はすけるで素数判定

Prime.hs

module Prime(
    prime
) where

prime :: Int -> Bool
prime x | x < 0        = error "the argument should be larger than zero."
        | x == 1       = False
        | x == 2       = True
        | mod x 2 == 0 = False
        | otherwise    = all (\y -> mod x y /= 0 || x == y) (take (x - 3) [3, 5..])

PrimeTest.hs

import Test.HUnit
import Prime

tests = test [prime  1 ~?= False,
              prime  2 ~?= True,
              prime  3 ~?= True,
              prime  4 ~?= False,
              prime  5 ~?= True,
              prime  6 ~?= False,
              prime  7 ~?= True,
              prime  8 ~?= False,
              prime  9 ~?= False,
              prime 10 ~?= False,
              prime 11 ~?= True,
              prime 12 ~?= False,
              prime 13 ~?= True,
              prime 14 ~?= False,
              prime 15 ~?= False,
              prime 16 ~?= False,
              prime 17 ~?= True,
              prime 18 ~?= False,
              prime 19 ~?= True,
              prime 20 ~?= False]

main = do
       runTestTT tests