How do you define an operator in prolog to make a list?

Question

I want to define an operator "++>" in a way so that typing "a ++> b" will make a list of [a,b].

I've written the following code, but it doesn't appear to do the job.

++>(X,Y) :-
 [X,Y].

:- op(500,xfy,++>).

Answer 1

Does this work for you:

++>((X,Y),Z) :-Z= [X,Y].

:- op(500,xfy,++>).

Answer 2

[a,b,c] is just syntactic sugar for '.'(a,'.'(b,'.'(c)))) . So you may define your operator just the same and write a conversion predicate:

:- op(500,xfy,'++>').

convert('++>'(A,B),[A|R]) :-
    convert(B,R).
convert(Any,[Any]).

Example:

| ?- X = 1++>2++>3, convert(X,Y).                                    
X = 1++>2++>3
Y = [1,2,3] ?
yes

Answer 3

:- op(500,xfy,++>).
++>(X,Y,[X,Y]).

And use it like

?- ++>(1,2,X).
X = [1, 2].

Actually, Prolog is not oriented calculations, so operators is just synonyms to the terms. You want a term\\3, where one element is list of two another. So, you can't use 2-placed operator in that case. Btw, you can't use is in this situation, because it used only in arithmetic cases.