, could you please point me to a reference (paper/note/something else) that explains that class constraint in a class definition is a guarantee with regard to a type declaration but a requirement with regard to an instance declaration? David Tolpin _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
