plp/haskell/haskell7.hs

import Control.Monad.State
type Stack = [Int]


--Define the pop function
pop :: Stack -> (Int, Stack)
pop (x:xs) = (x, xs)

--Define the push function
push :: Int -> Stack -> ((), Stack)
push x xs = ((), x:xs)

stackManip :: Stack -> (Int, Stack)
stackManip stack = let
    (a, stack1) = pop stack
    (b, stack2) = pop stack1
    ((), stack3) = push 100 stack2
    (c, stack4) = pop stack3
    in pop stack4

popM :: State Stack Int
popM = do
    x:xs <- get
    put xs
    return x

pushM :: Int -> State Stack ()
pushM a = do
    xs <- get
    put (a:xs)
    return()

stackManipM :: State Stack Int
stackManipM = do
    popM
    popM
    pushM 100
    popM
    popM

stackStuff :: State Stack ()
stackStuff = do
    a <- popM
    if (a==5)
        then return ()
        else do
            pushM 3
            pushM 8
            get