Getopt.pm

our sub MAIN_HELPER($retval = 0) is export {
    say "doing getopty stuff!";
    my $m = callframe(1).my<&MAIN>;
    return $retval unless $m;
    say 'calling MAIN with no args';
    $m();
}

test.pl

use v6;
use Getopt;

sub MAIN() {
    say 'The rain in MAIN falls mainly on the plain';
}