You might want to take a look at How To: Make An Iterator which I expanded a bit further for a perl.com article here. If you want to take it even further, you should take a look at Higher Order Perl by Dominus you are shown how to treat the iterator as a list for the purposes of filtering and transforming.

It is not too uncommon to have an iterator to an infinite list - what then should be the behavior if you ask for the entire list? I think a more sane approach would be to provide a parameter to ask for a specific number of fetches. Remember that $next->() doesn't always have to have an empty argument list. You could even have an optional start position so that you can fetch the next 10 values or the first 10. The amount of extensibility is really just restricted by the size of the memory footprint you are willing to let the iterator have.