Hi Alan,
You're not missing anything obvious; your analysis of the problem is
good, and you've figured out for yourself that there's something funny
about how Jess's pseudo-LISP is implemented. In a real LISP, all data
structures are made out of cons cells, and a list we think of as a
function call (like (bind ?x foo)) is no different than one that looks
like a fact (like (initial-fact)). In Jess, though, everything is not
built from cons cells. There are instead Fact and Funcall and Defrule
objects. This is nice and object-oriented, but the problem with this
approach is that the decision to turn a bunch of characters into a
Fact or Funcall or whatever is made when the text is parsed. The
parser therefore has to be built to recognize the language syntax of
rules and facts etc., unlike the LISP reader which is far simpler and
more generic. In any case, this sort of explains why there's no
quote operator: there's no such thing as a generic, uninterpreted list
in Jess.
In any event, Jess 6.0a1 actually has a new function in it that does
more or less what you want. it's called (call-on-engine) and you can
use it as shown below. In this snippet, I create a second Rete
instance from within the main one and store it in variable ?e; I then
assert various facts into it, reset it, call (facts) on it, etc. I
make a local (facts) call too so you can see that the facts are in the
"other" engine, not the one connected to the command line
directly. Let me know what you think.
bash-2.03# java jess.Main
Jess, the Java Expert System Shell
Copyright (C) 1998 E.J. Friedman Hill and the Sandia Corporation
Jess Version 6.0a1 4/25/2000
Jess> (bind ?e (new jess.Rete))
<External-Address:jess.Rete>
Jess> (call-on-engine ?e (assert (foo bar)))
<Fact-0>
Jess> (call-on-engine ?e (facts))
f-0 (foo bar)
For a total of 1 facts.
Jess> (facts)
For a total of 0 facts.
Jess> (deftemplate boo (slot bar))
TRUE
Jess> (call-on-engine ?e (assert (boo (bar 3))))
<Fact-1>
Jess> (call-on-engine ?e (facts))
f-0 (foo bar)
f-1 (boo (bar 3))
For a total of 2 facts.
Jess> (call-on-engine ?e (reset))
TRUE
Jess> (call-on-engine ?e (facts))
f-0 (initial-fact)
For a total of 1 facts.
Jess>
I think Alan Littleford wrote:
> I'm doing some experiments with mutiple engines within the same process and I hit
>the following
> issue. I'd like to construct a function that lets me assert a fact in a different
>engine - i.e. I'd
> like to do something like
>
> (defrule ..
> (some-fact ?parameter)
> (other-engine-instance ?rete)
> =>
> (assert-across-engines ?rete (a-new-fact ?parameter))
> ..)
>
> The way I see it is I can turn my fact into a string:
>
> (assert-across-engines ?rete (str-cat "(a-new-fact " ?parameter ")"))
>
> and use assertString inside my function. sadly this fails if any of the slots are
>Java objects. Or I
> can create a new Fact
> in the new context then munge over the slots, parameter at a time, which at least
>lets me pass Java
> object references. Both techniques are, of coure, slow and messy.
>
> What I want to write is what I wrote - the exact analogue to (assert (a-new-fact
>?parameter)). It
> seems to me that something along the lines of the lisp ' would be useful (I think I
>have this correct
> - it has been an ____age____ since I wrote any lisp) i.e. don't evaluate this, just
>treat it as a
> form: (assert-across-engines ?rete '(a-new-fact ?parameter)).
>
> Or am I missing something _very_obvious here .. ??
>
> Tnx
> Alanl
>
>
>
>
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Ernest Friedman-Hill
Distributed Systems Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
Org. 8920, MS 9012 [EMAIL PROTECTED]
PO Box 969 http://herzberg.ca.sandia.gov
Livermore, CA 94550
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