通过cl-function传递回调

Question

我正在尝试使用来自REST API 的出色request.el库请求数据：

(request
 "http://httpbin.org/get"
 :params '(("key" . "value") ("key2" . "value2"))
 :parser 'json-read
 :success (function*
           (lambda (&key data &allow-other-keys)
             (message "I sent: %S" (assoc-default 'args data)))))

哪个很好。作为一个新手，我真的不知道在function*这里做什么，我只是从request.el-examples 那里得到的。

然后，我尝试将此调用包装到一个函数中以减少样板，如下所示：

(defun my/do-request (callback)
  (request
   "http://httpbin.org/get"
   :params '(("key" . "value") ("key2" . "value2"))
   :parser 'json-read
   :success callback))

(my/do-request (lambda (data)
                 (message "got data: %s" data)))

但是回调没有被调用吗？我也尝试过像这样传递回调：

(defun my/do-request (callback)
  (request
   "http://httpbin.org/get"
   :params '(("key" . "value") ("key2" . "value2"))
   :parser 'json-read
   :success (function*
             (lambda (&key data &allow-other-keys)
               (callback data)))))

结果相同。我以为这里可能需要词法绑定，但这也无济于事。

如何在此处减少样板代码？

Answer 1

调用新函数时，通常最好使用与原始值完全相同的值来尝试它：

(my/do-request
 (function*
  (lambda (&key data &allow-other-keys)
   (message "I sent: %S" (assoc-default 'args data)))))

上面打印了所需的消息。

第一种方法

您按如下所示调用了代码，但未打印任何内容：

(my/do-request (lambda (data)
                 (message "got data: %s" data)))

原来有一个错误，但不幸的是它没有到​​达用户。如有疑问，应启用调试器：

(setf debug-on-error t)

