Am Mittwoch, 17. März 2004 13:30 schrieb Ketil Malde:
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Furthermore, having only an equivalence implies that there is a stronger equality below that cannot be also an instance of Eq.
I've already said that I think Eq's (==) should be "structural equality", which I thought meant that there shouldn't be any "deeper" equality.
I think, the name "structural equality" is misleading because it seems to imply that equivalent values have to have the same (internal) structure. If values a and b have different internal representations but are indistinguishable for the library user, than a == b should hold. But I totally agree with you that == should mean equality and not anything different. And this is also what The Haskell Report says in § 6.3.1: "The Eq class provides equality (==) and inequality (/=) methods." So a lot of the MultiSet/Bag and the bias discussion can be avoided. DData can and should assume that the Eq methods mean exactly what they are supposed to mean: equality and inequality.
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-kzm
Wolfgang