G'day all.
I've finally had a chance to implement some of these changes.
Quoting Yitzchak Gale
o I think you are testing w' * w' < n each time, even when you are repeating factors of the same prime p. You only need to do that when you move to the next p.
Actually, it turns out we only test that when we change wheels, which is not very often. There's still some lambda dropping which could be done, but I'm not sure it's worth it.
o You can use divMod (or quotRem) instead of using div and then multiplying. (That's an ancient trick from C. It may not make a difference on modern CPUs.)
Fixed.
o I personally would much prefer a function that only returns prime numbers, not -1, 0, or 1.
I'd like, if I can, to preserve the property that product is a retraction for factor. I've changed it so that factor 1 = [], but I'm unsure what to do with 0 and negative numbers. I think that factor 0 = [0] is the only reasonable thing to return. As for negative numbers, the two easiest solutions are return -1 as a first factor, or negate the first prime factor returned. Even then, you'd have to return factor (-1) = [-1]. Maybe there should be two functions exposed? Cheers, Andrew Bromage