%---------------------------------------------------------------------------%
% vim: ts=4 sw=4 et ft=mercury
%---------------------------------------------------------------------------%

:- module same_length_2.
:- interface.
:- import_module list.

:- mode my_input_list_skel == list_skel >> list_skel.
:- mode my_output_list_skel == free >> list_skel.
:- mode my_list_skel_output == list_skel >> ground.

:- pred p is semidet.

:- pred p2(list(T)::my_output_list_skel) is nondet.

:- implementation.

:- pred q(list(T)::my_input_list_skel).
:- pred r(list(T)::my_output_list_skel).

q(_X) :-
    q([]).

r(X) :-
    r(X).

p :-
    r(X),
    q(X).

p2(X) :-
    (
        r(X),
        q(X)
    ;
        r(X),
        q(X)
    ).