关于在 str 中查找元音的 Scheme racket 问题

Question

我试图编写有关 get-vowels 及其运行 100% 的代码，但我试图显示这 4 个输出，我也只想显示这 4 个输出，但找不到解决方案。

> (define vowels (string->list "aeiouyæøå"))
> (define (vowel? c)
  (member c vowels))
> (define (filter p xs)
  (define (more) (filter p (cdr xs)))
  (cond
    ((null? xs)    '())
    ((p (car xs))  (cons (car xs) (more)))
    (else          (more))))
> (define (count-vowels s)
  (length (filter vowel? (string->list s))))
> (display (count-vowels "foobarbaz"))
4

示例：输出： 4个 “ooaa”

Answer 1

您不应该将过程命名为 filter，它与 完全按照您的意愿 做事的内置过程相冲突。事实上，你只需要删除你的 filter 实现，它就会起作用:)

(define vowels (string->list "aeiouyæøå"))

(define (vowel? c)
  (member c vowels))

(define (count-vowels s)
  (length (filter vowel? (string->list s))))

; there's a bit of code duplication here, you could
; refactor it if you want, to avoid repeating yourself    
(define (extract-vowels s)
  (list->string (filter vowel? (string->list s))))

(count-vowels "foobarbaz")
=> 4

(extract-vowels "foobarbaz")
=> "ooaa"

关于在 str 中查找元音的 Scheme racket 问题

Scheme racket question about finding vowels in str

racket