On Mon, 2009-01-19 at 12:10 -0800, Iavor Diatchki wrote:
I usually avoid using the "newtype" trick as I find it inconvenient: usually the newtype does not have the same operations as the underlying type and so it cannot be used directly, and if you are going to wrap thing just when you use the class methods,
OTOH, I think you mean here `when you use class methods and when you use overloaded functions'.
Sure, the point is that you are essentially adding a type annotation, which is like using a non-overloaded function. Compare, for example: "mappend add x y" and "getSum (mappend (Sum x) (Sum y))". I think that the first one is quite a bit more readable but, of course, this is somewhat subjective.
Right. Of course, this issue comes up quite frequently; even sort :: Ord alpha => [alpha] -> [alpha] Needs to be specialized to non-standard Ord instances. I think that, if we're going to restrict type classes to only those cases where we never want to specialize an overloaded function to a non-standard instance, that we're going to end up with Eq, Num, and maybe Functor as classes. I'm not sure a general language mechanism is really needed just for those three. jcc