dcgdemo.pl

english(X) :-
    phrase(sentence, X).

sentence --> sentence(_).
sentence(Number) -->
    noun_phrase(Number),
    verb_phrase(Number).

noun_phrase(Number) -->
    determiner(Number),
    noun(Number).

verb_phrase(Number) -->
    verb(Number),
    noun_phrase(Number).
verb_phrase(Number) -->
    verb(Number),
    sentence(Number).

determiner(singular) --> [a].
determiner(singular) --> [the].
determiner(plural) --> [].

noun(singular) -->
    [empire],
    [state],
    [building].
noun(plural) -->
    [Noun],
    {
        phrase(noun(singular), [Singular]),
        atom_concat(Singular, s, Noun)
    }.
noun(singular) --> [cat].
noun(plural) --> [cats].
noun(singular) --> [mouse].
noun(plural) --> [mice].


verb(singular) --> [scares].
verb(plural) --> [scare].
verb(singular) --> [hates].
verb(plural) --> [hate].


foo(X, Y) :-
    bar(X, A),
    blah(A, B),
    baz(B, Y).

foo -->
    bar,
    blah,
    baz.

bar(X,X).
blah(X,X).
baz(X,X).