Re: JESS: Can't use funcalls in backchained patterns?

This is quite clever, but as you found, this won't work due to  
limitations in the implementation. But you could skip backward  
chaining altogether and just do something like

(defrule r
    (k (when ?w&:(progn (schedule-time-alert (+ ?w 3000)) TRUE)))
    (time (when =(+ ?w 3000)))   ; a time fact 3 seconds after k is  
expected
    =>
    (printout t "3 seconds after k!" crlf) )

You would not need the progn/TRUE if schedule-time-alert returned a  
true value.


On Jul 21, 2010, at 5:59 AM, Henrique Lopes Cardoso wrote:

> 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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Ernest Friedman-Hill
Informatics & Decision Sciences          Phone: (925) 294-2154
Sandia National Labs
PO Box 969, MS 9012                            [email protected]
Livermore, CA 94550                             http://www.jessrules.com





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