Using comment characters for specific major modes

[martin-kemp@brusseler.com]

I would find it useful if there was a function that returns a list with the comment delimiter 

for the specific mode.  Then one can select which one to get.



From: Omar Polo <op@omarpolo.com>
To: martin-kemp@brusseler.com
Subject: Re: Using comment characters for specific major modes
Date: 06/06/2021 10:34:12 Europe/Paris
Cc: help-gnu-emacs@gnu.org

I've seen only now the reply from Stefan Monnier, which is (of course
:P) better than mine, apologies. His explanation is indeed better.

Sorry for the noise.

Omar Polo <op@omarpolo.com> writes:

> martin-kemp@brusseler.com writes:
>
>> Am using the following expression to make a line composed of ";" of length lena.
>>
>>
>>
>> The first two semicolons ";;" are for when I use elisp code.
>>
>>
>>
>> (setq-local s (concat ";; " (make-string lena ?\;)))
>>
>>
>>
>> But I want to change the starting ";;" to be the comment character of the major mode I am working with.
>>
>>
>>
>> For texinfo I want "@c", and for fortran-mode I want "c", and "!!" for f90-mode.
>
> taking a look at how things like `comment-dwim' is quite educational.
> The comment handling is easy but there are a few gotchas, like not all
> major-modes have a single "comment string" (like ";" in Lisp), some have
> starting and ending comment string (like C with /* and */)
>
> I've come up with the following
>
> --------8<--------
> (defun insert-lena ()
> (interactive)
> (let* ((lena 8)
> (s (make-string lena ?\;)))
> ;; this bit is stolen from comment-dwim
> (if comment-insert-comment-function
> (funcall comment-insert-comment-function)
> (let ((add (comment-add nil)))
> (indent-according-to-mode)
> (insert (comment-padright comment-start add))
> (save-excursion
> (unless (string= "" comment-end)
> (insert (comment-padleft comment-end add)))
> (indent-according-to-mode))))
> ;; insert the string
> (insert s)))
> -------->8--------
>
> that seems to works.
>
> It uses comment-insert-comment-function or comment-start/end. I stolen
> a bit from comment-dwim.
>
> In lisps buffer it inserts
>
> ;; ;;;;;;;;
>
> while in a C buffer it adds
>
> /* ;;;;;;;; */
>
> Probably it doesn't do exactly what you want, and there are probably
> edge cases when there is a region active or things like that, but it's a
> good start (I think).
>
> HTH