(load "util.scm")
(load "misc/amb.scm")

(define nouns '(noun cat student professor class))
(define verbs '(verb eats studies lectures sleeps))
(define articles '(article the a))
(define prepositions '(prep for to in by with))

(define *unparsed* '())

(define (parse-noun-phrase)
  (list 'noun-phrase
        (parse-word articles)
        (parse-word nouns)))

(define (parse-word word-list)
  (require (not (null? *unparsed*)))
  (require (memq (car *unparsed*) (cdr word-list)))
  (let ((found-word (car *unparsed*)))
    (set! *unparsed* (cdr *unparsed*))
    (list (car word-list) found-word)))

(define (parse input)
  (set! *unparsed* input)
  (let ((sent (parse-sentence)))
    (require (null? *unparsed*))
    sent))

(define (parse-prepositional-phrase)
  (list 'prep-phrase
        (parse-word prepositions)
        (parse-noun-phrase)))

(define (parse-sentence)
  (list 'sentence
         (parse-noun-phrase)
         (parse-verb-phrase)))

(define (parse-verb-phrase)
  (define (maybe-extend verb-phrase)
    (amb verb-phrase
         (maybe-extend (list 'verb-phrase
                             verb-phrase
                             (parse-prepositional-phrase)))))
  (maybe-extend (parse-word verbs)))

(display "\nex-4.45 - parse-sentence\n")

;(sentence (noun-phrase (article the) (noun cat)) (verb eats))

;'(The professor lectures to the student in the class with the cat)


(display "\nex-4.46\n")