[rules-dev] Re: [rules-users] No globals in functions?
Edson Tirelli
tirelli at post.com
Wed Oct 15 13:45:38 EDT 2008
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
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