project euler Problem 3

pe3.hs

num = 600851475143
nums = reverse [1..600851475143]

isPrime :: (Integral a) => a -> Bool
isPrime x = (product $ map (mod x) [2..(x-1)]) /= 0

getPrimes :: (Integral a) => [a] -> [a]
getPrimes xs = filter isPrime $ xs

primes = getPrimes nums

isFactor :: (Integral a) => a -> a -> Bool
isFactor x y = (mod x y) == 0

largestPrimeFactor = find (isFactor num) $ primes

thanks! "and" is short-circuit and use sqrt to reduce n to sqrt(n). this works.