Re: paren-close-dwim: elisp function of a newbie; feedback welcome

["Andreas Röhler" <andreas.roehler@online.de>]

Am 25.09.2013 13:46, schrieb Florian:
> Hi,
>
> here is my first elisp function 'paren-close-dwim' and I would be glad
> to get some feedback on it (whether its done to complicated, in an
> unusual way, or whether this functionality is already available in
> some emacs extension which I have not found).
>
> The function allows to close braces/brackets/paranthesis without the
> user to care which kind of brace actually has to be closed next. For
> me this is much handier than using paren-mode or auto-pair etc,
> especially when modifying existing code. Automatic paren modes came in
> the way and did the wrong thing from time to time for me and I had to
> delete automatically inserted closing paranthesis which was hindering
> my workflow. So, to be honest, I were not able to master them
> appropriately enough with my muscle memory.
>
> I work with a German keyboard layout where braces are not that easily
> reachable as on the Englisch layout, but I want to stick with this and
> just want to avoid some uncomfortable key-strokes for closing braces.
>
> So, here is my function paren-close-dwim, which you can freely pick
> and use for your own configuration.  Maybe it is a bit
> 'over-commented', which only represents my still lacking elisp
> fluency.
>
> (defun paren-close-dwim ()
>    "Insert the next missing closing paranthesis based on the syntax table.
>     Otherwise insert a normal closing ?\)"
>    (interactive)
>    (save-excursion
>      (setq fallback-char ?\))
>      ;; go backward up a level in the parenthesis hierarchy (which
>      ;; jumps to the next not yet closed (seen from point) open
>      ;; parenthesis). Catch unbalanced paranthesis error etc.
>      (setq closing-paren
>            (condition-case nil
>                (progn (backward-up-list)
>                       ;; get character at point
>                       (setq open-paren (point))
>                       ;; get corresponding closing character from the
>                       ;; syntax table. (syntax-after open-paren)
>                       ;; delivers a cons cell with (OPEN . CLOSE), so
>                       ;; we need the cdr to match open-paren.
>                       (setq syntax-cons (syntax-after open-paren))
>                       (if (cdr syntax-cons)
>                           (cdr syntax-cons)
>                         ;; if cdr is nil use the fallback-char
>                         fallback-char))
>              (error fallback-char))))
>      ;; insert dwim parenthesis
>      (insert closing-paren))
>
> ;; I bind this to the normal closing paranthesis key and am quite happy
> ;; with its behaviour in several different modes since a few weeks now.
> (global-set-key (kbd ")") 'paren-close-dwim)
>
> Thanks for your feedback,
> Florian
>
>

Hi Florian,

IMO that's quite interesting, thanks.

In detail some design suggestions:

- use let-bound variables instead of setq closing-paren
- don't rely on syntax-table (xclusively), rather make it an universal command, relying on chars
   that would permit also to close "}" for example, being usable in text-modes.
   skip-chars-backward MY-DELIMITER_CHARS seems an option.

Andreas