Scheme上的SHOW/READ/READ-LINE/etc程序

Question

我正在学习Scheme并使用一些例子来看看这些东西在起作用.

我正在使用Eclipse的Chicken解释器.

尝试运行以下代码时:

(define (bottles n)
  (if (= n 0)
      'burp
      (begin (verse n)
         (bottles (- n 1)))))

(define (verse n)
  (show (cons n '(bottles of beer on the wall)))
  (show (cons n '(bottles of beer)))
  (show '(if one of those bottles should happen to fall))
  (show (cons (- n 1) '(bottles of beer on the wall)))
  (show '()))

(bottles 3)

我收到以下错误:

#;1> #;2>  Note: the following toplevel variables are referenced but unbound:

  verse (in bottles)
#;3> #;3>  Note: the following toplevel variables are referenced but unbound:

  show (in verse)   show (in verse)   show (in verse)   show (in verse)   show (in verse)

Error: unbound variable: show

Call history:

<syntax>      (bottles 3)   <eval>    (bottles 3)   <eval>    [bottles] (= n 0)     <eval>    [bottles] (verse n)   <eval>    [verse] (show (cons n (quote (bottles of beer on the wall)))) <--

有人知道为什么吗？当然,如果我创建一个说"show"会显示东西的程序,那么它可以工作,但是应该显示一个来自Scheme的标准程序吗？因为许多代码通过互联网显示,并且没有"显示"程序描述.同样的事情发生在READ/READ-LINE等.

谢谢!

Answer 1

该show过程未定义.作为鸡计划中实施的R5RS的一部分,您可以使用display或write输出,如文档中所示.

但是,功能show很容易实现:

(define (show obj)
  (display obj)
  (newline))