(let stack (fun () {
  (mut data [])

  (let push (fun (value) (set data (concat [value] data))))
  (let popTop (fun () {
    (let res (head data))
    (pop! data 0)
    res }))
  (let isEmpty? (fun () (empty? data)))

  (fun (&data &push &popTop &isEmpty?) ()) }))

(let myStack (stack))
(myStack.push 1)
(myStack.push 2)
(myStack.push 3)

(print myStack.data)

(print "top: " (myStack.popTop))
(print myStack.data)

(print "empty: " (myStack.isEmpty?))
(myStack.popTop)
(myStack.popTop)
(print "empty: " (myStack.isEmpty?))