sub process_files ($ext, @files) {
	# let's say we split @files in two sets
	my @foo_files = ...;
	my @bar_files = ...;
	# but part of the processing is the same
	my $new_name = sub ($name, $some_param) {
		... # some longer/complex code to munge the filename
		# note how this uses at least one var from the outer scope
		return $new_filename . $ext;
	};
	# different processing for the two sets
	for my $file (@foo_files) {
		my $fn = $new_name->($file, "foo");
		...
	}
	for my $file (@bar_files) {
		my $fn = $new_name->($file, "bar");
		...
	}
}