[QUESTION] How to use :filter in `make-process'?

[QUESTION] How to use :filter in `make-process'?

[stardiviner]

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I have an code example try to use :filter handler of make-process.

```
(let ((op-fn (lambda () (message "call the fn"))))
  (make-process
   :name "sleep command test"
   :command (list "sleep" "3")
   :filter `(lambda (proc event)
              (message "event catched!")
              (funcall ,op-fn))
   :buffer "*sleep test*"))
```

I don't know how to use it correctly. Can you give some good examples of using
this `:filter' handler, and explain it a little? 

Thanks in advanced.

- -- 
[ stardiviner ]
       I try to make every word tell the meaning what I want to express.

       Blog: https://stardiviner.github.io/
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Re: [QUESTION] How to use :filter in `make-process'?

[Joost Kremers]

On Tue, Mar 03 2020, stardiviner wrote:
> I have an code example try to use :filter handler of 
> make-process.
[...]
> I don't know how to use it correctly. Can you give some good 
> examples of using
> this `:filter' handler, and explain it a little? 

There is quite an elaborate explanation in the Elisp manual:

Elisp > Processes > Output from Processes > Filter Functions

or:

(info "(elisp) Filter Functions")  ⇐ put cursor here and press C-x 
C-e

HTH


-- 
Joost Kremers
Life has its moments

[SOLVED] Re: [QUESTION] How to use :filter in `make-process'?

[stardiviner]

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Thanks Joost.

After reading the Info manual (even though the Info manual is not very friendly.)

I have following source code example which works great.

#+begin_src emacs-lisp
(shell-command "touch /tmp/tail.log")

(let ((proc (make-process
             :name "*tail log*"
             :command (list "tail" "-f" "/tmp/tail.log")
             :filter (lambda (proc output)
                       (message "append log captured")
                       (let ((p (get-process "*tail log*")))
                         (when (buffer-live-p (process-buffer p))
                           (with-current-buffer (process-buffer p)
                             (let ((moving (= (point) (process-mark proc))))
                               (save-excursion
                                 ;; Insert the text, advancing the process marker.
                                 (goto-char (process-mark proc))
                                 (insert output)
                                 (set-marker (process-mark proc) (point)))
                               (if moving (goto-char (process-mark proc))))))))
             :sentinel (lambda (proc event)
                         (message "done!"))
             :buffer "*tail log*")))
  (display-buffer "*tail log*"))
#+end_src

#+RESULTS[<2020-03-04 00:15:51> 9c0b6b462a594bd21b9d5579bd9a9254a3279e62]:
: #<window 183 on *info elisp*>

Then execute following command to append content into the log file:

#+begin_src sh
for N in {0..10}; do
  echo $N >> /tmp/tail.log
done
#+end_src


- -- 
[ stardiviner ]
       I try to make every word tell the meaning what I want to express.

       Blog: https://stardiviner.github.io/
       IRC(freenode): stardiviner, Matrix: stardiviner
       GPG: F09F650D7D674819892591401B5DF1C95AE89AC3
      
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Re: [SOLVED] Re: [QUESTION] How to use :filter in `make-process'?

[Stefan Monnier]

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> After reading the Info manual (even though the Info manual is not very friendly.)

I suggest you `M-x report-emacs-bug` describing what you found
unfriendly, so the maintainers get a chance to improve it (tho of
course, what's friendly for one user can be very hostile for another
and vice versa).


        Stefan

Re: [SOLVED] Re: [QUESTION] How to use :filter in `make-process'?

[stardiviner]

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Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> After reading the Info manual (even though the Info manual is not very friendly.)
>
> I suggest you `M-x report-emacs-bug` describing what you found
> unfriendly, so the maintainers get a chance to improve it (tho of
> course, what's friendly for one user can be very hostile for another
> and vice versa).
>

I agree. The point I think unfriendly is where it does not have example with
:filter code example. The Info manual use other functions like
set-process-filter etc instead. Of course the Info manual already explained the
document about :filter though.

- -- 
[ stardiviner ]
       I try to make every word tell the meaning what I want to express.

       Blog: https://stardiviner.github.io/
       IRC(freenode): stardiviner, Matrix: stardiviner
       GPG: F09F650D7D674819892591401B5DF1C95AE89AC3
      
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Re: [QUESTION] How to use :filter in `make-process'?

