Showing Selected Constraints (advanced version)

Suppose that you want to give the constraints that you are interested in as an argument to the visualizer, instead of defining them in a table. The following visualizer implements this.

     :- use_module(library(lists), [append/3]).
     
     %% filter_events(+CtrSpecs, +Constraint, +Actions):  This predicate will
     %%   only show constraint events if they match an element in the list CtrSpecs,
     %%   or if CtrSpecs is wrapped in -/1, then all the non-matching events will
     %%   be shown.
     %%   CtrSpecs can contain the following types of elements:
     %%     ctr_name             - matches all constraints of the given name
     %%     ctr_name/arity       - matches constraints with the given name and arity
     %%     ctr_name(...args...) - matches constraints unifyable with the given term
     %%
     %%   For the selected events fdbg_show(Constraint, Actions) is called.
     %%
     %%   This visualizer can be specified when turning fdbg on, e.g.:
     %%     fdbg_on([constraint_hook(filter_events([count/4]))]).
     %%   or
     %%     fdbg_on([constraint_hook(filter_events(-[in_set]))]).
     filter_events(CtrSpecs, Constraint, Actions) :-
             filter_events(CtrSpecs, fdbg_show, Constraint, Actions).
     
     %% filter_events(+CtrSpecs, +Visualizer, +Constraint, +Actions):  Same as
     %%   the above predicate, but the extra argument Visualizer specifies the
     %%   predicate to be called for the selected events (in the same form as
     %%   in the constraint_hook option, i.e. without the last two arguments).
     %%
     %%   For example:
     %%     fdbg_on([constraint_hook(filter_events([count/4],my_show))]).
     filter_events(-CtrSpecs, Visualizer, Constraint, Actions) :- !,
             \+ show_constraint(CtrSpecs, Constraint),
             add_args(Visualizer, [Constraint, Actions], Goal),
             call(Goal).
     filter_events(CtrSpecs, Visualizer, Constraint, Actions) :-
             show_constraint(CtrSpecs, Constraint),
             add_args(Visualizer, [Constraint, Actions], Goal),
             call(Goal).
     
     show_constraint([C|_], Constraint) :-
             matches(C, Constraint), !.
     show_constraint([_|Cs], Constraint) :-
             show_constraint(Cs, Constraint).
     
     matches(Name/Arity, Constraint) :- !,
             functor(Constraint, Name, Arity).
     matches(Name, Constraint) :-
             atom(Name), !,
             functor(Constraint, Name, _).
     matches(C, Constraint) :-
             C = Constraint.
     
     add_args(Goal0, NewArgs, Goal) :-
             Goal0 =.. [F|Args0],
             append(Args0, NewArgs, Args),
             Goal =.. [F|Args].
     

Here is a session using the visualizer, filtering out everything but all_different/1 constraints:

     | ?- [library('clpfd/examples/suudoku')].
     [...]
     | ?- fdbg_on(constraint_hook(filter_events([all_different/1]))).
     % The clp(fd) debugger is switched on
     yes
     % advice
     | ?- suudoku([], 1, P).
     all_different([1,<fdvar_1>,<fdvar_2>,8,<fdvar_3>,
                    4,<fdvar_4>,<fdvar_5>,<fdvar_6>])
         fdvar_1 = 1..9 -> (2..3)\/(5..7)\/{9}
         fdvar_2 = 1..9 -> (2..3)\/(5..7)\/{9}
         fdvar_3 = 1..9 -> (2..3)\/(5..7)\/{9}
         fdvar_4 = 1..9 -> (2..3)\/(5..7)\/{9}
         fdvar_5 = 1..9 -> (2..3)\/(5..7)\/{9}
         fdvar_6 = 1..9 -> (2..3)\/(5..7)\/{9}
     
     [...]
     
     all_different([7,6,2,5,8,4,1,3,9])
         Constraint exited.
     
     P = [...] ;
     no
     % advice
     | ?- fdbg_off.
     % The clp(fd) debugger is switched off
     yes
     

In the next session, all constraints named all_different are ignored, irrespective of arity. Also, we explicitly specified the visualizer to be called for the events which are kept (here, we have written the default, fdbg_show, so the actual behavior is not changed).

     | ?- [library('clpfd/examples/suudoku')].
     [...]
     | ?- fdbg_on(constraint_hook(filter_events(-[all_different],fdbg_show))).
     % The clp(fd) debugger is switched on
     yes
     % advice
     | ?- suudoku([], 1, P).
     domain([1,<fdvar_1>,<fdvar_2>,8,<fdvar_3>,
             4,<fdvar_4>,<fdvar_5>,<fdvar_6>],1,9)
         fdvar_1 = inf..sup -> 1..9
         fdvar_2 = inf..sup -> 1..9
         fdvar_3 = inf..sup -> 1..9
         fdvar_4 = inf..sup -> 1..9
         fdvar_5 = inf..sup -> 1..9
         fdvar_6 = inf..sup -> 1..9
         Constraint exited.
         Constraint exited.
     
     [...]
     
     domain([2,<fdvar_46>,5,<fdvar_47>,<fdvar_48>,
            <fdvar_49>,<fdvar_50>,<fdvar_51>,9],1,9)
         fdvar_46 = inf..sup -> 1..9
         fdvar_47 = inf..sup -> 1..9
         fdvar_48 = inf..sup -> 1..9
         fdvar_49 = inf..sup -> 1..9
         fdvar_50 = inf..sup -> 1..9
         fdvar_51 = inf..sup -> 1..9
         Constraint exited.
     
     P = [...] ;
     no
     % advice
     | ?- fdbg_off.
     % The clp(fd) debugger is switched off
     yes
     

In the last session, we specify a list of constraints to ignore, using a pattern to select the appropriate constraints. Since all constraints in the example match one of the items in the given list, no events are printed.

     | ?- [library('clpfd/examples/suudoku')].
     [...]
     | ?- fdbg_on(constraint_hook(filter_events(-[domain(_,1,9),all_different(_)]))).
     % The clp(fd) debugger is switched on
     yes
     % advice
     | ?- suudoku([], 1, P).
     P = [...] ;
     no
     % advice
     | ?- fdbg_off.
     % The clp(fd) debugger is switched off