Mashup Macro - Add/Subtract/Multiply/Divide

This is a basic mashup macro that let's the user use a mathematical operator (add, subtract, multiply, divide) between a selected field from 2 mashup inputs.  

The example below shows multiply.  Modify the operator in this line for add, subtract, or divide: 'array[count][nodeName] = array[count][lhsVar] * array[count][rhsVar];'.

<macro name="Multiply">

        <input    name="xmldoc" type="document"      />
        <presto-meta name="macrotype">user</presto-meta>

        <input name="lhs" type="string" default=""      />
        <presto-meta name="type" variable="lhs" reference="xmldoc">datapath</presto-meta>
        <presto-meta name="label" variable="lhs">Field 1</presto-meta>

        <input name="rhs" type="string" default=""      />
        <presto-meta name="type" variable="rhs" reference="xmldoc">datapath</presto-meta>
        <presto-meta name="label" variable="rhs">Field 2</presto-meta>

        <input name="nodeName" type="string" default="Result"      />
        <output name="result" type="document"      />

        <variable name="repeatingElement" type="string" default=""      />

        <namespaces>
           <namespace prefix="presto"  uri="java:com.jackbe.jbp.jems.client.EMMLPrestoFunctions"      />
       </namespaces>

        <assign outputvariable="repeatingElement" fromexpr="presto:infergroupXPath($xmldoc)"      />

       <if condition="$repeatingElement != '' ">

           <script type="">
           <![CDATA[
               var array;
               var re = repeatingElement.substring(repeatingElement.lastIndexOf("/*:")+3);
               eval('array = xmldoc..*::' + re);
               var count = 0;
               var lhsVar = lhs.substring(lhs.lastIndexOf("/*:")+3);
               var rhsVar = rhs.substring(rhs.lastIndexOf("/*:")+3);

               for each(var record in array){
                   if(array[count].name().uri){
                     default xml namespace = array[count].name().uri;
                   }
                   array[count][nodeName] = array[count][lhsVar] * array[count][rhsVar];
                   count++;
               }
               result = xmldoc;
           ]]>
        </script> 

           <else>     
               <assign fromvar="xmldoc" outputvariable="result"      />
           </else>
       </if>
</macro>