/* File: chom1.pl
   Author: Mihaela Malita
   Title: A grammar to build sentences in English   
          Plural/Singular
    Our vocabulary consists of:
    3 nouns:    boy , girl , dog 
    and     3 verbs:    likes , hates , loves
    
    Plural(pl) versus Singular (sg) 
    the boy like the dog        incorrect
    the boy likes the dog       correct

    We have to put the condition that 
    the number of the noun has to be the same as the number of the verb.

        ?-phrase(sentence(N),[the,boy,likes,the,dog]). 
        N = sg 
        ?- phrase(sentence(pl),X).
        [the,boys,like,the,dogs]
        ..
        ?- phrase(sentence(I),[the,boys,likes,the,dog]).
        no
        ?- phrase(sentence(N),[the,boy,likes,the,dogs]).
        N = sg 
        Yes
*/

sentence(Nr) -->    noun_ph(Nr),verb_ph(Nr).
noun_ph(Nr) -->     det(Nr),noun(Nr).
verb_ph(Nr) -->     verb(Nr),noun_ph(_).

det(_) -->  [the].  % determiner

noun(sg) --> [boy]; [dog]; [girl].
noun(pl) -->   [boys]; [dogs]; [girls].

verb(sg) --> [likes] ; [hates] ; [loves].
verb(pl) --> [like]; [hate]; [love].