In an $Included TeamScript, can I tell if something's already defined?

Question posted 7/31/08 by a zonderman

I have a script that I use $Include() to insert into other scripts. The included script defines a few functions and Constants. I would like the $Included script to be able to check if any of those constants/functions are already defined (ie from the wrapper-script). If so, it would not define them a second time.
Basically, I think I would like something like the #IFDEF pre-processor directive. Is there anything like this for TeamScript/VBS?
Thanks in advance.
Ariela Z