How to access other arguments from callback function

Question

I'm using emacs-request to get some json data from the web. Here's an example

(defun test (arg1 arg2)
  (request
   "http://httpbin.org/get"
   :params '(("key" . "value") ("key2" . "value2"))
   :parser 'json-read
   :success (cl-function
             (lambda (&key data &allow-other-keys)
               (message "I sent: %S" (assoc-default 'args data))))))

I'm wondering how the callback functions such as :success can have access to arg1 and arg2?

Answer 1

You can either set the lexical-binding variable to t, allowing the lambda to have access to the outer function's arguments, or wrap the :success function in a lexical-let that binds the outer function's arguments for the lambda:

(defun test (arg1 arg2)
  (request
   "http://httpbin.org/get"
   :params '(("key" . "value") ("key2" . "value2"))
   :parser 'json-read
   :success (lexical-let ((arg1 arg1) (arg2 arg2))
              (cl-function
               (lambda (&key data &allow-other-keys)
                 (message "%s %s sent: %S" arg1 arg2 (assoc-default 'args data)))))))