Exercise 4.48: add parsing of adjectives

mceval/amb-natural-language.rkt

@@ -4,6 +4,8 @@
 
 (define articles '(article the a))
 
+(define adjectives '(adjective happy lazy))
+
 ;; output of parse
 '(sentence (noun-phrase (article the) (noun cat))
            (verb eats))
@@ -40,6 +42,7 @@
 
 (define prepositions '(prep for to in by with))
 
+
 (define (parse-prepositional-phrase)
   (list 'prep-phrase
         (parse-word prepositions)
@@ -58,10 +61,11 @@
                              (parse-prepositional-phrase)))))
   (maybe-extend (parse-word verbs)))
 
+;; Extend this to allow an adjective between the article and noun.
 (define (parse-simple-noun-phrase)
   (list 'simple-noun-phrase
         (parse-word articles)
-        (parse-word nouns)))
+        (parse-adjective-phrase)))
 
 (define (parse-noun-phrase)
   (define (maybe-extend noun-phrase)
@@ -71,6 +75,14 @@
                              (parse-prepositional-phrase)))))
   (maybe-extend (parse-simple-noun-phrase)))
 
+;; An adjective phrase is any number of adjectives followed by a
+;; simple noun.
+(define (parse-adjective-phrase)
+  (amb (list (parse-word nouns))
+       (cons
+         (parse-word adjectives)
+         (parse-adjective-phrase))))
+
 
 ;; Exercise 4.45: Output of (parse '(the professor lectures to the student in the class with the cat))