# With the above library, we can write our worker code without
    # having to specifiy whether we are interested in matching (=~)
    # or non-matching (!~).  Instead, we can parameterize this
    # behavior by allowing our worker to accept a matcher as an
    # argument:

    my @candidates = map {chomp;$_} <DATA>;

    sub do_work {
        my $matcher = shift;
        foreach (@candidates) {
            if ($matcher->($_)) {  # instead of regex op
                # do something with candidate in $_
                print "$_$/";
            }
        }
    }