无法运行＆＃34;计数变化＆＃34; SICP中的代码

Question

我正在阅读SICP，第一章提到的代码如下：

#lang scheme
(define (count-change amount)
  (cc amount 5))

(define (cc amount kind-of-coins)
  (cond ((= amount 0) 1)
        ((or (< amount 0) (= kind-of-coins 0)) 0)
        (else (+ (cc amount
                     (- kind-of-coins 1))
                 (cc (- amount
                        (first-denomination kind-of-coins))
                     kind-of-coins)))))

(define (first-denomination kinds-of-icons)
  (cond ((= kinds-of-icons) 1)
        ((= kinds-of-icons) 5)
        ((= kinds-of-icons) 10)
        ((= kinds-of-icons) 25)
        ((= kinds-of-icons) 50)))

(count-change 100)

我将代码输入DrRacket，但我无法成功运行，我已经尝试了一小时，不知道什么是错的。

Answer 1

您遇到first-denominations问题，=需要两个操作数导致arity错误。所以，它应该看起来像

(define (first-denomination kinds-of-icons)
  (cond ((= kinds-of-icons 1) 1)
        ...)