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<TITLE>IRC: interesting topic: use of lists using "from" in LHS and iterated over in RHS</TITLE>
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<P><FONT SIZE=2 FACE="Arial">HI,</FONT>
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<P><FONT SIZE=2 FACE="Arial">There was an interesting discussion today on IRC; a user "jochen" reported NPEs when trying to iterate lists in the RHS constructed in the LHS using "from collect".</FONT></P>
<P><FONT SIZE=2 FACE="Arial">I was wondering how Drools handles lists constructed in the LHS; if the list contained 5 elements but another rule retracted one of those elements would the list available in the RHS contain 4 or 5 elements?</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Here's a simplification of what was posted at </FONT><A HREF="http://pastebin.com/yKGSxFkA"><U><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">http://pastebin.com/yKGSxFkA</FONT></U></A>
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<P><FONT SIZE=2 FACE="Arial">Rule 1</FONT>
<BR><FONT SIZE=2 FACE="Arial">when</FONT>
<BR> <FONT SIZE=2 FACE="Arial">$cheese : ArrayList() from collect(CheeseFact());</FONT>
<BR><FONT SIZE=2 FACE="Arial">then</FONT>
<BR> <FONT SIZE=2 FACE="Arial">for(int i=0; i<$cheese.size(); i++) {</FONT>
<BR> <FONT SIZE=2 FACE="Arial">//Something useful…</FONT>
<BR> <FONT SIZE=2 FACE="Arial">}</FONT>
<BR><FONT SIZE=2 FACE="Arial">end</FONT>
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<P><FONT SIZE=2 FACE="Arial">What if there was another rule that did something like this:-</FONT>
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<P><FONT SIZE=2 FACE="Arial">Rule 2</FONT>
<BR><FONT SIZE=2 FACE="Arial">When </FONT>
<BR> <FONT SIZE=2 FACE="Arial">$cf : CheeseFact(type == "chedder")</FONT>
<BR><FONT SIZE=2 FACE="Arial">Then</FONT>
<BR> <FONT SIZE=2 FACE="Arial">retract($cf);</FONT>
<BR><FONT SIZE=2 FACE="Arial">end</FONT>
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<P><FONT SIZE=2 FACE="Arial">What would be the list Rule 1 iterates?</FONT>
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<P><FONT SIZE=2 FACE="Arial">I'd assume since I believe activation execution to be serial it would depend on the agenda's conflict resolution strategy or rule salience?</FONT></P>
<P><FONT SIZE=2 FACE="Arial">What would be the learned opinion?</FONT>
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<P><FONT COLOR="#000000" SIZE=2 FACE="Arial">With kind regards,</FONT>
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<P><FONT COLOR="#000000" SIZE=2 FACE="Arial">Mike</FONT>
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