4 Oct
2001
4 Oct
'01
8:50 a.m.
On Wed, Oct 03, 2001 at 11:52:30AM -0400, Jan-Willem Maessen wrote:
Earlier, Simon says:
Indeed, if none of the classes have a method that returns an a-value without also consuming one (urk-- strictly, I think, sigh) then the same holds.
Strictness alas matters. Here's the witness:
class Num a => ZeroList a where consZero :: a -> [a] consZero _ = 0:xs
Err, "Num a" is already a bad context by Simon's criterion because of "fromInteger", which is what ultimately causes the problem in this case. I don't see how strictness can be relevant, since it is a property of a class instance, not a class. Best, Dylan