Hello Mark, Thursday, January 10, 2008, 4:25:20 PM, you wrote: "instance Num a =>> A a"
Mean the same thing as
"instance A (forall a.Num a=>a)"
programmers going from OOP world always forget that classes in Haskell doesn't the same as classes in C++. *implementation* of this instance require to pass dictionary of Num class along with type. now imagine the following code: f :: A a => a -> a f cannot use your instance because it doesn't receive Num dictionary of type `a`. it is unlike OOP situation where every object carries the generic VMT which includes methods for every class/interface that object supports as usual, i suggest you to study http://haskell.org/haskellwiki/OOP_vs_type_classes first and especially two papers mentioned in References there -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com