*scratch*完成M-:（eval-expression）之后，您可以在缓冲区或迷你缓冲区中评估上述内容。

然后，当您重新评估呼叫时，应显示以下内容：

Debugger entered--Lisp error: (wrong-number-of-arguments (lambda (data) (message "got data: %s" data)) 8)
  (lambda (data) (message "got data: %s" data))(:data ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . .....) (url . "http://httpbin.org/get?key=value&key2=value2")) :symbol-status success :error-thrown nil :response [cl-struct-request-response 200 nil ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . .....) (url . "http://httpbin.org/get?key=value&key2=value2")) nil success "http://httpbin.org/get?key=value&key2=value2" nil (:params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response #0) #<killed buffer> "HTTP/1.1 200 OK\nConnection: keep-alive\nServer: gunicorn/19.8.1\nDate: Thu, 05 Jul 2018 11:44:15 GMT\nContent-Type: application/json\nContent-Length: 249\nAccess-Control-Allow-Origin: *\nAccess-Control-Allow-Credentials: true\nVia: 1.1 vegur\n" nil curl nil])
  apply((lambda (data) (message "got data: %s" data)) (:data ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) :symbol-status success :error-thrown nil :response [cl-struct-request-response 200 nil ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) nil success "http://httpbin.org/get?key=value&key2=value2" nil (:params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response #1) #<killed buffer> "HTTP/1.1 200 OK\nConnection: keep-alive\nServer: gunicorn/19.8.1\nDate: Thu, 05 Jul 2018 11:44:15 GMT\nContent-Type: application/json\nContent-Length: 249\nAccess-Control-Allow-Origin: *\nAccess-Control-Allow-Credentials: true\nVia: 1.1 vegur\n" nil curl nil]))
  apply(apply (lambda (data) (message "got data: %s" data)) (:data ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) :symbol-status success :error-thrown nil :response [cl-struct-request-response 200 nil ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) nil success "http://httpbin.org/get?key=value&key2=value2" nil (:params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response #1) #<killed buffer> "HTTP/1.1 200 OK\nConnection: keep-alive\nServer: gunicorn/19.8.1\nDate: Thu, 05 Jul 2018 11:44:15 GMT\nContent-Type: application/json\nContent-Length: 249\nAccess-Control-Allow-Origin: *\nAccess-Control-Allow-Credentials: true\nVia: 1.1 vegur\n" nil curl nil]))
  request--safe-apply((lambda (data) (message "got data: %s" data)) (:data ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) :symbol-status success :error-thrown nil :response [cl-struct-request-response 200 nil ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) nil success "http://httpbin.org/get?key=value&key2=value2" nil (:params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response #1) #<killed buffer> "HTTP/1.1 200 OK\nConnection: keep-alive\nServer: gunicorn/19.8.1\nDate: Thu, 05 Jul 2018 11:44:15 GMT\nContent-Type: application/json\nContent-Length: 249\nAccess-Control-Allow-Origin: *\nAccess-Control-Allow-Credentials: true\nVia: 1.1 vegur\n" nil curl nil]))
  request--callback(#<killed buffer> :params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response [cl-struct-request-response 200 nil ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) nil success "http://httpbin.org/get?key=value&key2=value2" nil (:params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response #0) #<killed buffer> "HTTP/1.1 200 OK\nConnection: keep-alive\nServer: gunicorn/19.8.1\nDate: Thu, 05 Jul 2018 11:44:15 GMT\nContent-Type: application/json\nContent-Length: 249\nAccess-Control-Allow-Origin: *\nAccess-Control-Allow-Credentials: true\nVia: 1.1 vegur\n" nil curl nil])
  apply(request--callback #<killed buffer> (:params (("key" . "value") ("key2" . "value2")) :parser json-read :success (lambda (data) (message "got data: %s" data)) :error #[128 "\302\300\303\301\"\"\207" [request-default-error-callback ("http://httpbin.org/get") apply append] 6 "\n\n(fn &rest ARGS2)"] :url "http://httpbin.org/get?key=value&key2=value2" :response [cl-struct-request-response 200 nil ((args (key . "value") (key2 . "value2")) (headers (Accept . "*/*") (Accept-Encoding . "deflate, gzip") (Connection . "close") (Host . "httpbin.org") (User-Agent . "curl/7.55.1")) (origin . ...) (url . "http://httpbin.org/get?key=value&key2=value2")) nil success "http://httpbin.org/get?key=value&key2=value2" nil #0 #<killed buffer> "HTTP/1.1 200 OK\nConnection: keep-alive\nServer: gunicorn/19.8.1\nDate: Thu, 05 Jul 2018 11:44:15 GMT\nContent-Type: application/json\nContent-Length: 249\nAccess-Control-Allow-Origin: *\nAccess-Control-Allow-Credentials: true\nVia: 1.1 vegur\n" nil curl nil]))
  request--curl-callback(#<process request curl> "finished\n")

根据文档，回调函数应该是可变参数的，这意味着以下工作：

(lambda (&rest args) (message "got data: %s" args))

但随后，您将看到太多数据。

参数作为键/值对传递。为了获得与:data符号关联的数据，您必须执行以下操作：

(lambda (&rest args)
  (message "got data: %s" (getf args :data)))

结果值是一个关联列表，您可以'args像上面那样（例如(assoc-default 'args data)）从中访问条目。

但是，除了这样做(getf args :data)，您还可以编写：

(lambda (&key data) ...)

特殊&key符号用于自动访问:data隐式参数列表中与之关联的值。但是，关键字参数来自Common Lisp，Emacs Lisp不知道如何立即使用&key。这就是为什么有一个(function* ...)宏环绕lambda的原因。然后，您可以选择使用function*宏或自己处理参数列表，如上所示。这取决于您的需求。根据文档的建议，如果使用&key，也应该使用&allow-other-keys。

第二种方法

在第二种方法中，debug-on-entry设置为t表示这callback不是已知函数：

Debugger entered--Lisp error: (void-function callback)

这是由于Emacs Lisp是Lisp-2，即您不能仅通过将自变量指定为函数调用的第一个元素来调用该函数。Emacs Lisp将语法理解为“调用名为回调的函数”，而不是“调用绑定到变量callback的函数对象”。您需要使用funcall：

(function*
  (lambda (&key data &allow-other-keys)
    (funcall callback data)))

但是使用上面的方法，现在的错误是那callback是一个未定义的变量。而现在，这是由于动态作用域。如果评估以下行并重新评估defun，则代码将按预期工作：

(setf lexical-binding t)

或者，您可以将以下内容作为文件的第一行：

;; -*- lexical-binding: t -*-