Am Donnerstag, 24. April 2008 21:27 schrieb John Meacham:
On Thu, Apr 24, 2008 at 08:48:15PM +0200, Wolfgang Jeltsch wrote: […]
I also have some remark: Why not write
class Eq a => Num a = (Additive a, Multiplicative a)
instead of
class Num a = Eq a => (Additive a, Multiplicative a)
Well, because you can think of 'Num a' as an alias for 'Eq a => (Additive a, Multiplicative a)', not that Eq is a superclass of Num which the class declaration syntax implies.
Hmm, in what way is Num a an alias for Eq a => (Additive a, Multiplicative a)? You cannot write this:
square :: (Eq a => (Additive a, Multiplicative a)) => a -> a
I would say: “Under the condition that Eq a holds, Num a is an alias for (Additive a, Multiplicative a). And this seems to be perfectly expressed by my above proposal. Best wishes, Wolfgang