Infinite loop inference Prolog

Question

An infinite loop is generated when the inferential motor is activated to make the necessary inferences.

The rules and facts have been defined according to a specific syntax for the meta-interpreter I am using.

The rule is a quintuple in which the second field is the consequence of the rule while the third field are the conditions for activating a rule.

The cycle is caused by the updating of the id (I1) through the term nextID, which I used to make sure that each assert the id is incremented This is my knowledge base:

Rules:

rule(1,[gn(Name,Surname,I1),retract(nextID(I)),nextID(I1)],
and([person(Name,Surname),nextID(I),call_p(I1 is I+1),Name=='john']),1,1).

Facts:

fact(1,nextID(0),1).
fact(2,person(john,black),1).

How should I modify the rule in such a way that the infinite loop is not created?

Answer 1

From your description of the rule fields, I would expect a different formulation for that rule:

rule(
    1,
    [retract(nextID(I)), call_p(I1 is I+1), assertz(nextID(I1), gn(Name,Surname,I1)], 
    and([person(Name,Surname), Name == 'john']),
    1,
    1
).

This would be equivalent to:

IF
    person(Name,Surname), Name == 'john'
THEN
    retract(nextID(I)), call_p(I1 is I+1),
    assertz(nextID(I1), gn(Name,Surname,I1)

But it's hard to tell exactly without knowing the details of your rule engine.

Update

Given the formulation of facts, notably fact(1,nextID(0),1), I wouldn't expect, however, that the embedded calls to retract/1 and assertz/1 would work. Isn't call_p/1 the escape mechanism to call Prolog goals from rules?