http://urasunday.com/u-2_09/comic/002_001.html 全然計算終わんねえワロタ

ackerman.hs

f :: Integer -> Integer
f n = n + 1

b :: Integer -> Integer -> Integer
b m n
  | m == 0 && n >  0 = f n
  | m >  0 && n == 0 = b (m - 1) 1
  | otherwise        = b (m - 1) (b m (n - 1))

g :: Integer -> Integer
g x = b x x

main :: IO ()
main = do
  x <- getLine
  y <- getLine
  let answer = b (read x) (read y)
  print $ show answer