エラトステネスのふるい

gistfile1.hs

primenumber :: Int -> [Int]
primenumber x
    | 1 > x = error "argument 0 must be >0."
    | 1 == x = []
primenumber x = sieve [2..x]
    where
    s = (sqrt . fromIntegral) x
    sieve :: [Int] -> [Int]
    sieve (x:[]) = x : []
    sieve all@(x:xs)
            | s < fromIntegral x = all
            | otherwise = x : sieve [ x' | x' <- xs, 0 /= mod x' x ]