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Re: Idea for syntax-ppss. Is it new? Could it be any good?
From: |
Alan Mackenzie |
Subject: |
Re: Idea for syntax-ppss. Is it new? Could it be any good? |
Date: |
Sun, 27 Jul 2008 19:20:45 +0000 |
User-agent: |
Mutt/1.5.9i |
Hi, Stefan,
On Sun, Jul 27, 2008 at 11:51:36AM -0400, Stefan Monnier wrote:
> >> Isn't that what syntax-ppss does?
> > It caches the state for several positions, but I don't think they're at
> > regular positions.
> C-h v syntax-ppss-max-span
> It's not exactly perfectly regular, but I don't think the difference
> matters.
I was looking at my 3Mb buffer, and it seemed they were at wildly
irregular positions. But I think I was seeing something which wasn't
really there.
> > partial-parse-sexp is blindingly fast. To scan an entire 3Mb C
> > buffer on my elderly 1.2 GHz Athlon takes 0.27s. That is why I
> > suspect that the lisping in syntax-ppss might need severe
> > optimisation. But again, it's only a hunch.
> When I wrote syntax-ppss, my main goal was to never be significantly
> slower than parse-partial-sexp. Even if it's not as fast as it could
> be if written in C (which is pretty much obviously true), that's not a
> reason to recode it in C.
Surely the goal should be to be significantly faster most of the time.
Presumably it achieves this in practice. The reason to recode in C
would be to make it fast enough, or to couple it up to things which
couldn't be done in lisp. But probably neither of these things is
needed.
> > What I think really needs doing is to make this function
> > bulletproof: It should work on narrowed buffers,
> That can be done, tho it needs extra info in order to know how to
> interpret the fact that it's narrowed.
Don't understand. The function is defined as the equivalent of
(parse-partial-sexp (point-min) pos)? You've said before that the
function is best not called when a buffer is narrowed. Couldn't we just
redefine it as (parse-partial-sexp 1 pos)? Then we could just put
(save-extension (widen ..... )) into syntax-ppss.
[ .... ]
> I think this will result in too many cache flushes and will make the
> code too intrusive or too ad-hoc. I'd rather have a
> syntax-ppss-syntax-table (and force parse-sexp-lookup-properties to t)
> if you want more reliable results.
Hey, syntax-ppss-syntax-table is a brilliant idea! In its doc string one
could say "after setting this, clear the cache by calling ...
(syntax-ppss-flush-cache 1)".
> > Also, Lennart is asking for it to work nicely with multiple major modes.
> > Surely this would be a Good Thing. Files containing several major modes
> > are commonplace (awk or sed embedded within a shell script, html
> > embedded within php, ....).
> Yes, that's a desirable extension.
> > At the moment, CC Mode applies a heuristic maximum size of strings and
> > comments, for performance reasons. Checking for strings and comments is
> > done so frequently that the mode uses elaborate internal caches. It
> > would be nice if this cacheing could move to the Emacs core.
> You can do it today. Have you even tried to use syntax-ppss before
> asking for it to be improved?
No. I think I've been scared by its vagueness (about narrowed regions)
more than anything. It's defined in the elisp manual as equivalent to
(pps (point-min) pos) rather than (pps 1 pos). It also uses
syntax-begin-function, which doesn't seem right, and wouldn't work well
in CC Mode; the only way s-b-f can give a cast-iron result is by calling
parse-partial-sexp, or syntax-ppss. In fact, if syntax-ppss was
bulletproof, syntax-begin-function would be redundant. I don't think
syntax-ppss is quite the right function for what I want to do. I need
something like it, but not identical.
Maybe I should test syntax-ppss by coding up inside a macro which
widens. And I've been less than convinced it's actually faster. In
fact, I'll go and do some speed tests and report back.
> > Again, this isn't something which can be implemented in a weekend,
> > but I think it would be worthwhile for Emacs 24.
> Other than the multi-major-mode part, it all sounds like very
> minor changes.
Maybe.
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).
- Idea for syntax-ppss. Is it new? Could it be any good?, Alan Mackenzie, 2008/07/26
- Re: Idea for syntax-ppss. Is it new? Could it be any good?, Lennart Borgman (gmail), 2008/07/26
- Re: Idea for syntax-ppss. Is it new? Could it be any good?, Stefan Monnier, 2008/07/26
- Re: Idea for syntax-ppss. Is it new? Could it be any good?, Richard M Stallman, 2008/07/27
- Re: Idea for syntax-ppss. Is it new? Could it be any good?, Stefan Monnier, 2008/07/28
- Re: Idea for syntax-ppss. Is it new? Could it be any good?, Richard M Stallman, 2008/07/28