[rules-dev] Re: [rules-users] No globals in functions?
James C. Owen
jco at kbsc.com
Wed Oct 15 16:20:26 EDT 2008
Greetings:
Having just joined the developers list, one of the ten commandments
back in the old days of using either Java or C or C++ was to avoid
Global variables at all costs. From what I've been reading the past
couple of days is that there are several global variables distributed
throughout the Drools code, is that correct? I could be way off base
but it did seem that someone was having trouble keeping a global in
focus during function calls to a global Logger. Wouldn't a static
Logger be a better solution?
SDG
jco
Senior Consultant / Architect
KnowledgeBased Systems Corporation
http://www.kbsc.com
Co-founder and Director of The October {Technical} Rules Fest -THE
RuleBased Systems Conference Oct 22-24 Dallas, TX
http://www.OctoberRulesFest.org
"This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man."
Hamlet, Act 1, Scene III
http://www-tech.mit.edu/Shakespeare/hamlet/hamlet.1.3.html
On Oct 15, 2008, at 12:45 PM, Edson Tirelli wrote:
>
> It may be invoked by a consequence, an eval, a predicate, or a
> return value constraint.
>
> If you fix it for the consequence in JavaConsequenceBuilder, the
> others will work the same. You will have to change the java.g
> grammar as I mentioned in my previous e-mail to make it work.
>
> []s
> Edson
>
> 2008/10/14 David Sinclair <dsinclair at chariotsolutions.com>
> Edson,
>
> Changing the builder shouldn't be too much of a problem. If I make
> the changes you suggested, how does the global actually get passed
> to the method? For example if something defined a function like
>
> void function doX(int abc) {
> ...
> global.doY(bcd);
> }
> and I rewrite it to be
>
> void function doX(int abc, GlobalType global) {
> ...
> }
>
> Who is the invoker of the method?
>
> thanks
>
> dave
>
>
>
> On Mon, Oct 13, 2008 at 3:24 PM, Edson Tirelli <tirelli at post.com>
> wrote:
>
> Hi Dave,
>
> Excellent!
> I will try to explain the current situation and one possible
> solution, but you may have better ideas.
>
> Functions in Drools are compiled as simple static methods in a
> generated java class. We use MVEL Templates to generate the code of
> the class and the static method.
>
> Take a look at JavaFunctionBuilder.java class for the code
> generation call and at javaFunction.mvel for the code template.
>
> Now, the problem with globals is that they are scoped to
> sessions, not rulebases, so you can not resolve them until runtime.
> You can not for instance, make them a static reference of the
> generated class and set it at rulebase compilation time.
>
> So, my suggestion would be to:
>
> 1. at compile time, use JavaDialect.analyzeBlock() method to analyze
> and find out what are the globals that are used by the funcion
> method code.
>
> 2. modify the code generation to add parameters to that in the
> method call. So, if "log" is a global and if the function is
> declared like this:
>
> function void someFunction( String param ) {
> // ... code ...
> log.something(...);
> // ... code ...
> }
>
> you detect the use of "log" and add it as a parameter of the
> generated method:
>
> ...
> public static void someFunction( Logger log, String Param ) {
> ...
> }
> ...
>
> This way, at runtime we can inject the parameter into the call.
> You can look at JavaConsequenceBuilder.java and javaInvokers.mvel to
> see how we do kind-of the same thing for consequences.
>
> 3. Now the most interesting part. :) We use an ANTLR grammar for
> parsing Java code blocks. You need to change the parser to rewrite
> any function call the user is doing in his code to inject the log
> parameter transparently. I did the very same thing for modify blocks:
>
> modify( $something ) {
> ...
> }
>
> It is not hard once you get the hang of it. It is a bit of "hand
> work" though. Look at the JavaConsequenceBuilder.fixModifyBlocks()
> for what I did. Also, the ANTLR Java grammar is java.g.
>
> Let me know if you have questions or if you have a better idea,
> and welcome aboard!
>
> Cheers,
> Edson
>
>
>
> 2008/10/13 David Sinclair <dsinclair at chariotsolutions.com>
>
> Hi Edson,
>
> My name is dave sinclair. I started using Drools in early August of
> this year, but have a lot of experience with rules engines. I have
> worked primarily with ArtEntrprise and some with PegaRules. I would
> love to help with this project and thought that this may be the area
> to jump in on.
>
> I have the M2 code, and was reading it over the weekend. Mostly the
> core and some of the compilier. If you want to point me in the right
> direction on the global/functions I'd be happy to have a look.
>
> thanks
>
> dave
>
>
> On Mon, Oct 13, 2008 at 9:59 AM, Bagwell, Allen F
> <afbagwe at sandia.gov> wrote:
> Edson,
>
> Thanks for the tip. I figured I'd need to use a workaround like this.
>
> Unfortunately I'm under a series of tight development and test
> deadlines all the way into early summer. Otherwise, I'd have a look.
> Hopefully someone else out there can assist.
>
> Thanks,
> -A
>
> From: rules-users-bounces at lists.jboss.org [mailto:rules-users-bounces at lists.jboss.org
> ] On Behalf Of Edson Tirelli
> Sent: Friday, October 10, 2008 5:46 AM
> To: Rules Users List
> Subject: Re: [rules-users] No globals in functions?
>
>
> Allen,
>
> There is a technical explanation behind that and we never had the
> time to find a way to overcome this limitation. What you can do,
> although not ideal, is to send the global as a parameter:
>
> funcion void foo( Logger log, String cond )
> {
> ...
> }
>
> rule XYZ
> when
> then
> foo( log, someString );
> end
>
> If you or anyone would like to help improving this, let us know
> and we can discuss ways into doing it.
>
> []s
> Edson
>
> 2008/10/9 Bagwell, Allen F <afbagwe at sandia.gov>
>
> There's probably an easy explanation for this. I was wondering about
> why functions inside of rule files can't access globals?
>
> For example, I have a log4j logger that I pass into my rule files
> via a global. The logger should never be a part of working memory.
> It's just there to capture valuable feedback.
>
> But I can't do this:
>
> global Logger log;
>
> function void foo(String cond)
> {
> if (cond == "error")
> log.error("I saw an error");
> }
>
> Because the compiler says that in the function it can't resolve 'log'.
>
> -A
>
> Allen F. Bagwell
> e-mail: afbagwe at sandia.gov
> phone: 505/284-4517
> fax: 505/ 844-7886
>
> There is no monument dedicated to the memory of a committee. --
> Lester J. Pourciau
>
>
>
>
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
>
>
>
> --
> Edson Tirelli
> JBoss Drools Core Development
> JBoss, a division of Red Hat @ www.jboss.com
>
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
>
>
>
>
> --
> Edson Tirelli
> JBoss Drools Core Development
> JBoss, a division of Red Hat @ www.jboss.com
>
>
>
>
> --
> Edson Tirelli
> JBoss Drools Core Development
> JBoss, a division of Red Hat @ www.jboss.com
> _______________________________________________
> rules-dev mailing list
> rules-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-dev
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.jboss.org/pipermail/rules-dev/attachments/20081015/c04ef9ed/attachment.html
More information about the rules-dev
mailing list