XPath eval function

Question

I am looking for a function in xPath that is equivalent to eval() in javascript.
Basically I have to fields in  a database used for conversion
Operator --values can be   *   +    -      /
Amount  --numeric value
I want to apply the operator and amount to a value inside a transaction. 
Example. 
Local.Operator =  " * "
Local.Amount = 10
I am looping through tag values and want to dynamically apply the operator and amoun
Local.NewAmount = LoopValue Local.Operator  Local.Amount
I want it to   evaluate it to    Local.NewAmount =   LoopValue * 10 
in javascript it is eval(LoopValue Local.Operator  Local.Amount).
Any ideas how to do this in a transaction?
Thanks

Answer 1

Thanks for the idea, I will give it a try.  
I also created a small transaction that just uses a switch statement based on the operator, and then adds, multiplies etc. Then returns the value.   It works well for reuse, since multiple transactions need this funcitonality.
Just have to see which method works better.
Thanks again,
Jeff