Question

我正在做一个问题，要求我将字符串中的所有大写字母都转换为小写字母，并将小写字母转换为大写字母，而所有其他字符都保持不变。

下面是我的代码：

(define (switch-case str)
  (list->string
  (cons
  (cond
    [(char-lower-case? (first (string->list str))) (char-upcase (first 
(string->list str)))]
    [(char-upper-case? (first (string->list str))) (char-downcase (first 
(string->list str)))]
    [else (first (string->list str))])
  (switch-case (rest (string->list str))))))

str“ ABC”的错误消息是：字符串->列表：期望给出一个字符串（cons＃\ B（cons＃\ C空））有人可以告诉我我的代码出了什么问题吗？谢谢

Answer 1

递归调用的类型错误。您将[List-of Character]传递给switch-case，但是期望String。

; String -> String
(define (switch-case str)
  (list->string
   (cons
    (swapcase nestr)
    (switch-case
     (rest (string->list str)) ; the type of this expression is [List-of Character]
                 ))))

遵循此模板：

; [List-of Character] -> [List-of Character]
(define (switch-case-charlist cl)
  (cond [(empty? cl) ...]
        [else (... (first cl) ... (switch-case-charlist (rest cl)))]))

; Character -> Character
(define (swap-case-character c)
  ...)

; String -> String
(define (swap-case-string s)
  (list->string (... (string->list s))))

切换字符串的大写和小写

1 个答案: