for( 1 .. 10 ) {
	my $print = make_printer( "dir$_" );
	next if 0.3 > rand;
	for( 1 .. 10 ) {
		next if 0.3 > rand;
		$print->( "file$_" );
	}
}

##</code><code>##

sub make_printer {
	my $hdr = shift;
	my $count;
	return bless sub {
		my $item = shift || do {
			print "\n" if $count;
			return;
		};
		print( ( $count ? "," : "$hdr:") , " ", $item );
		++$count;
	}, 'PRINTER';
	sub PRINTER::DESTROY { shift->() }
}