Join strings recursively

I didn’t want to search for it, so I made mine:

• python:

def join(l):
    """ Joins pieces with a connector recursively """
    if type(l) is list:
        if len(l) < 3:
            exit("ERROR: there aren't any pieces to join")
        c0 = join(l[0])
        c2 = join(l[2:]) if len(l) > 3 else join(l[2])
        if all([c0,c2]):
            return "%s%s%s" % (c0, l[1], c2)
        else:
            return c0 or c2
    else:
        return l

• php:

/**
 * Function to construct a "clean" text by passing
 * an array of words and its connectors.
 */
function join_clean($words){
    if(is_array($words)){
        if(count($words) < 3)
            die("ERROR: there aren't any pieces to join");
        $c0 = join_clean($words[0]);
        if(count($words) > 3)
            $c2 = join_clean(array_slice($words, 2));
        else
            $c2 = join_clean($words[2]);
        if($c0 && $c2)
            return $c0.$words[1].$c2;
        elseif($c0)
            return $c0;
        else
            return $c2;
    }else
        return $words;
}