See Higher Order Perl, Chapter 4.5 THE SEMIPREDICATE PROBLEM 
# array reference version
sub make_iterator {
    ... return Iterator {
        my $return_value;
        ...
          if (exhausted)
        {
            return;
        }
        else {
            return [$return_value];
        }
    }
}

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In reply to Re: Dumb, non-question: How to return 'nothing'. by Anonymous Monk
in thread Dumb, non-question: How to return 'nothing'. by BrowserUk

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