Understood. I've got it working according to your hack. 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 13:10:52 -0400
On Mar 22, 2007, at 12:33 PM, Shi Paul wrote:
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?
Imagine saying "I'd like to write a new Java keyword 'foo' which is the
same as 'class' but a little different. 'foo' should be followed by a
class definition." Silly, right? It's pretty obvious it can't be done
without modifying the Java compiler.
What you're asking is the equivalent thing in Jess. "assert" is special
just like "class" is special; the Jess compiler knows about "assert" just
like the Java compiler knows about "class". You can't write a function in
Jess that behaves like 'assert' anymore than you can write a function in
Java which behaves like 'class'.
Now, as it happens, there is an ugly hack which will let you do what you
want in Jess, and I described it below. But it is just a hack, not
something I'd expect anyone to do in production code. If you really want
to extend the Jess language in this way, then you need to modify the
parser itself.
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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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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