How to force clips to ignore a certain fact for a rule? - clips

Question

I have the following deftemplate
(deftemplate potential
(multislot values (type INTEGER))
)
and I want to remove instances of this deftemplate if an integer only occurs in it.
Example:
fact-1: potential 1 2 3
fact-2: potential 2 3 4
fact-3: potential 2 3 4 5
I want to retract fact-1 and fact-3 because they include 1 and 5 uniquely.
I'm trying to achieve it using a rule like the following:
1 (defrule remove_if_only_option
2 ?p<-(potential (values $? ?value $? ))
3 (not (exists (potential (values $? ?value $?) )))
4 =>
5 (retract ?p)
7 )
Obviously it doesn't work as line 3 can match the initial fact. Is there any way to make this run in such a way the rule doesn't consider ?p for the rest of it?
Thanks.

Answer 1

Neither of the patterns in your rule will be effected by the presence or absence of the initial-fact since they both match potential facts. The exists conditional element is superfluous in the second pattern, so your rule is equivalent to
(defrule remove_if_only_option
?p <- (potential (values $? ?value $?))
(not (potential (values $? ?value $?)))
=>
(retract ?p))
and since the condition x and not x is never true, this rule can never be satisfied.
You can tell if two facts of the same type are different by comparing their fact address, but since you can't bind a fact address within a not conditional element, you can't do that in this case. Alternatively, you can include a slot containing a unique value for each fact that can be used to tell if the facts are different:
CLIPS (6.31 6/12/19)
CLIPS>
(deftemplate potential
(slot id (default-dynamic (gensym*)))
(multislot values (type INTEGER)))
CLIPS>
(defrule remove_if_only_option
?p <- (potential (id ?id) (values $? ?value $?))
(not (potential (id ~?id) (values $? ?value $?)))
=>
(retract ?p))
CLIPS>
(assert (potential (values 1 2 3))
(potential (values 2 3 4))
(potential (values 2 3 4 5)))
<Fact-3>
CLIPS> (agenda)
0 remove_if_only_option: f-3,*
0 remove_if_only_option: f-1,*
For a total of 2 activations.
CLIPS>
Initially, this appears to work, but once it runs you can see there are issues:
CLIPS> (run 1)
CLIPS> (agenda)
0 remove_if_only_option: f-2,*
0 remove_if_only_option: f-1,*
For a total of 2 activations.
CLIPS>
Once f-3 is removed, the value 4 in f-2 now becomes unique and so this fact will now also be removed by this rule. The problem is that the common set of values is implicitly represented by the collection of potential facts, and once you start removing them you're altering the common set of values.
In order to do this, you'll need at least two steps and consequently at least two rules. One way to do it is to mark the facts that need to be deleted in one step and then delete them in another:
CLIPS> (clear)
CLIPS>
(deftemplate potential
(slot id (default-dynamic (gensym*)))
(multislot values (type INTEGER))
(slot delete (default no)))
CLIPS>
(defrule remove_if_only_option
(not (done))
?p <- (potential (id ?id) (values $? ?value $?) (delete no))
(not (potential (id ~?id) (values $? ?value $?)))
=>
(modify ?p (delete yes)))
CLIPS>
(defrule remove
(declare (salience -10))
?p <- (potential (delete yes))
=>
(assert (done))
(retract ?p))
CLIPS>
(assert (potential (values 1 2 3))
(potential (values 2 3 4))
(potential (values 2 3 4 5)))
<Fact-3>
CLIPS> (agenda)
0 remove_if_only_option: *,f-3,*
0 remove_if_only_option: *,f-1,*
For a total of 2 activations.
CLIPS> (run 1)
CLIPS> (agenda)
0 remove_if_only_option: *,f-1,*
-10 remove: f-4
For a total of 2 activations.
CLIPS> (facts)
f-0 (initial-fact)
f-1 (potential (id gen4) (values 1 2 3) (delete no))
f-2 (potential (id gen5) (values 2 3 4) (delete no))
f-4 (potential (id gen6) (values 2 3 4 5) (delete yes))
For a total of 4 facts.
CLIPS> (run 1)
CLIPS> (agenda)
-10 remove: f-5
-10 remove: f-4
For a total of 2 activations.
CLIPS> (run)
CLIPS> (facts)
f-0 (initial-fact)
f-2 (potential (id gen5) (values 2 3 4) (delete no))
f-6 (done)
For a total of 3 facts.
CLIPS>
Another way to create a fact containing the unique values:
CLIPS> (clear)
CLIPS>
(deftemplate potential
(slot id (default-dynamic (gensym*)))
(multislot values (type INTEGER)))
CLIPS>
(defrule add-to-unique
(not (done))
?c <- (unique $?unique)
(potential (id ?id) (values $? ?value $?))
(not (potential (id ~?id) (values $? ?value $?)))
(test (not (member$ ?value ?unique)))
=>
(retract ?c)
(assert (unique $?unique ?value)))
CLIPS>
(defrule remove_if_only_option
(declare (salience -10))
(unique $?unique)
?p <- (potential (values $? ?value $?))
(test (member$ ?value ?unique))
=>
(assert (done))
(retract ?p))
CLIPS>
(assert (potential (values 1 2 3))
(potential (values 2 3 4))
(potential (values 2 3 4 5)))
<Fact-3>
CLIPS> (assert (unique))
<Fact-4>
CLIPS> (run)
CLIPS> (facts)
f-0 (initial-fact)
f-2 (potential (id gen26) (values 2 3 4))
f-6 (unique 5 1)
f-7 (done)
For a total of 4 facts.
CLIPS>