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Prolog++ programs

Prolog++ is a product by LPA Associates for object-oriented programming extensions of LPA Prolog. Most Prolog++ programs can be easily converted into SICStus Objects programs. The following is a translation of a program for fault diagnosis in LPA's Prolog++ manual, page 83. The program illustrates a top-down diagnosis method starting from general objects to more specific objects. The problem is fault diagnosis for car maintenance. The objects have the following structure:

- faults
        - electrical
        |       - lights
        |       - starting
        |               - starter_motor
        |               - sparking
        |                       - plugs
        |                       - distributer
        - fuel_system
        - mechanical

The general diagnosis method is defined in the object faults, whereas the cause-effect relationships are defined in the specific objects e.g. the object distributor.

This program heavily uses the sub/1 method. We have tried to be as close as possible to the original formulation.

faults :: {

        super(utility) &
        dynamic(told/2) &

        /* no fault is the default */
        fault(_, _) :- :fail &

        findall :-
                <: restart,
                :: sub(Sub),
                Sub :: find(Where, Fault),
                <: print(Where, Fault),
                :fail &
        findall &

        print(Where, Fault) :-
                :writeseqnl('Location       : ', [Where]),
                :writeseqnl('Possible Fault : ', [Fault]),
                :nl &

        find(Where, Fault) :-
                self(Where),
                fault(FaultNum, Fault),
                \+ (effect(FaultNum, S),
                    contrary(S, S1),
                    exhibited(S1)
                   ),
                \+ (effect(FaultNum, SymptomNum),
                    \+ exhibited(SymptomNum)) &

        find(Where, Fault) :-
                sub(Sub),
                Sub :: find(Where, Fault) &

        exhibited(S) :-
                :: told(S, R), !,
                R = yes &
        exhibited(S) :-
                symptom(S,Text),
                (   :yesno([Text]) -> R = yes
                ;   R = no
                ),
                :: asserta(told(S,R)),
                R = yes &

        restart :-
                :: retractall(told(_,_))

        }.
electrical :: {
        super(faults)
        }.

fuel_system :: {
        super(faults)
        }.

mechanical :: {
        super(faults)
        }.

lights :: {
        super(electrical)
        }.

sparking :: {
        super(electrical)
        }.

starting :: {
        super(electrical)
        }.

starter_motor :: {
        super(electrical)
        }.

plugs :: {
        super(sparking)
        }.

engine :: {
        super(mechanical)
        }.

cylinders :: {
        super(engine)
        }.
distributor :: {
        super(sparking) &

        /* faults */
        fault('F1001', 'Condensation in distributor cap') &
        fault('F1002', 'Faulty distributor arm') &
        fault('F1003', 'Worn distributor brushes') &

        /* symptoms */
        symptom('S1001', 'Starter turns, but engine does not fire') &
        symptom('S1002', 'Engine has difficulty starting') &
        symptom('S1003', 'Engine cuts out shortly after starting') &
        symptom('S1004', 'Engine cuts out at speed') &

        /* symptoms contrary to each other */
        contrary('S1002', 'S1001') &
        contrary('S1003', 'S1001') &

        /* causal-effect relationship */
        effect('F1001', 'S1001') &
        effect('F1002', 'S1001') &
        effect('F1002', 'S1004') &
        effect('F1003', 'S1002') &
        effect('F1003', 'S1003')

        }.

yesno(Value) :- write(Value), nl, read(yes).

writeseqnl(Prompt, L) :- write(Prompt), write_seq(L).

write_seq([]).
write_seq([X|L]) :- write(X), write(' '), write_seq(L), nl.

faults :- faults :: findall.
| ?- faults.
[Starter turns, but engine does not fire]
|: yes.
Location       : distributor
Possible Fault : Condensation in distributor cap

[Engine cuts out at speed]
|: yes.
Location       : distributor
Possible Fault : Faulty distributor arm

| ?- faults.
[Starter turns, but engine does not fire]
|: no.
[Engine has difficulty starting]
|: yes.
[Engine cuts out shortly after starting]
|: yes.
Location       : distributor
Possible Fault : Worn distributor brushes