[Stefan Monnier]

> (let ((op-fn (lambda () (message "call the fn"))))
>   (make-process
>    :name "sleep command test"
>    :command (list "sleep" "3")
>    :filter `(lambda (proc event)
>               (message "event catched!")
                                ^^^^^^^
                                caught ;-)
>               (funcall ,op-fn))
>    :buffer "*sleep test*"))

More importantly, the ,op-fn is incorrect, it should be ',op-fn
otherwise the value contained in op-fn will be re-interpreted as an
expression (which will sometimes be harmless but sometimes not,
depending on how the function value ends up represented).

Of course, the better solution is to use `lexical-binding` so you can
just write:

    (let ((op-fn (lambda () (message "call the fn"))))
      (make-process
       :name "sleep command test"
       :command (list "sleep" "3")
       :filter (lambda (proc event)
                 (message "event catched!")
                 (funcall op-fn))
       :buffer "*sleep test*"))


-- Stefan

Re: [QUESTION] How to use :filter in `make-process'?

[stardiviner]

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Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> (let ((op-fn (lambda () (message "call the fn"))))
>>   (make-process
>>    :name "sleep command test"
>>    :command (list "sleep" "3")
>>    :filter `(lambda (proc event)
>>               (message "event catched!")
>                                 ^^^^^^^
>                                 caught ;-)
>>               (funcall ,op-fn))
>>    :buffer "*sleep test*"))
>
> More importantly, the ,op-fn is incorrect, it should be ',op-fn
> otherwise the value contained in op-fn will be re-interpreted as an
> expression (which will sometimes be harmless but sometimes not,
> depending on how the function value ends up represented).
>
> Of course, the better solution is to use `lexical-binding` so you can
> just write:
>
>     (let ((op-fn (lambda () (message "call the fn"))))
>       (make-process
>        :name "sleep command test"
>        :command (list "sleep" "3")
>        :filter (lambda (proc event)
>                  (message "event catched!")
>                  (funcall op-fn))
>        :buffer "*sleep test*"))
>
Use lexical-binding in your example, it does not work. report error:

: error in process sentinel: Symbol’s value as variable is void: op-fn [2 times]

>
> -- Stefan


- -- 
[ stardiviner ]
       I try to make every word tell the meaning what I want to express.

       Blog: https://stardiviner.github.io/
       IRC(freenode): stardiviner, Matrix: stardiviner
       GPG: F09F650D7D674819892591401B5DF1C95AE89AC3
      
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Re: [QUESTION] How to use :filter in `make-process'?

[Michael Heerdegen]

stardiviner <numbchild@gmail.com> writes:

> Use lexical-binding in your example, it does not work. report error:
>
> : error in process sentinel: Symbol’s value as variable is void: op-fn
> [2 times]

Note that you need to bind the buffer-local variable lexical-binding to
a non-nil value before you eval the example.  Typically as file-local
variable in your source file.

Michael.

Re: [QUESTION] How to use :filter in `make-process'?

[stardiviner]

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Michael Heerdegen <michael_heerdegen@web.de> writes:

> stardiviner <numbchild@gmail.com> writes:
>
>> Use lexical-binding in your example, it does not work. report error:
>>
>> : error in process sentinel: Symbol’s value as variable is void: op-fn
>> [2 times]
>
> Note that you need to bind the buffer-local variable lexical-binding to
> a non-nil value before you eval the example.  Typically as file-local
> variable in your source file.
>
> Michael.

Aha, I see. Thanks Michael

- -- 
[ stardiviner ]
       I try to make every word tell the meaning what I want to express.

       Blog: https://stardiviner.github.io/
       IRC(freenode): stardiviner, Matrix: stardiviner
       GPG: F09F650D7D674819892591401B5DF1C95AE89AC3
      
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Re: [QUESTION] How to use :filter in `make-process'?

[Stefan Monnier]

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> Use lexical-binding in your example, it does not work.

What steps did you take to "Use lexical-binding"?


        Stefan

Re: [QUESTION] How to use :filter in `make-process'?

[stardiviner]

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Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Use lexical-binding in your example, it does not work.
>
> What steps did you take to "Use lexical-binding"?
>
>

I thought the lexical-binding is the let-binding.... Sorry, misunderstood.

- -- 
[ stardiviner ]
       I try to make every word tell the meaning what I want to express.

       Blog: https://stardiviner.github.io/
       IRC(freenode): stardiviner, Matrix: stardiviner
       GPG: F09F650D7D674819892591401B5DF1C95AE89AC3
      
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