I have DCG sentences with two persons, representing a male and a female. I want to refer to the person metioned in a previous sentence using "he" or "she".
Suppose we have these DCGs:
father --> [Peter].
mother --> [Isabel].
child --> [Guido].
child --> [Claudia].
verb --> [is].
relation --> [father, of].
relation --> [mother, of].
pronoun --> [he].
pronoun --> [she].
adjective --> [a, male].
adjective --> [a, female].
s --> father, verb, relation, child.
s --> mother, verb, relation, child.
s --> pronoun, verb, adjective.
Querying ?- s([Peter, is, father, of, Guido], []). returns true.
How can I make sure that when I query now for ?- s([he, is, a, male], []). should return true only because I already mentioned Peter (a male) in the previous sentence. Otherwise it should return false.
This question uses the same example as here.
You can augment your DCG to keep some state (the gender of the last sentence):
father --> ['Peter'].
mother --> ['Isabel'].
child --> ['Guido'].
child --> ['Claudia'].
verb --> [is].
relation --> [father, of].
relation --> [mother, of].
pronoun(he) --> [he].
pronoun(she) --> [she].
adjective --> [a, male].
adjective --> [a, female].
s(G) --> s(none,G).
s(_,he) --> father, verb, relation, child.
s(_,she) --> mother, verb, relation, child.
s(G,G) --> pronoun(G), verb, adjective.
And now you can chain queries using this state:
?- phrase(s(G1),['Peter', is, father, of, 'Guido']), phrase(s(G1,G2),[he, is, a, male]).
G1 = G2, G2 = he
You may want to modify a bit the DCG to constrain the relations (using the Gender parameter). For example you DCG currently accepts 'Peter' is mother of 'Guido' which I'm not sure was intended.