mainbak00.hs

module Mainbak00 where
import Stack

-- スタックから 2 つの要素を取り出して足し合わせる
sumTwoElem :: Num a => Stack a -> (a, Stack a)
sumTwoElem stack0 = let (x1, stack1) = pop stack0
                        (x2, stack2) = pop stack1
                    in  (x1+x2, stack2)

-- スタックから 4 つの要素を取り出して足し合わせる
sumFourElem :: Num a => Stack a -> (a, Stack a)
sumFourElem stack0 = let (x1, stack1) = pop stack0
                         (x2, stack2) = pop stack1
                         (x3, stack3) = pop stack2
                         (x4, stack4) = pop stack3
                     in  (x1+x2+x3+x4, stack4)
 
sumFourElem' :: Num a => (Stack a -> (a, Stack a))
             -> Stack a 
             -> (a, Stack a)

sumFourElem' f  = \stack0 ->
                  let (x1, stack1) = f stack0
                      (x2, stack2) = f stack1
                      (x3, stack3) = f stack2
                      (x4, stack4) = f stack3
                  in  (x1+x2+x3+x4, stack4)

main = do print s
          print $ sumTwoElem s
          print $ sumFourElem s 
          print $ sumFourElem' pop $ s