The first option you posted is correct, this one is wrong. Functions are first-order types, you can just pass then as variables. The moment you add parenthesis, it is assumed to be a function call no longer an access to the variable. Check the lua reference manual to get a more detailed explanation on this.
I'm going to have to do this sometime soon, i want to totally cut xml from my AddOn's, even though it's KINDA easy to use.