I think Ben Allen wrote:
> I was wondering whether it is possible to create rules from within rules?
Yes, absolutely. Jess is designed as a dynamic system where it's easy
to add and remove rules as the engine runs.
The added rules have to be built up as data (i.e., as a string, as
source code) and handed to the engine to compile and integrate into
the Rete network using the "build" function. It could look like this
interactive session, where a new rule is defined to match a "foo" fact
containing a single constant value. The value is pulled out of a "data"
fact, and used to build a new rule. Note that the ?X is the *only* part
of the new rule that's not in double quotes -- we're taking the value
of the variable ?X at one point in time, and hard-coding it into a new
rule. Remember that Jess strings can contain newlines.
----------------------------------------------------------------------
Jess> (defrule make-new-rule
(data ?X)
=>
(build
(str-cat "(defrule new-rule
(foo " ?X ")
=>
(printout t \"Found matching foo fact.\" crlf))")))
TRUE
Jess>
(reset)
TRUE
Jess> (watch all)
TRUE
Jess> (assert (data 1))
==> f-1 (MAIN::data 1)
==> Activation: MAIN::make-new-rule : f-1
<Fact-1>
Jess> (run)
FIRE 1 MAIN::make-new-rule f-1
MAIN::new-rule: +1+1+1+1+t
<== Focus MAIN
1
Jess> (ppdefrule new-rule)
"(defrule MAIN::new-rule
(MAIN::foo 1)
=>
(printout t \"Found matching foo fact.\" crlf))"
Jess>
So you see, Alan was right. There is a super-simple way to do it. :)
---------------------------------------------------------
Ernest Friedman-Hill
Science and Engineering PSEs Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://herzberg.ca.sandia.gov
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