Prime Test

-- Type problem

-- simple prime test
prime :: Integral a => a -> Bool
prime 1 = True
prime n
  | n < 1 = False
  | otherwise = ptestn m0
  where
    m0 = n `div` 2
    ptestn :: Integral a => a -> Bool
    ptestn 1 = True
    ptestn m = n `mod` m > 0 && ptestn (m - 1)

-- foo
foo :: Integral a => a -> Bool
foo n = n == sqr n
  where
    sqr :: Integral b => b -> b
    sqr 1 = 1
    sqr m = m*m