Re: XKCD/541 compliance, anyone?

[Marcin Borkowski]

Hi all,

so finally I sat down and finished my smiley code.  I have still three
questions left, though.  But first – the (deceptively simple) code.

--8<---------------cut here---------------start------------->8---
(defvar smiley-regex "[:;>B][,']?-?[][()]"
  "This regex should match smileys, and only them.")

(defface smiley '((t :foreground "gray"))
  "Face for displaying smileys.")

(setq parse-sexp-lookup-properties t)
(add-to-list 'font-lock-extra-managed-props 'syntax-table)

(defconst smiley-props `(face smiley syntax-table ,(string-to-syntax ".")))

(define-minor-mode xkcd-541-mode
  "Toggle XKCD/541 mode.  In this mode, smileys (as defined by
smiley-regex) are treated as punctuation by Emacs movement
commands etc.  In particular, parens in smileys are skipped by
paren-matching commands."
  :lighter " :)"
  (if xkcd-541-mode
      (font-lock-add-keywords nil `((,smiley-regex . smiley-props)))
    (font-lock-remove-keywords nil `((,smiley-regex . smiley-props)))))
--8<---------------cut here---------------end--------------->8---

And now the questions.

1. In this post:
http://lists.gnu.org/archive/html/help-gnu-emacs/2015-01/msg00005.html
I noticed that syntax-propertize makes parse-sexp-lookup-properties
buffer-local.  OTOH, in the next post
(http://lists.gnu.org/archive/html/help-gnu-emacs/2015-01/msg00008.html),
Stefan Monnier confirmed my suspicion that the performance hit from
setting it globally to t is negligible.  Since I ended up not using
syntax-propertize – I think font-lock is better, especially that I also
want my smileys to be greyed out – I have to set
parse-sexp-lookup-properties manually.  Should I do it in my mode toggle
function, remembering the previous value and resetting it after
disabling the mode?  (More or less the same question concerns
font-lock-extra-managed-props.)

2. After enabling xkcd-541-mode, I have

,----
| (t
|  (("[:;>B][,']?-?[][()]" . smiley-props))
|  ("[:;>B][,']?-?[][()]"
|   (0 smiley-props)))
`----

as the value of font-lock-keywords.  Why does that look that strange?
Moreover, after /disabling/ the mode, the value of font-lock-keywords is
(t nil).  Strange, isn’t it?  Shouldn’t it be just nil?

3. The mode works – sort of, since there is one (a bit annoying) thing.
When I turn it on, and type this:

(hello world;-))

sometimes the opening paren is highlighted when typing the smiley (this
happens e.g. in emacs -Q after loading that mode), and sometimes not
(e.g. while I’m writing this message).  Why might that be so?

Best,
Marcin




On 2014-12-04, at 22:16, Marcin Borkowski <mbork@wmi.amu.edu.pl> wrote:

> Hi there,
>
> it is so frustrating to be unable to use paren matching (like in
> show-paren mode, or C-M-f & friends) when I use smileys.  And this
> *does* happen; comments in, say, elisp-mode seem to be safe, but in
> LaTeX smileys do break my workflow.  Try entering this in AUCTeX:
>
> \textbf{Hello :-)}
>
> then put the point at the EOL and press C-M-b.
>
> I have a dream: to have the s-exp functions ignore closing parens,
> brackets etc. /after/, say, things matching
>
> [;:B]-?
>
> (this regex should probably cover the most basic cases).
>
> AFAIK, these functions are deeply hardcoded in Emacs; its behavior here
> seems to be inborn and instinctive rather than learned and reflective,
> so to speak.  (I.e., it is based on the `scan-sexp' function, which is
> written in C rather than Elisp.)  I imagine that redefining scan-sexp in
> Elisp is possible, but there might be problems with performance.
>
> Did anyone try that?  Am I the only one with this problem, actually?


-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University