class STACK{T} is
  private attr stack :LLIST{T};

  create:SAME is
    res ::= new;
    res.stack := #LLIST{T};
    return res;
  end;

  push(elt: T) is
    stack.insert_front(elt);
  end;

  pop: T is
    if ~stack.is_empty then
      stack.rewind;
      r ::= stack.current;
      stack.delete;
      return r;
    else
      raise "stack empty!\n";
    end;
  end;

  top: T is
    stack.rewind;
    return stack.current;
  end;

  is_empty: BOOL is
    return stack.is_empty;
  end;
end;