stack.hs

module Stack(Stack, empty, empty', pop, push, push', s) where

newtype Stack a = Stack [a] deriving Show

empty :: Stack a
empty = Stack []

empty' :: Stack a -> ((), Stack a)
empty' _ = ((), Stack [])

pop :: Stack a -> (a, Stack a)
pop (Stack (x:xs)) = (x, Stack xs)

push :: a -> Stack a -> Stack a
push x (Stack xs) = Stack (x:xs)

push' :: a -> Stack a -> ((), Stack a)
push' x (Stack xs) = ((), Stack (x:xs))

s = push 5 $ push 4 $ push 3 $ push 2 $ push 1 $ empty