The situation with Enum on Ratio is pretty bad but at least it's not hopeless, since rational numbers are at least exact. But for Float/Double it seems to be a total disaster area. Since it seems to be impossible to abolish Enum Float/Double altogether, would it at least be possible to make it rather more useful, by making succ x return the next representable float after x (or x if x is non-finite) and pred x the previous representable float. This would (a) be useful; (b) make mathematical sense; (c) is tricky to implement with the existing primitives.
Before someone else points it out, this is of course unimplementable should someone in the future implement infinite-precision reals in Haskell, but as (barring a solution to the halting problem) Eq would be as well, that does not bother me. My preference would be for succ (+-0) to return the smallest positive real, since then you could define succ x to be the unique y with x < y and forall z . z < y => not (x < z), where such a y exists, and I'm not sure if the Haskell standard knows about signed zeros. Feri wrote > Everybody working with floats should know their quirks While in an ideal world, everyone who represented a mouse position or anything else as a float should have a PhD in numerical analysis, in practice they do not. Indeed I think the Haskell Library Report contains quite a few examples of floating point code which a numerical analyst would have written rather better. So I don't think it's good enough to treat every Float/Double operation as if it had an implicit "UNSAFE" flag indicating that the compiler was entitled to wierd behaviour only comprehensible to experts, as seems to be the case with floating enumerations now. _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
