Thank you for your helpful replies. I guess the solution of extending
the antecedent of the rules with one fact that is asserted and retracted
before each run is more efficient than retracting and reasserting all facts?
I am implementing a prototype of a programming language with a
predefined semantics, it is difficult to explain why exactly I want this
behavior. Basically, most constructs translate naturally to Jess rules
that assert and retract facts. For those rules it is not a problem (it's
even convenient) that a rule only fires once, but one particular
construct requires to fire (and call a user-defined function) each time
its precondition is satisfied. I implemented this as rules of the form:
(defrule myrule (precondition) => (function params))
Nick.
Wolfgang Laun wrote:
The following function retracts and reasserts all facts in the engine.
Except for the fact ids, the working memory should be the same after
the call, but all rules will fire over again.
(deffunction rewind ()
(bind ?e (engine))
(bind ?it (?e listFacts))
(while (?it hasNext)
(bind ?fact (?it next))
(?e assertFact (?e retract ?fact) )
)
)
-W
On Thu, Jul 23, 2009 at 4:22 PM, Ernest Friedman-Hill
<[email protected] <mailto:[email protected]>> wrote:
I can't think of any other way to achieve that behavior, so I
guess you can go ahead and do it. You might tell us *why* you want
that behavior, though, because maybe there's another solution.
On Jul 23, 2009, at 5:02 AM, [email protected] <mailto:[email protected]>
wrote:
Dear Jess users,
I have been looking in the manual and mailing list for some
time but
couldn't find an answer. Maybe you could help me on this one.
Rules only fire once each time their condition is true,
provided that the
facts the condition refers to are not modified, i.e. if I only
have one
rule:
(defrule test
(fact)
=>
(printout t "fired!" crlf))
it will only fire once as (fact) is not modified.
I am running Jess from Java. Even when I invoke the rete.run()
method
twice the rule still fires once. I want a behavior in which
the rule fires
once each time I call the run() method. What I mean is that two
consecutive calls to run should produce as output:
fired!
fired!
Resetting the engine (rete.reset()) is not a satisfactory
solution,
because I don't want to reset my working memory also. Neither is
implementing a rule:
(defrule test
?f <- (fact)
=>
(retract ?f)
(printout t "fired!" crlf)
(assert ?f))
as this will result in firing the rule ad infinitum during one
run.
I considered enriching the LHS of all my rules with a special
designated
fact, say (fire-again) and retract and assert it in between
each call to
run, i.e.:
(defrule test
(fire-again)
(fact)
=>
(printout t "fired!" crlf)
)
(reset)
(assert (fire-again))
(run)
(retract-string "(fire-again)")
(assert (fire-again))
(run)
and this seems to get me the behavior I want.
Before I rush to preprocessing all my rules in Java I wondered
if there
are other (better) ways to get the behavior I want?
Kind regards,
Nick.
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Ernest Friedman-Hill
Informatics & Decision Sciences, Sandia National Laboratories
PO Box 969, MS 9012, Livermore, CA 94550
http://www.jessrules.com
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