Creating a new variable withing prolog program

Question

I have a question regarding the variable creating inside the program. Lets say i have a function(?- not sure about the wording here), which is /2, is there a way of changing it to /1?

:- use_module(library(clpfd)).
solve(N, L):-
        L = [A,B,C,D],
        L ins 1..sup,
        N #= A * B * C * D,
        all_distinct(L),
        A #< B, B #< C, C #< D,
        labeling([],L),nl,
        Z #= A+B+C+D,
        write(A+B+C+D=Z).

Is there a possibility of actually making it solve(N), where L is created on the run. Tried using both,

L is [A,B,C,D],

or

L = [],
L is [A,B,C,D]

but no luck right now.

Program is working like that:->

 ?- solve(30,Elements).

1+2+3+5=11
Elements = [1, 2, 3, 5].

?-     solve(60, Elements).

1+2+3+10=16
Elements = [1, 2, 3, 10] ;

1+2+5+6=14
Elements = [1, 2, 5, 6] ;

1+3+4+5=13
Elements = [1, 3, 4, 5] ;
false.

Answer 1

Yes but then you would get for example:

?- solve(30).

1+2+3+5=11
true.

?- solve(60).

1+2+3+10=16
true ;

1+2+5+6=14
true ;

1+3+4+5=13
true ;
false.

If this is what you are looking for just write solve(N) instead solve(N, L):

:- use_module(library(clpfd)).
solve(N):-
        L = [A,B,C,D],
        L ins 1..sup,
        N #= A * B * C * D,
        all_distinct(L),
        A #< B, B #< C, C #< D,
        labeling([],L),nl,
        Z #= A+B+C+D,
        write(A+B+C+D=Z).

Keep in mind that L is [A,B,C,D] is not valid because is/1 is used for arithmetic expressions not unification. You need to use =/2 which unifies L with a four element list.

If you want to print the list you could write:

:- use_module(library(clpfd)).
solve(N):-
        L = [A,B,C,D],
        L ins 1..sup,
        N #= A * B * C * D,
        all_distinct(L),
        A #< B, B #< C, C #< D,
        labeling([],L),nl,
        Z #= A+B+C+D,

        writeln(A+B+C+D=Z),
        write("Elements="),
        write(L).

Example:

?- solve(30).

1+2+3+5=11
Elements=[1,2,3,5]
true.