Prolog search by same field in list

Question

I have DB with those structure

        my_family( person("FN","SN", unempl(), 20), 
                    person("FN2","SN", work("Soft", 200), 30), 
                    [person("FN3","SN", work("HP" , 10), 13), 
                    person("FN4","SN", work("LP", 200), 1), 
                    person("FN5","SN" , work("qwerty", 300), 1)]).

 domains
    family = person*.
    person = person(string Name, string LastName, work, integer Age).
    work = work(string Corp, real Salary)

How do I get the family, with children's same age?

I try

 clauses
    length_of([], 0).
    length_of([_|T], L):-
        length_of(T, TailLength),
        L = TailLength + 1.

    ....

        my_family(person(_, _, _, FA), person(_, _, _, MA), Child),


        getName(Child).

        getName([]).
        getName([person(N, S, _, AC)|T]):-
            findall(1, _=person(_, S, _, AC), L),
            length_of(L, LN),
            2 <= LN,
            stdIO::writef("Family: %\n\n\n", S),
            getName(T).

But it does not work, it seems that findall returns a list L with only one element.

Answer 1

I think you should drop AC in findall

findall(1, _=person(_, S, _, _), L),

otherwise the list is constrained to people with the very same age of current person. Disclaimer: I can't test that code, and the syntax it's very out of standard: in ISO Prolog, findall/3 works without the _=person(...), but that could be a feature of Visual prolog unknown to me