stack.hs

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