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Re: syntax table entries for comments

From: Arjan Bos
Subject: Re: syntax table entries for comments
Date: Wed, 10 Sep 2003 15:35:54 +0200
User-agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.4) Gecko/20030624

Stefan Monnier wrote:

The second one is a single-line comment that consists of two
hyphens, like:
  -- this is a comment.

Emacs does not properly support this, as you've discovered.
To bad. At least I won't have to look for it in the docs anymore.

(defvar nrx-mode-syntax-table nil
  "Syntax table in use in NRX-mode buffers.")

(defun nrx-create-syntax-table ()
  (if nrx-mode-syntax-table
    (setq nrx-mode-syntax-table (make-syntax-table))
    (modify-syntax-entry ?. "." nrx-mode-syntax-table)
    (modify-syntax-entry ?- ". 12b" nrx-mode-syntax-table)
    (modify-syntax-entry ?/ ". 14" nrx-mode-syntax-table)
    (modify-syntax-entry ?* ". 23" nrx-mode-syntax-table)
    (modify-syntax-entry ?\n "> b" nrx-mode-syntax-table)
    (modify-syntax-entry ?\' "\"" nrx-mode-syntax-table))

  (set-syntax-table nrx-mode-syntax-table))

Could you tell me the place from which this code was inspired so we can
fix it ?  It should look like:

   (defvar nrx-mode-syntax-table
     (let ((st (make-syntax-table)))
       (modify-syntax-entry ...)
       (modify-syntax-entry ...)

and the `set-syntax-table' is commonly done implicitly by

I found it via Emacs Wiki. On page, they link to the following mode tutorial:
which I followed and used as an inspiration.

Could you please enlighten me as to why your way is better? I'm no (e)lisp expert, but I'm doing allright with a bit of voodoo programming[1].

This works but also renders the combination -* and *- as comment start and
end, which is wrong. Could anyone please tell me what I'm missing?

Nothing, really, other than the fact that it's a limitation of current
syntax-tables.  You can either hack on src/syntax.c to add support for
such cases, or use font-lock-syntactic-keywords to recognize `--'
and mark it as a comment starter.
I tried the latter, but then strings within the `--' comment will undo the comment highlighting. So I'll try to voodoo hack src/syntax.c

Thanks a lot,

Arjan Bos

[1] voodoo programming: Change something and see if it works. Keep on changing things until it does what you want. This way I can change most sources with only a minimum of knowledge about the language it's written in, by repeating the constructs already used. Downside is of course that you don't learn new language constructs. ;-)

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