OOT

class Stack
    export push, pop, isEmpty, top

    var items : array 1..100 of int
    var size : int := 0

    procedure push (item : int)
        size := size + 1
        items(size) := item
    end push

    function pop : int
        const val := items(size)
        size := size - 1
        result val
    end pop

    function top : int
        result items(size)
    end top

    function isEmpty : boolean
        result size = 0
    end isEmpty
end Stack

var s : ^Stack
new Stack, s

s -> push(10)
s -> push(20)
s -> push(30)

put "Top: ", s -> top
put "Pop: ", s -> pop
put "Pop: ", s -> pop
put "Empty? ", s -> isEmpty
put "Pop: ", s -> pop
put "Empty? ", s -> isEmpty