[rules-users] Newbie question on accessing predecessor and successor in a list

[CSchr]

Thanks Greg for your fast reply. Unfortunately I do not get this to work:

$preSegment : Segment ( 
                       $journey.segmentList.indexOf(this) ==
($journey.segmentList.indexOf($segment) - 1), 
                       countries not contains Country.Switzerland && ...
 		     ) from $journey.segmentList

Compiler throws:

[36,48]: unknown:36:48 Unexpected token 'this'[36,98]: unknown:36:98
Unexpected token '$segment'

Is it possible to use eval() inside Segment ()? 

With eval the compiler throws something like this:

$journey.segmentList cannot be resolved to a type
Cannot use this in a static context

I don't know how matching works in drools, but wouldn't this also be very
expensive? As for every match of Segment ( ) the segmentList has to be
iterated two times. These lists can get very long. A cheap approach would be
if the from statement would "know" the index of the Segment () matched. I
was hoping this would be possible.


Regards,

Chris


Greg Barton wrote:
> 
> You can't do $journey.segmentList.indexOf(this) and
> $journey.segmentList.indexOf($segment), even in an eval?
> 
> --- On Mon, 11/3/08, CSchr <christian.schrinner at sbb.ch> wrote:
> 
>> From: CSchr <christian.schrinner at sbb.ch>
>> Subject: [rules-users] Newbie question on accessing predecessor and
>> successor in a list
>> To: rules-users at lists.jboss.org
>> Date: Monday, November 3, 2008, 9:56 AM
>> Hi everyone!
>> 
>> I'm relatively new to Drools and rule languages.
>> 
>> I'm wondering if it is possible to access the
>> predecessor and successor in a
>> match using from operator on an (Array)List. I have
>> something like this
>> (simplified):
>> 
>> ...
>> $segment : Segment( countries contains Country.Switzerland
>> && ... ) from
>> $journey.segmentList
>> 
>> $preSegment : Segment ( indexOf(this) == indexOf($segment)
>> - 1, 
>> 			           countries not contains Country.Switzerland
>> && ...
>> 		    ) from $journey.segmentList
>> 
>> I need something like indexOf() for the exact predecessor
>> of the matched
>> segment.
>> 
>> If the matched business object was an element of a double
>> linked list it
>> would be easy. Unfortunately I don't have the luxury to
>> change the business
>> object into knowing it's predecessor or successor. I
>> have to prove that we
>> could write our java coded business rules in Drools rule
>> language without
>> changing the business object model.
>> 
>> Thanks in advance,
>> 
>> Chris
>> 
>> 
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>> Nabble.com.
>> 
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> 
> 
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