Iterator Operations

If the iterator returns the list items in some canonical order, you can do this:

        my $both = both($it1, $it2);
        $item = $both->();   # get next item from $it1 or $it2

        # Get rest of items in appropriate order
        while (defined($item = $both->())) {
          #...
        }

The both function works for any iterators
If an iterator represents a database query, this is the OR operation
- Straightforward implementation on next slide
- AND is a little harder, but not much