Simple prime factorization code


primes :: [Integer]
primes = primes' (2:[3,5..])
where primes' (x:xs) = x : primes' (filter (notDivisorOf x) xs)
notDivisorOf d n = n `mod` d /= 0

factors :: [Integer] -> Integer -> [Integer]
factors qs@(p:ps) n
| n <= 1 = []
| m == 0 = p : factors qs d
| otherwise = factors ps n
where (d,m) = n `divMod` p

primeFactors :: Integer -> [Integer]
primeFactors = factors primes