Re: Error with add-function and process-filter

[tpeplt <tpeplt@gmail.com>]

hendeigr via Users list for the GNU Emacs text editor
<help-gnu-emacs@gnu.org> writes:

> Hi -
>
> (Apologies if this is a dup - my first attempt seemed to disappear so
> after 24 hours, I have resent).
>
> I'm new to elisp and am trying to use add-function/remove-function to
> add/remove a custom process filter (in order to automate some commands
> in vterm). I thought I followed the example here:
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Advising-Functions.html
> 
> defun h/trace (proc string)
>  (message (format "tracing: %s" string)))
> 
> defun h/test ()
>  (interactive)
>  (set-buffer (vterm))
>  (let* ((h-proc (get-buffer-process (current-buffer))))
>    (message (format "%s" (process-filter h-proc)))
>    (add-function :before (process-filter h-proc) #'h/trace)
>    (term-send-raw-string "ssh whatami@doingwrong.here")
>    (remove-function (process-filter h-proc) #'h/trace)))

1. When you are editing an Emacs Lisp file, then two details for you to
   note are that a) the major mode is Emacs Lisp (indicated by the text
   (Elisp... in the mode line) and b) the menu bar will include an
   "Emacs-Lisp" entry.  While you are new to Emacs Lisp, it will be
   helpful for you to use that menu item.  (If you spend a lot of time
   writing in Emacs Lisp, then you will eventually want to learn key
   sequences and command names that will enable you to execute commands
   more quickly.)

   Using the "Emacs-Lisp" menu, locate the "Byte-compile This File"
   entry.  When you click on this, then for the code that you provided, you
   will see the following warnings:

   In h/trace:
      Warning: Unused lexical argument `proc'

   In end of data:
     Warning: the function ‘term-send-raw-string’ is not known to be defined.
     Warning: the function ‘vterm’ is not known to be defined.

   (File name and line/columns numbers omitted.)  These warning messages
   may vary depending on your version of Emacs.

2. In addition to the byte-compiler, Emacs includes a lint utility that
   can be helpful for finding errors (although it can have problems
   understanding macros, but that mostly should not be a concern for new
   users).  To run the Emacs lint on your buffer’s contents follow the menu
   from Emacs-Lisp -> Linting -> Lint Buffer.

Once you have resolved any byte-compiler problems, then if your problem
still persists you should send a sufficiently complete segment of code
that allows readers to byte-compile the code and reproduce the problem.

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