public function prompt($question, $default = null, $marker = ': ')
    {
        if (isset($default) && strpos($question, '[') === false) {
            $question .= ' [default: ' . $default . ']';
        }

        $this->out($question . $marker);

        $input = $this->in();

        if ($input === '') {
            return $default;
        }

        return $input;
    }