Donald Bruce Stewart wrote:
should Rational, or something similar be used instead, given that Doubles and Float are broken for a lot of basic things (like Eq and Ord), much as we default to Integer already.
The issues raised regarding Rational was that you can unexpectedly build up large precision, and performance in general, of course.
Well, non-broken Eq and Ord very much depend on large precision. In a sense, the instances of Eq and Ord for floating point numbers are wrong. What about rolling new classes for approximate equality and ordering? class ApproxEq a where (≈) :: a -> a -> Bool -- almost equal to class ApproxOrd a where << :: a -> a -> Bool -- really less than >> :: a -> a -> Bool -- really greater than together with phantom-epsilon data Eps10 newtype Floating e = F Double instance ApproxEq (Floating Eps10) where x ≈ y = abs (x-y) < 1e-10 Regards, apfelmus