my (%seen, @bad_link);
for my $url (@base_pages) {
    my @work = get_links($url);
    while (@work) {
        my $link = pop @work;
        next if $seen{$link}++;
        if (is_good($link)) {
            push @work, get_links($link);
        }
        else {
            push @bad_link, $link;
        }        
    }
}