;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; This fact will be used to sleep when idle
(deffacts idle-fact
(idle))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; This rule will always be on the agenda! Make the salience
;; lower than any other rule.
(defrule sleep-if-bored
(declare (salience -100))
?idle <- (idle)
=>
(retract ?idle)
(call java.lang.Thread sleep 100)
(assert (idle)))
This "idle rule" technique is useful in other contexts, too -- for
instance, as a way of updating a "timestamp" fact.
private Object m_activationSemaphore = new String("ACTIVATION LOCK");
Also have a look at the release notes in the development version of
Jess for news about any problems being addressed in new releases.
(defrule match-1 (item ?x) (item ?y) (item ?z) (item ?w) (find-match ?x ?y ?z ?w) => )is HORRIBLE, because it must form all possible permutations of 'item' facts before finding the one permutation that matches the 'find-match' fact. If there are 10 'item' facts, this is 10x10x10x10 = 10,000 partial matches are sent to the last join node - a lot of bookkeeping! If you rewrite the rule like this:
(defrule match-2 (find-match ?x ?y ?z ?w) (item ?x) (item ?y) (item ?z) (item ?w) => )Then there is precisely one partial match sent to the last join node - actually only one is sent to each join node. Whereas the first rule might take several minutes to reset on a slow machine, the second rule resets instantaneously. The jess (view) command can be used to explore the efficiency of your rules.
(defrule rule-1 (number ?x) (< ?x 3) => (printout t ?x " is less than 3." crlf))it won't work the way you expect. Instead of comparing ?x to 3, the line (< ?x 3) is a pattern that matches facts like (< 2 3) and (< 27 3). Since you probably don't have any such facts, this rule will never fire. If you want to write a pattern that consists solely of a function call, use the test CE.
(defrule rule-2 (number ?x) (test (< ?x 3)) => (printout t ?x " is less than 3." crlf))
(defrule rule-3 (number ?x) (not (< ?x 3)) => (printout t ?x " is not less than 3." crlf))the second pattern is true whenever there are no facts that look like (< 39 3). Since you probably don't have any such facts, this condition will always be met, and the rule will always fire. You can rewrite this with a test conditional element:
(defrule rule-4 (number ?x) (test (not (< ?x 3))) => (printout t ?x " is not less than 3." crlf))