Indeed, it's not legal for a Userfunction to return null. You should
return Funcall.NIL if your function returns no value. I will put this
in the manual, because it doesn't seem to say this anywhere. Thanks
for writing.
I think =?US-ASCII?Q?Emmanuel_Lecharny?= wrote:
> My code is throwing an exception in the If.java class.
>
> The reason is : the updateDB-my-fact returns null, which is not allowed in
> the "if" function.
>
> As "if" is a function, it searchs for the "else" function in its parameters.
> Of couse, as my function returns null, Jess can't compare it with "else", so
> I obtain an exception.
>
> Of course, my function could have returned a Value, but as far as it just
> set a flag, it didn't. And it works well in the RHS part of other rules, so
> this is a special case.
>
> Guideline : a user-defined function MUST return a Value in order to be used
> in a "if" expression.
>
> Emmanuel Lecharny, IKTEK
> 06 08 33 32 61, www.iktek.com <http://www.iktek.com>
>
>
> -----Message d'origine-----
> De : [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]De
> la part de [EMAIL PROTECTED]
> Envoye : vendredi 11 mai 2001 13:24
> A : =?iso-8859-1?Q?Emmanuel_L=E9charny?=
> Cc : [EMAIL PROTECTED]
> Objet : Re: JESS: Problem with "if" and multiple expressions with user
> function call
>
>
> The exception message "Error during execution" is what the
> Funcall.execute() method says when a called Java function throws an
> exception. In this case, the stack trace you get from catching the
> JessException and printing it out isn't necessarily the most
> informative one -- you want the exception object thrown by the Java
> method. That exception, thrown by your Java function, would most
> likely tell you what the problem is. So, when you write Java code to
> work with Jess, you should handle JessExceptions something like this:
>
>
> } catch (JessException re) {
> if (re.getNextException() != null) {
> System.out.println(re.toString());
> System.out.print("\nNested exception is:\n");
>
> System.out.print.println(re.getNextException().getMessage());
> re.getNextException().printStackTrace(System.out);
>
> } else
> re.printStackTrace(m_rete.getErrStream());
>
> If you make these changes, you'll probably find out right away what is
> going wrong.
>
>
>
> I think =?iso-8859-1?Q?Emmanuel_L=E9charny?= wrote:
> [Charset iso-8859-1 unsupported, filtering to ASCII...]
> > Hi,
> >
> > I have a problem when I use a multiple expression, in which I call a user
> > function in a if-then-else statement :
> >
> > ... (rule)
> > ?my-fact <- (STUFF (value ?value))
> > (CONTROL (current-value ?cv) (maximum ?max))
> > =>
> > (bind ?new-value (+ ?cv ?value)
> > (if (>= ?new-value ?max)
> > then
> > (modify ?my-fact (state 4) (value ?new-value))
> > (updateDB-my-fact ?my-fact-id 4 ?new-value)
> > else
> > (modify ?my-fact (state 2) (value ?new-value))
> > (updateDB-my-fact ?my-fact-id 2 ?new-value)
> > )
> >
> > This is what I get (I don't know if I deserve it ;) :
> >
> > Jess reported an error in routine Funcall.execute
> > while executing (if (>= ?new-value ?max) then (modify-n ?my-fact
> > <External-Address:[I> 4 <External-Address:[I> ?new-value)
> > (updateDB-my-fact ?my-fact-id 4 ?new-value) else (modify-n ?my-fact
> > <External-Address:[I> 2 <External-Address:[I>
> > ?new-value) (updateDB-my-fact ?my-fact-id 2 ?new-value))
> > while executing defrule my-rule.
> > Message: Error during execution.
> > at java.lang.Throwable.<init>(Throwable.java:84)
> > at java.lang.Exception.<init>(Exception.java:35)
> > at jess.JessException.<init>(JessException.java:53)
> > at jess.Funcall.execute(Funcall.java:254)
> > at jess.Defrule.fire(Defrule.java:205)
> > at jess.Activation.fire(Activation.java:65)
> > at jess.Agenda.run(Agenda.java:126)
> > at jess.Agenda.run(Agenda.java:102)
> > at jess.Rete.run(Rete.java:752)
> > at com.Motor.treatMyStuff(Moteur.java:340)
> > at java.lang.reflect.Method.invoke(Native Method)
> > at
> > sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:242)
> > at sun.rmi.transport.Transport$1.run(Transport.java:155)
> > at java.security.AccessController.doPrivileged(Native Method)
> > at sun.rmi.transport.Transport.serviceCall(Transport.java:152)
> > at
> > sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:462)
> > at
> >
> sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:6
> > 62)
> > at java.lang.Thread.run(Thread.java:498)
> >
> > updateDB-my-fact is a Java function, which work perfectly well if I call
> it
> > outside the then or else part. A workaround I found is something like :
> >
> > ...
> > (if (>= ?new-value ?max)
> > then
> > (modify ?my-fact (state 4) (value ?new-value))
> > (bind ?new-state 4)
> > else
> > (modify ?my-fact (state 2) (value ?new-value))
> > (bind ?new-state 2)
> > )
> >
> > (updateDB-my-fact ?my-fact-id ?new-state ?new-value)
> > ...
> >
> > which works well.
> >
> > Emmanuel L_charny, IKTEK
> > 06 08 33 32 61, www.iktek.com
> >
>
>
>
> ---------------------------------------------------------
> 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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---------------------------------------------------------
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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