SICP 問題 4.49

自然言語の構文解析用プログラムを少し改造するだけで文章の生成ができる．

(define (an-element-of items)
  (require (not (null? items)))
  (amb (car items) (amb (cdr items))))

(define (parse-word word-list)
  (list (car word-list)
        (an-element-of (cdr word-list))))

(define (generate-sentence)
  (parse-sentence))