Using this[]to reference a variable - not working!

I’m writing a function which can take the names of different variables and use them to do some calculations. Long story short, I want to be able to call the function like this:

function caseConditionEvaluator( nameOfVariable:String )

It probably seems like a really roundabout way to pass the variable through its name rather than just passing the variable itself. This is related to me using XML to get the variable names, so they come in as strings. Just bear with me here.

Inside the function, I want to be able to do something like this:

trace( this[nameOfVariable] )

which should then trace the variable’s value. Unfortunately, I just get an ‘undefined’. How do I use ‘this[]’ to get the value of the variable from a string corresponding to the variable’s name?