hailstone :: Integer -> Integer
hailstone n
  | n `mod` 2 == 0 = n `div` 2
  | otherwise      = 3*n + 1
hailstone :: Integer -> Integer
hailstone n
  | n `mod` 2 == 0 = n `div` 2
  | otherwise      = 3*n + 1
hailstone n
  | n `mod` 2 == 0 = n `div` 2
  | otherwise      = 3*n + 1