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Re: Idea for syntax-ppss. Is it new? Could it be any good?
From: |
Stefan Monnier |
Subject: |
Re: Idea for syntax-ppss. Is it new? Could it be any good? |
Date: |
Sun, 27 Jul 2008 11:51:36 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux) |
>> 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 don't understand the detailed workings of the routine at the moment.
> I suspect that the slowness of all the lisp manipulation will outweigh
> the benefit of the caching, but I would confirm or refute that with
> the profiler before doing anything serious.
> 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.
> 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.
> it should give reliable elements 2 and 6,
If you really care about them, then I recommend you fix it in
parse-partial-sexp.
> its cache should be cleared when functions like `modify-syntax-entry'
> are called or parse-sexp-lookup-properties is changed, and the cache
> should be bound to nil on `with-syntax-table'. I actually think it
> could be useful to maintain several parallel caches, each for a
> different syntax-table (or an equivalence class of syntax tables). And
> so on. Basically, I would like `(syntax-ppss)' to tell me with 100%
> reliability, no ifs, no buts, whether I am at top-level, in a comment,
> or in a string.
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.
> 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?
> 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.
Stefan
- 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