Sebastian Sylvan:
primes :: [Integer] primes = 2 : filter (null . primeFactors) [3,5..]
primeFactors :: Integer-> [Integer] primeFactors n = factor n primes where factor m (p:ps) | p*p > m = [] | m `mod` p == 0 = p : factor (m `div` p) (p:ps) | otherwise = factor m ps
Your definition gives a strange meaning to primeFactors. I'd want that for all n, product (primeFactors n) == n. I think this law holds for the code posted by Olivier. Of course I'd beautify his definition slightly by writing primes = 2 : filter isPrime [3,5..] isPrime = null . drop 1 . primeFactors primeFactors n | n >= 2 = factor primes n factor pr@(p:ps) n | p*p > n = [n] | r == 0 = p : factor pr q | otherwise = factor ps n where (q,r) = quotRem n p Kalman ---------------------------------------------------------------------- Get a free email account with anti spam protection. http://www.bluebottle.com/tag/2