:-export(demo_nb_linkval/1). demo_nb_linkval(T) :- T = nice(N), ( N = world, nb_linkval(myvar, T), fail ; nb_getval(myvar, V), writeln(V) ).

:- dynamic(sk_out/1).

q :- q(X), writeln(X). q(X) :- '$depth_of_var'(X, D), format('Depth = ~w~n', [D]), D < 5, q(X),notail.

notail.

/* Running this says:

1 ?- q. Depth = 1 Depth = 2 Depth = 3 Depth = 4 Depth = 5

*/