8、正则表达式语言中生成单词及应用

正则表达式语言中生成单词及应用

1. 正则表达式生成二进制数

在正则表达式的应用中，我们可以基于正则表达式生成特定规则的单词。以生成二进制数为例，我们有如下代码：

#lang fsm
;; [natnum>0] →word
;; Purpose: Generate a binary number without leading zeroes,
;; unless its 0, of length <= MAX-LENGTH
(define (generate-bn . n)
  (define MAX-KS-REPS (if (null? n) 10 (first n)))
  ;; regexp →word
  ;; Purpose: Generate a word representing a valid binary number,
  ;; such that the number of Kleene star repetitions is
  ;; in [0..MAX-KS-REPS]
  (define (gen-word r)
    (cond [(singleton-regexp? r) (convert-singleton r)]
          [(concat-regexp? r)
           (let [(w1 (gen-word (concat-regexp-r1 r)))
                 (w2 (gen-word (concat-regexp-r2 r)))]
             (append w1 w2))]
          [(union-reg