in reply to How do you tell if a sub argument is an lvalue?
Also look at Want, which answers the general question, rather than just to test for readonliness.
Oh Lord, won’t you burn me a Knoppix CD ?
My friends all rate Windows, I must disagree.
Your powers of persuasion will set them all free,
So oh Lord, won’t you burn me a Knoppix CD ?
(Missquoting Janis Joplin)