import Data.Array.IO

main::IO()
main = do
     arr <- newArray((0,0),(8,13)) 0 ::IO (IOArray(Int,Int) Int)
     list <- getElems arr
     print list
     push 0 mystack
     return()

data Stack a = Stack [a] deriving Show

empty :: Stack a
empty = Stack []

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

pop :: Stack a -> (Maybe a, Stack a)
pop (Stack []) = (Nothing, Stack [])
pop (Stack (x:xs)) = (Just x, Stack xs)

mystack = empty

Couldn't match type `Stack' with `IO'
    Expected type: IO Integer
      Actual type: Stack Integer
    In the return type of a call of `push'
    In a stmt of a 'do' block: push 0 mystack