尝试在DrRacket中实现我自己的堆栈对象

(define stack
  (class object%
    (init-field data)
    
    (define/public (push item)
      (set! data (cons item data)))
    
    (define/public (pop)
      (if (empty?)
          (error "Stack is empty")
          (begin
            (define item (car data))
            (set! data (cdr data))
            item)))
    
    (define/public (empty?)
      (null? data))
    
    (define/public (size)
      (length data))
    
    (super-new)))

(define my-stack (new stack (data '())))

(send my-stack push 1)
(send my-stack push 2)
(send my-stack push 3)

(displayln (send my-stack pop)) ; 输出：3
(displayln (send my-stack pop)) ; 输出：2
(displayln (send my-stack pop)) ; 输出：1

(displayln (send my-stack empty?)) ; 输出：#t
(displayln (send my-stack size)) ; 输出：0