Don't bother. I found the answer already: "accumulate"



How can I make Jess keep track of changes in working memory with respect to 
query-results automatically?
For example:
I have the following code:

(watch all)

(deftemplate fact (slot id))
(defquery countfacts (fact (id ?id)))

(defrule exec
  (test (> (count-query-results countfacts) 2))
  (printout t "There are more than 2 facts in WM." crlf)

(defrule firstfact
  (not (fact (id ?id)))
  (assert (fact (id 1)))

(defrule nextfact
  (fact (id ?id&:(< ?id 3)))
  (assert (fact (id (+ ?id 1))))


The rule 'exec' will not fire without a prior conditional-element (like (fact) 
), because the query is evaluated once, directly after reset, before new facts 
are asserted, and is not reevaluated when more facts become available, unless 
the rule has a reason to reevaluate the query by adding the extra condition.

Is it possible to have Jess reevaluate aggregate functions like counts, sums 
and averages automatically without having to think about when it would be a 
convenient time or status to evaluate a query? (I am aware of the performance 
issues this might cause).


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