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Re: Extending lua-mode syntax table (report from help-gnu-emacs)

From: Stefan Monnier
Subject: Re: Extending lua-mode syntax table (report from help-gnu-emacs)
Date: Sun, 11 Apr 2010 16:15:46 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

> (defun lua-mode ()
>  ;; ....
>    (set (make-local-variable 'font-lock-defaults)
>                        '(lua-font-lock-keywords nil nil ((?_ . "w"))))

> (defvar lua-font-lock-keywords
>  (eval-when-compile
>    (list
>    ;; .....
>     ;; Long strings.
>     '("\\(?:^\\|[^[-]\\)\\(\\[\\(=*\\)\\[\\(?:.\\|\n\\)*?\\]\\2\\]\\)"
>       (1 "\""))

You want to use font-lock-syntactic-keywords.  E.g. (warning: 100%
guaranteed untested code ahead):

   (defun lua-mode ()
    ;; ....
    (set (make-local-variable 'font-lock-defaults)
         '(lua-font-lock-keywords nil nil ((?_ . "w")) nil
           (font-lock-syntactic-keywords . lua-font-lock-syntactic-keywords)))
   (defvar lua-font-lock-syntactic-keywords
      ;; .....
       ;; Long strings.
         (1 (if (null (nth 8 (syntax-ppss))) "\"") nil lax)
         (2 (if (nth 8 (syntax-ppss)) "\"") nil lax)))))

> (defun lua-syntax-status ()
>  "Returns the syntactic status of the character after the point."
>  (parse-partial-sexp (save-excursion (beginning-of-line) (point))
>                      (point)))

(save-excursion (beginning-of-line) (point)) can be replaced by

> (defun lua-string-p ()
>  "Returns true if the point is in a string."
>  (elt (lua-syntax-status) 3))

> As you can see, the parse-partial-sexp function gets a range of text
> from the start of the line until the point. The long strings can span
> multiple lines (in fact, that's the whole point). So I'm worried that
> the parse-partial-sexp doesn't have enough context to work with. Is
> this true? 


> If so, is there a work-around (other than parsing from the start of
> the buffer), or do I need to implement something clever and specific?

You'll probably want to use (syntax-ppss) as a replacement for
(lua-syntax-status), which does exactly the same thing except that it
parses the whole buffer, but uses caching internally to try and make it
still fast enough.


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