Re: Using comment characters for specific major modes

[Omar Polo]

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