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Better parse-partial-sexp; multiple major modes (was: Idea for syntax-pp
From: |
Daniel Colascione |
Subject: |
Better parse-partial-sexp; multiple major modes (was: Idea for syntax-ppss) |
Date: |
Sun, 31 Aug 2008 05:39:56 -0400 |
On Jul 27, 2008, at 10:50 AM, Alan Mackenzie wrote:
What I think really needs doing is to make this function
bulletproof: It
should work on narrowed buffers, it should give reliable elements 2
and
6, 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.
Such a thing would have to live on the C side of things, right? (With
the proliferation of with-this and inhibit-that options available to
Lisp, I don't see how one can easily and robustly catch all buffer
modification. Not to mention that no matter which of before-change-
functions and after-change-functions you used, you could still race
against other functions using the same facility.)
If this perfectly caching parse-partial-sexp lives in C anyway, why
not just call it parse-partial-sexp? Optimize parse-partial-sexp for
the case of start being 1 or (point-min). syntax-ppss becomes a simple
wrapper. Not only would it be possible to robustly catch all buffer
and context modification, but by optimizing the existing function, all
existing users would automatically win. I'd offer to write a patch,
but I don't know the core well enough to know how to "easily and
robustly catch all buffer modification".
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, ....).
After several attempts at using and understanding multiple major mode
facilities, I'm convinced the only way forward is core support for the
concept. Lennart's done a fine job with what's in Emacs currently. But
anything involving multiple major modes today is a quivering mound of
hacks. All the work Lennart's had to do to get modes playing nice with
each other is a testament to that.
Maybe a core solution could be something like this: in a given buffer,
each character has a chunk-name character property. You'd buffer-
locally map chunk names to major modes. For each chunk name, create a
buffer containing just the text assigned to that chunk. Make the major-
mode the major mode for the chunk buffer, and let that major-mode
handle fontification, keybindings, and so on. In the main buffer,
assemble the various bits from the chunk-buffers and allow the user to
navigate the combined buffer normally.
Keybindings with point at a particular character would just be the
keybindings present in that character's chunk-buffer. If you need
special keybindings common across all chunk buffers, just bind the key
in all the chunk buffers. If a given chunk needs placeholder text to
represent text of some other chunk, it should be possible add it to
that chunk buffer without affecting any of the others.
Anyway, this scheme is:
1) Robust - no messing around with variables, no tweaking fontification
2) Backwards compatible - a major-mode doesn't need to know it's being
used this way
3) Versatile - you can compose arbitrary modes this way, even
recursively
4) Conceptually simple (I hope)
Any thoughts?
- Better parse-partial-sexp; multiple major modes (was: Idea for syntax-ppss),
Daniel Colascione <=