Question

我需要在方案中生成一个随机的ASCII字母（大写或小写）或字符（但不是数字），我想知道适当的方法是什么。目前我已经获得了代码

(define a 1)
(define b 16)
(define (s8 a b)
  (when (<= a b)
    (if (= (mod a 8) 0)
      (write "h")
      (write a))
    (s8 (+ a 1) b)))
(s8 a b)

有效（没有错误）但是我没有打印随机的ascii字母/字符，而是因为我不知道如何做到这一点。我用Google搜索，但无法找到任何东西。任何帮助，将不胜感激。谢谢！

编辑：

(define random-char
  (let* ((chars '("a" "e" "i" "o" "u"))
         (len (length chars))) 
    (lambda ()
      (list-ref chars (random len)))))
(define a 1)
(define b 16)
(define (s8 a b)
  (when (<= a b)
    (if (= (mod a 8) 0)
      (random-char)
      (write a))
    (s8 (+ a 1) b)))
(s8 a b)

给出错误

1234567
Error: execute: unbound symbol: "random" [s8, s8, s8, s8, s8, s8, s8, s8, random-char]

Answer 1

一种简单的方法是将所有可接受的字符放在一个列表中，然后随机选择一个：

(define random-letter
        ; this is to avoid redefining the list of acceptable letters every time
  (let* ((chars '("a" "e" "i" "o" "u"))
        ; and this is to pre-calculate the length
         (len (length chars))) 
    (lambda () ; the actual procedure, it doesn't require arguments
      (list-ref chars (random len))))) ; pick a random index from list

确保在列表中添加所有需要的字符。使用该程序就像这样简单：

(random-letter)
=> "u"

Answer 2

以下是如何使用工业强度的Scheme派生语言：特别是Racket。它假定了各种功能您可能需要在更简单的Scheme中实现，例如函数制作字符串，在字符和整数之间进行转换，以及PRNG （以及咖喱）。

如果您的方案缺少某些功能，您可能需要编写它，这可能在教育上很有趣，但没有别的。

(define latin-alpha-string
  ;; This assumes that a-z are a sequence of adjacent, increasing
  ;; character codes, as are A-Z, but nothing about their relative values
  (let ([lca (char->integer #\a)]
        (uca (char->integer #\A)))
    ;; build-string makes a string by calling a function which takes an index
    ;; and returns the character at that index.
    (build-string (+ 26 26)
                  (λ (i)
                    (integer->char
                     (if (< i 26)
                         (+ lca i)
                         (+ uca (- i 26))))))))

(define (random-string-char s (rand random))
  ;; The general case: return a random element of a string.  rand, if provided,
  ;; should be a function of one argument, i, which returns a (pseudo-)random
  ;; integer in [0, i).
  (string-ref s (rand (string-length s))))

(define random-latin-alpha-char
  ;; and here's a curried version of the above for latin-alpha strings
  (curry random-string-char latin-alpha-string))

生成随机ASCII字符

2 个答案: