/**
     * 中间件调度
     * @access public
     * @param  Request  $request
     * @param  string   $type  中间件类型
     */
    public function dispatch(Request $request, $type = 'route')
    {
        return call_user_func($this->resolve($type), $request);
    }

protected function resolve($type = 'route')
    {
        return function (Request $request) use ($type) {

            $middleware = array_shift($this->queue[$type]);

            if (null === $middleware) {
                throw new InvalidArgumentException('The queue was exhausted, with no response returned');
            }

            list($call, $param) = $middleware;

            try {
                $response = call_user_func_array($call, [$request, $this->resolve($type), $param]);
            } catch (HttpResponseException $exception) {
                $response = $exception->getResponse();
            }

            if (!$response instanceof Response) {
                throw new LogicException('The middleware must return Response instance');
            }

            return $response;
        };
    }

重点讲解一下resolve方法，有个递归好想，没看懂