our $DEBUG_LEVEL = 5;

sub __dbg (&;$) {
    my ($code, $verbosity) = @_;
    if ($DEBUG_LEVEL >= ($verbosity // 1)) {
        my $msg = join('', $code->());
        print STDERR "DEBUG: ", $msg, "\n" if length($msg);
    }
}

# ...the meat of the package is below...