mainbak01_01.hs

module Mainbak01_01 where
import Stack

{-
comb :: Num a =>
        (Stack a -> (a, Stack a)) 
     -> (Stack a -> (a, Stack a))
     ->  Stack a -> (a, Stack a)
comb m n = \stack0 ->
           let (x1, stack1) = m stack0
               (x2, stack2) = n stack1
           in  (x1+x2, stack2)
-}

comb :: (Stack a -> (a, Stack a)) 
     -> (Stack a -> (a, Stack a))
     -> (a -> a -> a)
     ->  Stack a -> (a, Stack a)
comb m n f = \stack0 ->
           let (x1, stack1) = m stack0
               (x2, stack2) = n stack1
           in  (f x1 x2, stack2)

main = do
{-
  print $ pop `comb` pop $ s 
  print $ pop `comb` pop `comb` pop $ s
-}
  print $ (pop `comb` pop) (+) $ s
  print $ ((pop `comb` pop) (+) `comb` pop) (*) $ s