On Jan 10, 2008 1:36 PM, Bulat Ziganshin <[EMAIL PROTECTED]> wrote: > 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
I'm not sure that's a good argument. It doesn't need a Num dictionary, it only needs an A dictionary. That's what it says. You only need a Num dictionary in order to construct an A dictionary, which seems perfectly reasonable. Luke _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
