Inspecting programs with attributed variables using clause/2

General
1

I have this code that uses library(clpBNR):

edge(T, A, B) :-
        seg(A1, B1),
        point(A,PA),
        point(B,PB),
        dist(A1, PA, T),
        dist(B1, PB, T).

dist(p(X1, Y1), p(X2, Y2), D) :-
% clpBNR constraint, X1/Y1/X2/Y2/D don't have to be ground
        { sqrt((X2 - X1)^2 + (Y2 - Y1)^2) =< D }.

seg(..., ...) % Not important, omitted for brevity
point(..., ...)

Now, when I try to get the body of edge/3 with clause/2 I get … silent death:

122 ?- listing(edge/3).
experiment_file:edge(T, A, B) :-
    seg(A1, B1),
    point(A, PA),
    point(B, PB),
    dist(A1, PA, T),
    dist(B1, PB, T).

true.

123 ?- clause(edge(A,B,C), Bod).
false.

Is this normal? Is there an alternative to clause/2 to get the body of a clause when there are attributed variables in one of the body goals?

2

Try ?- clause(experiment_file:edge(A,B,C), Bod). … listing/1 uses clause/2, so it should work. It is only more flexible to find what you are trying to list. I.e., if there is no module specified try in every module.

3

Not relevant to your problem, but there will be no attributes attached to any of the variables in the results of listing/1 or clause/2. They don’t get defined (via side effect) until dist/3 is actually called, and ?- listing(edge/3). won’t do that.