JESS: Can't use funcalls in backchained patterns?

Hi,

I was trying to make a rule that fires a few seconds after a fact is
asserted. Here is my experiment:

(deftemplate time (slot when))
(do-backward-chaining time)

(defrule do-time
    (need-time (when ?w))
    =>
    (schedule-time-alert ?w) )

(deftemplate k
    (slot when (default-dynamic (call System currentTimeMillis))) )

(defrule r
    (k (when ?w))
    (time (when =(+ ?w 3000)))   ; a time fact 3 seconds after k is expected
    =>
    (printout t "3 seconds after k!" crlf) )

Function schedule-time-alert is implemented in Java and is supposed to
add a fact at the indicated time.
While this approach looks pretty clean to me, it does not even compile.
I am getting a "Can't use funcalls in backchained patterns when", in
rule r. This does not seem to be documented (at least I did not find it).

There is a work arround described in
http://www.jessrules.com/jess/FAQ.shtml#Q9
That approach has been suggested in previous e-mail threads, I have noticed.
But while it seems to work, it is also much more CPU-intensive, as a
number of time events (idle facts in faq Q9) would be added for no reason.

Any thoughts?

Thanks.

Henrique



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