How to debug clpfd programs?

Question

I have a program in SICStus Prolog (clpfd) and I would like to see what is going on during labeling. I tried trace but it is too verbose which makes it hard to understand what is really going on (what values are assigned to which variables, how are the constraints propagated, etc.).

A shortened version of my program:

runTT(Goal) :- 

    PLST_1 in {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59},
    DLST_1 in {0, 1, 2, 3, 4},
    DLST_1 #= PLST_1 / 12,
    % T: Bo, S: A, D: 1
    PLST_2 in {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59},
    DLST_2 in {0, 1, 2, 3, 4},
    DLST_2 #= PLST_2 / 12,
    Domain__I0_01_0 in 0..1, Domain__I0_01_1 in 0..1, Domain__I0_01_2 in 0..1, Domain__I0_01_3 in 0..1, Domain__I0_01_4 in 0..1, Domain__I0_01_5 in 0..1, Domain__I0_01_6 in 0..1, Domain__I0_01_7 in 0..1, Domain__I0_01_8 in 0..1, Domain__I0_01_9 in 0..1, Domain__I0_01_10 in 0..1, Domain__I0_01_11 in 0..1, Domain__I0_01_12 in 0..1, Domain__I0_01_13 in 0..1, Domain__I0_01_14 in 0..1, Domain__I0_01_15 in 0..1, Domain__I0_01_16 in 0..1, Domain__I0_01_17 in 0..1, Domain__I0_01_18 in 0..1, Domain__I0_01_19 in 0..1, Domain__I0_01_20 in 0..1, Domain__I0_01_21 in 0..1, Domain__I0_01_22 in 0..1, Domain__I0_01_23 in 0..1, Domain__I0_01_24 in 0..1, Domain__I0_01_25 in 0..1, Domain__I0_01_26 in 0..1, Domain__I0_01_27 in 0..1, Domain__I0_01_28 in 0..1, Domain__I0_01_29 in 0..1, Domain__I0_01_30 in 0..1, Domain__I0_01_31 in 0..1, Domain__I0_01_32 in 0..1, Domain__I0_01_33 in 0..1, Domain__I0_01_34 in 0..1, Domain__I0_01_35 in 0..1, Domain__I0_01_36 in 0..1, Domain__I0_01_37 in 0..1, Domain__I0_01_38 in 0..1, Domain__I0_01_39 in 0..1, Domain__I0_01_40 in 0..1, Domain__I0_01_41 in 0..1, Domain__I0_01_42 in 0..1, Domain__I0_01_43 in 0..1, Domain__I0_01_44 in 0..1, Domain__I0_01_45 in 0..1, Domain__I0_01_46 in 0..1, Domain__I0_01_47 in 0..1, Domain__I0_01_48 in 0..1, Domain__I0_01_49 in 0..1, Domain__I0_01_50 in 0..1, Domain__I0_01_51 in 0..1, Domain__I0_01_52 in 0..1, Domain__I0_01_53 in 0..1, Domain__I0_01_54 in 0..1, Domain__I0_01_55 in 0..1, Domain__I0_01_56 in 0..1, Domain__I0_01_57 in 0..1, Domain__I0_01_58 in 0..1, Domain__I0_01_59 in 0..1,
    global_cardinality([ PLST_1, PLST_2, PLST_3 ], [0-Domain__I0_01_0, 1-Domain__I0_01_1, 2-Domain__I0_01_2, 3-Domain__I0_01_3, 4-Domain__I0_01_4, 5-Domain__I0_01_5, 6-Domain__I0_01_6, 7-Domain__I0_01_7, 8-Domain__I0_01_8, 9-Domain__I0_01_9, 10-Domain__I0_01_10, 11-Domain__I0_01_11, 12-Domain__I0_01_12, 13-Domain__I0_01_13, 14-Domain__I0_01_14, 15-Domain__I0_01_15, 16-Domain__I0_01_16, 17-Domain__I0_01_17, 18-Domain__I0_01_18, 19-Domain__I0_01_19, 20-Domain__I0_01_20, 21-Domain__I0_01_21, 22-Domain__I0_01_22, 23-Domain__I0_01_23, 24-Domain__I0_01_24, 25-Domain__I0_01_25, 26-Domain__I0_01_26, 27-Domain__I0_01_27, 28-Domain__I0_01_28, 29-Domain__I0_01_29, 30-Domain__I0_01_30, 31-Domain__I0_01_31, 32-Domain__I0_01_32, 33-Domain__I0_01_33, 34-Domain__I0_01_34, 35-Domain__I0_01_35, 36-Domain__I0_01_36, 37-Domain__I0_01_37, 38-Domain__I0_01_38, 39-Domain__I0_01_39, 40-Domain__I0_01_40, 41-Domain__I0_01_41, 42-Domain__I0_01_42, 43-Domain__I0_01_43, 44-Domain__I0_01_44, 45-Domain__I0_01_45, 46-Domain__I0_01_46, 47-Domain__I0_01_47, 48-Domain__I0_01_48, 49-Domain__I0_01_49, 50-Domain__I0_01_50, 51-Domain__I0_01_51, 52-Domain__I0_01_52, 53-Domain__I0_01_53, 54-Domain__I0_01_54, 55-Domain__I0_01_55, 56-Domain__I0_01_56, 57-Domain__I0_01_57, 58-Domain__I0_01_58, 59-Domain__I0_01_59]),
    Goal = [PLST_1, PLST_2],
    labeling([], Goal).

Thanks for any hint!

Note: I would love to remove the "domain hell" as well but as far as I understand Prolog I cannot use one variable (e.g. Domain_01).

Answer 1

I've seen there is an ad hoc debugger, but I'm sorry I've never used it.

That apart, I tried the visualization of constraint solving, as suggested from Markus Triska, but, apart from requiring to modify the program, most probably it's a simple curiosity, not a real debugging tool.

SWI-Prolog debugger displays the constraint store (attributed variables) in a rather readable way. Because labeling is implemented in Prolog, I think should be possible - with pain - to follow the labeling process stepping inside library(clpfd) source.