On Wednesday 04 Jan 2006 3:25 pm, Christian Maeder wrote:
I would not like to drop biasing distinction, as I don't think this costs too much. With biasing, maps could be implemented via "biased sets" (Set (MapEntry a b)):
data MapEntry a b = a := b
instance Eq/Ord a => Eq/Ord (MapEntry a b) where compare (a1 := _) (a2 := _) = compare a1 a2
Yikes! You've just done exactly the Bad Thing I was talking about :-). This is broken IMO. E.G. val :: MapEntry a b -> b We can now have (val x) and (val y) yielding different results even though x and y may be "equal", according to the above Ord instance. But I guess you know all this already, so I'm somewhat surprised by this suggestion. I think we should be clear about why we define classes (and instances thereof) at all. Is it because they provide some kind of semantic guarantee, or because they save lazy programmers the effort of passing arbitrary functions about as explicit arguments? I hope it's the former :-) Regards -- Adrian Hey