IStack main() {
  IStack x = new CountedListStack : IStack();
  IStack y = null;

  x.push(new CharBox : Character(value = '5'));
  x.push(new IntBox  : Integer(value = 3));

  y = x.copy();

  while(!y.empty()) {
    Any curr = y.pop();

    if curr isa Character {
      printLine("Got a character");
    } else {
      if curr isa Integer {
        printLine("Got an integer");
      } else {
        printLine("Got something else");
      };
    };
  };

  x;
}