Re: font-lock function matcher sample

[Arjan Bos]

Stefan Monnier wrote:
> > What I have currently is working correctly.  First I find a word.  If word,
> > limit and point are the same as the previous time the function was called,
> > I return `nil'.
>
>
> The fact that you need to compare with last search indicates that there's
> something fishy with your code.
>
>
> >       (while (and (re-search-forward beatnik-font-matcher-regexp limit t)
> >                   (not (= (beatnik-last-word-score) score-match))))
>
>
> Here you lose the information about whether the search succeeded or failed
> which the source of your problems.  I.e. if the search fails immediately
> (typically you've hit LIMIT) then (= (beatnik-last-word-score) score-match)
> will be true and your code will screw up.
>
> How about the code below instead:
>
> (defun beatnik-=-matcher-p (limit score-match)
>    "Tries to find a word whose scrable score matches score-match.
> If such a word was found, t is returned."
>    (let (found)
>      (while (and (setq found (re-search-forward
>                               beatnik-font-matcher-regexp limit t))
>                  (/= (beatnik-last-word-score) score-match)))
>      found))

This is almost what I intended. This sets `found' to `t' even when the 
asked for scrabble score via (beatnik-last-word-score) isn't found. But 
when I move the `and' into the `setq' it doesn't work, meaning that it 
locks itself fontifying.

(defun beatnik-=-matcher-p (limit score-match)
  "Tries to find a word whose scrable score matches score-match.
If such a word was found, t is returned."
  (let (found)
    ;; doesn't work:
    (while (and (setq found (re-search-forward
                             beatnik-font-matcher-regexp limit t))
                      (/= (beatnik-last-word-score) score-match)))
    found))

So, unfortunately, I'm back to my kludge with the global variable that 
keeps track of the last matched match.

> > Stephan and Alan, many thanks for helping me out.  Maybe your comments
> > should find their way to the doc-string or the info pages?
>
>
> From what I can see, your problems had nothing to do understanding how
> font-lock works.  But if you have a concrete suggestion for how to change
> the docstring, patches are welcome.

Well, what I really missed was a sample function. I think the one you 
posted could well serve as a template. The info page 
((elisp)Search-based Fontification.) had the needed input and output for 
the defun, but the doc-string for `font-lock-defaults' had neither. 
Maybe it could point to the info page?
Although the info page contains all the needed info, I can understand it 
now in hindsight, but the thing about `match-data' /was/ quite confusing 
for me.


And the biggest nuisance in figuring this out was that emacs crashed a 
lot when getting things wrong in the defun. It gave lots of `malloc' 
errors and `double free' errors. Which is, of course, not a pretty way 
to cancel fontifying ;-) .

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