Flolac week of code 3: goldbach

goldbach.hs

goldbach :: Int -> Maybe(Int, Int)
goldbach n = search halfOfPrimes where
  search [] = Nothing
  search (x:xs) = if isPrime (n - x) then Just (x,  n - x) else search xs
  halfOfPrimes = 2 : [ x | x <- [3, 5..half], isPrime x]
  half = div n 2

isPrime :: Int -> Bool
isPrime 2 = True
isPrime n = not $ any isFactor (2 : [3, 5 .. (square n)])
  where square = floor . sqrt . fromIntegral
        isFactor x = mod n x == 0