If the reason for knowing the name of the input variable is so that you can change the variable, then it is not necessary, you can simply pass the variable by reference :-

lnValue = 0
TestProc( lnValue) && by default, passed by reference
? lnValue && Should print 999

FUNCTION TestProc
LPARAMETERS tnParam1
tnParam1 = 999
RETURN

Regards
Mark.

p.s. Sorry if you already know this.