Hi > The Eq instance you've given violates the law that (x == y) = True > implies x = y. Of course the Haskell standard doesn't specify this law, > but it should.
Wrong. It shouldn't, it doesn't, and I don't think it even can! > The Haskell standard doen't even specify that compare x y = EQ implies > (x == y) = True, but again it should (what's the purpose of the Eq > constraint on Ord class otherwise). Correct. Yes, this is one law that _should_ be true, along with others: a > b && b > c => a > c a == b => b == a etc. But a == b => a = b is not a law that needs to hold, and not a law that can be stated in Haskell, even as a quickcheck property. Thanks Neil _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
