PHP -- using an anonymous function while concatenating : Does PHP allow an anonymous function during concatenating?

If so, what is the proper syntax?

Here's an example I can't get to work:

    $final_text = $some_initial_string
        . function ($array_of_strings) {
                $out = '';
                foreach($array_of_strings as $this_particular_string) {
                    $out .= $this_particular_string;
                }
                return $out_string;
            };