Prolog Querying: Unifying a variable in a nested compund Term

Question

I have a set of Prolog facts which I am attempting to query, but I am having trouble figuring out how to unify variables that are more deeply nested. An example of a fact in the database is as follows:

character(super,mario, type(human)).
character(donkey,kong, type(ape)).

videogame(year(1991), console(nintendo), title([super,mario,bros]), characters([character(super,mario), character(princess,peach)])).
videogame(year(1999), console(nintendo), title([super,smash,bros]), characters([character(super,mario), character(donkey,kong)])).

So for example, I want to query which characters appear in more than 1 video game. So I know that I want to create two instances of videogame and ensure that the same character appears (by name) in both games, and that those games are not the same game (by title).

Thus I would do something like:

?- videogame(_, _, title(Title1), characters(?????)), videogame(_, _, title(Title2), characters(?????)), not(Title1 == Title2).

However, my issue has been finding a way to create variables within the characters portion such that the "first" and "last" name of the characters unifies with a character that appears in more than one videogame.

I have tried things along the lines of the following (to fill in the question marks above in the full query) to try and unify the first and last name of the character, but they produce the error:

characters(character[First,Last])
characters([First, Last])


 ERROR: Syntax error: Operator expected

I have also tried the following, which just returns false.

?- videogame(_, _, title(Title1), _), videogame(_, _, title(Title2), _), member(actor(First,Last,_), cast), not(Title1 == Title2).

I would appreciate some help so that I can gain a better understanding of how query in Prolog even in the presence of more nested terms.

@LuaiGhunim I am aware it is in list structure, although I have the titles put into this structure in the database. I am more concerned with the querying of these lists, in particular the characters list because it is the most nested. — MastRofDsastR
@LuaiGhunim Sorry for the confusion of that portion, I have it acting in a first name, last name fashion where super = first name and mario = last name, but it is one character. So I want the first and last name to unify for the character to be considered in more than 1 video game. — MastRofDsastR
Every clause has to end with at .. That's the reason for the errors. — false

CapelliC CapelliC · Accepted Answer · 2017-11-25T22:17:11

with intersection/3 from library(lists) I would write

?- videogame(_,_,title(Title1),characters(Cs1)), videogame(_,_,title(Title2),characters(Cs2)), Title1 @< Title2, intersection(Cs1,Cs2,Common).

Prolog Querying: Unifying a variable in a nested compund Term

1 Answers