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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>According to MVEL they’ve added a convenience for
checking the “emptiness” of a value (see: <a
href="http://mvel.codehaus.org/Value+Tests"
title="http://mvel.codehaus.org/Value+Tests">http://mvel.codehaus.org/Value+Tests</a>
)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>In MVEL you’d simply write: myMap == empty<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>This seemed like a MUCH cleaner way to write some of the LHS
of the rules, so I thought I’d try it out. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Given the following rule:<o:p></o:p></span></font></p>
<p class=MsoNormal><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>rule</span></font></b><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'> </span></font><font
size=2 color=green face="Courier New"><span style='font-size:10.0pt;font-family:
"Courier New";color:green'>"Check Empties - Original"</span></font><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
</span></font><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>when <o:p></o:p></span></font></b></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
$grabBag : MyGrabBag(someMap != null)</span></font><font size=2
face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
</span></font><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>eval</span></font></b><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
($grabBag.getSomeMap().size() == 0)</span></font><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
</span></font><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>then<o:p></o:p></span></font></b></p>
<p class=MsoNormal><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>end<o:p></o:p></span></font></b></p>
<p class=MsoNormal><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'><o:p> </o:p></span></font></b></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>This could be rewritten:<o:p></o:p></span></font></p>
<p class=MsoNormal><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'><o:p> </o:p></span></font></b></p>
<p class=MsoNormal><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>rule</span></font></b><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'> </span></font><font
size=2 color=green face="Courier New"><span style='font-size:10.0pt;font-family:
"Courier New";color:green'>"Check Empties - Simple"</span></font><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
</span></font><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>when <o:p></o:p></span></font></b></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'>
MyGrabBag(someMap == </span></font><b><font size=2 color="#960000"
face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New";
color:#960000;font-weight:bold'>empty</span></font></b><font size=2
color=black face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New";
color:black'>)</span></font><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:black'> </span></font><b><font
size=2 color="#960000" face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New";color:#960000;font-weight:bold'>then<o:p></o:p></span></font></b></p>
<p class=MsoNormal><b><font size=2 color="#960000" face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:#960000;font-weight:
bold'>end<o:p></o:p></span></font></b></p>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>The IDE (Eclipse 3.4.2 w/ Drools plugin) seems to recognize
“empty” is a keyword (it makes it bold), but the drools
compiler in the IDE reports:<br>
BuildError: Unable to create restriction '[VariableRestriction: == empty ]' for
field 'someMap' in the rule 'Check Empties - Simple'<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>BuildError: Unable to return Declaration for identifier
'empty'<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Am I assuming incorrectly that the LHS is fully MVEL
compliant?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
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