Huh? It is a bit out of my expectation, I thought it should be very simple
because of my naiveness. So does the same theory applys to the internal
implementation of Jess' assert function?
Thanks,
Paul
From: "Ernest Friedman-Hill" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: [email protected]
Subject: Re: JESS: how do I write my assert function?
Date: Thu, 22 Mar 2007 12:18:49 -0400
On Mar 22, 2007, at 11:42 AM, Shi Paul wrote:
Hi there,
I'm a novice, so pls forgive me if I ask something stupid. I'd like to
add an user function which is doing exactly the same thing as (assert
(abc(slot1 ?s1)(slot2 ?s2))). The parameter for the fact I got within
that function (vv.get(1)) is an instanceof FuncallValue, how could I turn
that parameter into a Fact or maybe a String, so that I can use
engine.assertFact(xx) or engine.assertString(xx)?
Every set of parentheses in Jess code denotes a function call... except
when they don't. These special cases where they don't are traditionally
(in Lisp) called "special forms." Special forms are handled by the parser
itself. "defrule" is a special form, as are other constructs like
'deftemplate', 'defquery', etc. "assert" is also a special form, because
its arguments are facts, not function calls. In other words, you can't do
what you're asking, because the parser is going to have already decided
your fact, above, is a call to function "abc" with calls to "slot1" and
"slot2" as arguments. Because Jess does extremely late binding, the fact
that these functions don't exist won't be determined until you invoke the
functions by calling Value.resolveValue() or any of the xxxValue()
functions that return a scalar like symbolValue() or intValue(). Strictly,
the only way to do what you want is by modifying the parser itself (the
class jess.Jesp).
But if you're willing to live with the fact that the parser won't
error-check your facts (because it doesn't know they are facts) I can
actually describe a hack that *would* work. The argument to your function
will look like a FuncallValue, and you can call funcallValue () to get a
jess.Funcall. This latter class is a subclass of ValueVector. The first
element in the ValueVector is the name of the function, and the later
elements are the arguments. So what you'd have to do is take the name of
the top-level Funcall, and use that as the "head" of the fact; then
collect all the nested Funcalls; each of their names will actually be a
slot name, and their first (and only) argument will be the slot value.
Given these values, you can build a jess.Fact yourself and assert it.
Gross, huh?
---------------------------------------------------------
Ernest Friedman-Hill
Advanced Software Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://www.jessrules.com
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