%% A grammar for a VERY small subset of English:

%% sentence -> noun_phrase verb_phrase
%% nounPhrase -> proper_noun
%% nounPhrase -> article adjective noun
%% nounPhrase -> article noun
%% verbPhrase -> intransitive_verb
%% verbPhrase -> transitive_verb noun_phrase
%% article -> list of articles
%% adjective -> list of adjectives 
%% properNoun -> list of proper nouns
%% noun -> list of nouns
%% intransitiveVerb -> list of intransitive verbs
%% transitiveVerb ->  list of transitive verbs

variable(sentence).
variable(nounPhrase).
variable(verbPhrase).
variable(article).
variable(adjective).
variable(properNoun).
variable(noun).
variable(intransitiveVerb).
variable(transitiveVerb).

terminal(X) :- 
    article(X) ;
    adjective(X) ;
    properNoun(X) ;
    noun(X);
    intransitiveVerb(X);
    transitiveVerb(X).

rule(sentence, [nounPhrase, verbPhrase]). 
rule(nounPhrase, [properNoun]).
rule(nounPhrase, [article, adjective, noun]).
rule(nounPhrase, [article, noun]).
rule(nounPhrase, [adjective, noun]).
rule(verbPhrase, [intransitiveVerb]).
rule(verbPhrase, [transitiveVerb, nounPhrase]).
rule(article, [A]) :- article(A).
rule(adjective, [A]) :- adjective(A).
rule(properNoun, [PN]) :- properNoun(PN).
rule(noun, [N]) :- noun(N).
rule(intransitiveVerb, [IV]) :- intransitiveVerb(IV).
rule(transitiveVerb, [TV]) :- transitiveVerb(TV).

article(a).
article(an).
article(the).
adjective(lazy).
adjective(excited).
adjective(trinocular).
adjective(rans).
properNoun(zach).
properNoun(ran).
properNoun(turing).
noun(spam).
noun(spampede).
noun(alien).
noun(donut).
noun(tofu).
noun(chinchilla).
intransitiveVerb(sleeps).
intransitiveVerb(runs).
intransitiveVerb(ran).
transitiveVerb(defeats).
transitiveVerb(eats).
transitiveVerb(overwhelms).