Project Euler Problem 026

import Data.List
import Data.Ord
nums :: [Integer]
nums = [ n | n <- [3,5..], n `mod` 5 /= 0 ] --偶数と5の倍数を省いてる
period :: Integer -> Integer
period n = head $ [ p | p <- [1..], (10^p - 1) `mod` n == 0 ]
ans1 :: Integer
ans1 = fst $ maximumBy (comparing snd) $ map(\x->(x,period x)) $ takeWhile (<1000) nums
-- 983
main :: IO ()
main = print ans1