I don't think there's any way to make the compiler recognize
a character from a string as an ActionScript operator.
I would keep the two numeric parts as variables num1 and
num2, and if the operator can vary, set a variable like op = 1 if
you need an addition, op = 2 if you need a multiplication and then
use a switch statement to send the two variables to the appropriate
line where you already have the operator e.g if op == 1 then
num1+num2, if op == 2 then num1*num2 etc.