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Re: generic buffer parsing cache data

From: Paul Pogonyshev
Subject: Re: generic buffer parsing cache data
Date: Sun, 1 Jul 2007 16:49:32 +0300
User-agent: KMail/1.7.2

Stefan Monnier wrote:
> >> > I propose that each point position could have "cached parsing data".
> >> > This would be an alist indexed with cache data identifier.
> >> Have you experimented with `syntax-ppss'?
> > I propose to add something generic.  For instance, Python mode needs to
> > know indentation level of blocks.  It seems that `syntax-ppss` doesn't
> > return it at all.  And adding everything that might ever be needed by
> > some XYZ mode seems counter-productive and complicates an already complex
> > function and its return value.
> 100% agreement.
> This said, I think it might make sense to combine the two so that
> syntax-ppss returns not just the parse-partial-sexp state but also some
> mode-specific data.  At least it's been in my TODO list for a while now.

That would be nice, but I see one possible non-trivial problem here.  I'm
not sure that `parse-partial-sexp' stores cached data where it is most
logical for the current mode.  So it might lead to worse cache performance,
because `parse-partial-sexp' might choose to store data in more sparse
positions in a buffer than its mode would prefer.  (However, I might be
wrong, there can be a way to influent this.)

Also, relying on `parse-partial-sexp' makes caching impossible or very
difficult for minor modes, because they don't generally have a say in
determining buffer syntax.


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