more along the lines of "either I have one or mayday mayday". That would be the Perl way of my $person = $data_source->get_person($id) or die "No person a

more along the lines of "either I have one or mayday mayday". That would be the Perl way of my $person = $data_source->get_person($id) or die "No person available"; ie, there's code to be executed (to raise the error) in the case that there is no person. The callback structure from the article doesn't allow for this.