let 绑定中的“必需参数不是符号”错误

Question

在下面的代码中，我收到一个Required argument is not a symbol错误。

(defconstant +localhost+ (vector 127 0 0 1))

(defun ip-from-hostname (hostname)
  (sb-bsd-sockets:host-ent-addresses
  (sb-bsd-sockets:get-host-by-name hostname)))

(defun test-connect
    (let ((ip (car (ip-from-hostname "www.google.com")))
              (socket (make-instance 'sb-bsd-sockets:inet-socket :type :stream :protocol :tcp)))
      (sb-bsd-sockets:socket-bind socket +localhost+ 8080)
      (sb-bsd-sockets:socket-connect socket ip)
      (sb-bsd-sockets:socket-send socket "GET / HTTP/1.1" nil)
      (write-line (sb-bsd-sockets:socket-receive socket nil 2048))))

(test-connect)

更完整的错误信息：

Required argument is not a symbol: ((IP
                                       (CAR
                                        (IP-FROM-HOSTNAME "www.google.com")))
                                      (SOCKET
                                       (MAKE-INSTANCE
                                        'SB-BSD-SOCKETS:INET-SOCKET :TYPE
                                        :STREAM :PROTOCOL :TCP)))

我已经将问题缩小到调用部分ip-from-hostname，但奇怪的是在 REPL 中 let 绑定的简化版本：

(let ((ip (sb-bsd-sockets:host-ent-addresses (sb-bsd-sockets:get-host-by-name "www.google.com"))))
  (write-line (write-to-string (car ip))))

我还尝试用ip-from-hostname它的主体替换调用，认为它可能与参数有关，但仍然没有运气。有什么想法吗？

Answer 1

(defun test-connect ...

... 应该是一个缺少的 lambda 列表。

请记住，DEFUN 的语法是：

defun function-name lambda-list
  [[declaration* | documentation]]
  form*