public function getCallbackCode()
    {
        $reflection = new \ReflectionFunction($this->_callback);
        
        // Open file and seek to the first line of the closure
        $file = new \SplFileObject($reflection->getFileName());
        $file->seek($reflection->getStartLine() - 1);

        // Retrieve all of the lines that contain code for the closure
        $code = '';
        while ($file->key() < $reflection->getEndLine())
        {
            $code .= $file->current();
            $file->next();
        }

        $begin = strpos($code, 'function');
        $end = strrpos($code, '}');
        $code = substr($code, $begin, $end - $begin + 1);

        return $code;
    }