On 13 Jul 2007, at 2:58 am, apfelmus wrote:
What I wanted to do is to capture common patterns
x - y >= epsilon abs (x - y) <= epsilon
for comparing floating point numbers in nice functions
x >> y = x - y >= epsilon x ≈ y = abs (x - y) <= epsilon
See Knuth, The Art of Computer Programming, Volume 2, Semi-Numerical algorithms, for a suitable set of predicates and axioms they satisfy. However, they depend on epsilon (or APL's []CT, comparison tolerance). I once implemented the four predicates Knuth discussed in Quintus Prolog (library(fuzzy)). As far as I know, nobody ever used it. I had plans for making the code faster if anybody cared, but no-one did. I suspect these functions would be no more useful in Haskell: anyone who knew enough to use them would know enough not to.