You don't even need the assignment to $trash in there, as the function might as well be declared void (in C or C++, if you're familiar). What you're concerned about is the side-effect of the subroutine.

I tried to come up with a better way to do that, without the global variable, but I think you've hit on the clearest method with that recursion.

(BTW, there is an account for isotope on this machine, though not under that nickname. Thanks for the kind words.)