public static function naturalLanguageJoin(
        array $arr,
        string $last = null,
        string $glue = null
    ) {
        $last_item = array_pop($arr);
        if ($arr) {
            return implode($glue ?? ', ', $arr)
                . ' ' . ($last ?? 'and') . ' '
                . $last_item;
        }
        return $last_item;
    }