On Thu, Apr 24, 2008 at 10:21:03PM +0200, Wolfgang Jeltsch wrote:
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.
Hmm... I guess it depends on how you think about it. I tend to think about them in terms of what they are rewritten to rather than a proposition about classes. but perhaps that makes more sense. Will mull on it some.. John -- John Meacham - ⑆repetae.net⑆john⑈