10.38.4.7 Code of the Built-In Visualizers

Now that you know everything about writing visualizers, it might be worth having a look at the code of the built-in visualizers, fdbg_show/2 and fdbg_label_show/3.

     fdbg_show(Constraint, Actions) :-
             fdbg_annotate(Constraint, Actions, AnnotC, CVars),
             print(fdbg_output, AnnotC),
             nl(fdbg_output),
             fdbg_legend(CVars, Actions),
             nl(fdbg_output).
     
     fdbg_label_show(start, I, Var) :-
             fdbg_annotate(Var, AVar, _),
             (   AVar = fdvar(Name, _, Set)
             ->  fdset_to_range(Set, Range),
                 format(fdbg_output,
                        'Labeling [~p, <~p>]: starting in range ~p.~n',
                        [I,Name,Range])
             ;   format(fdbg_output,
                        'Labeling [~p, <>]: starting.~n',
                        [I])
             ).
     fdbg_label_show(fail, I, Var) :-
             (   var(Var)
             ->  lookup_or_set_name(Var, Name),
                 format(fdbg_output,
                        'Labeling [~p, <~p>]: failed.~n~n',
                        [I,Name])
             ;   format(fdbg_output,
                        'Labeling [~p, <>]: failed.~n~n',
                        [I])
             ).
     fdbg_label_show(step(Step), I, Var) :-
             (   var(Var)
             ->  lookup_or_set_name(Var, Name),
                 format(fdbg_output,
                        'Labeling [~p, <~p>]: ~p~n~n',
                        [I,Name,Step])
             ;   format(fdbg_output,
                        'Labeling [~p, <>]: ~p~n~n',
                        [I,Step])
             ).
     
     lookup_or_set_name(Term, Name) :-
             fdbg_get_name(Term, Name), !.
     lookup_or_set_name(Term, Name) :-
             fdbg_assign_name(Term, Name).

As you can see, they are quite simple, thanks to the extensive set of support predicates also available to the user.