From: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: AMackenzie@harmanbecker.com, emacs-devel@gnu.org, rudalics@gmx.at
Subject: Re: AW: font-locking and open parens in column 0
Date: Fri, 10 Nov 2006 23:52:50 -0500 [thread overview]
Message-ID: <jwv64dmy5p0.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <E1GiiL2-0006E1-LT@fencepost.gnu.org> (Richard Stallman's message of "Fri\, 10 Nov 2006 21\:11\:20 -0500")
>> The purpose of open-paren-in-column-0-is-defun-start is to enable to
>> disable this heuristic. Setting it to nil disables the heuristic.
>> So I think his change is correct.
> Huh? What do you mean by "heuristic".
> Emacs is looking for an open-paren at top level in list structure.
When? We're talking about a patch to beginning-of-defun, right?
Beginning-of-defun has until now been defined by regexps.
> The heuristic is to take an open-paren at column zero and assume
> it is at top level.
The docstring of beginning-of-defun doesn't say anything about "toplevel".
AFAIK beginning-of-defun is a function in the same category as
forward-paragraph and things like that, which do not care much about the
global syntax state, but instead only pay attention to the immediately
surrounding text.
> I am having trouble relating the rest of your message to this issue.
> This is just a matter of implementing
> open-paren-in-column-0-is-defun-start = nil to do what it says it will do.
The discussion about beginning-of-defun is intricately tied to syntax-ppss
because:
1 - it started with a bug-report about wrong font-locking because
beginning-of-defun is apparently used by cc-mode to get a safe starting
point for syntactic analysis.
2 - beginning-of-defun has been used as a syntax-begin-function in several
occasions, as a heuristic to find a safe starting point for
syntactic analysis.
3 - changing beginning-of-defun to use parse-partial-sexp (or worse
syntax-ppss) defeats the purpose of using it as a syntax-begin-function.
It may even break such uses (e.g. in emacs-lisp-mode).
4 - the original motivation for the patch (i.e. point 1 above) is better
addressed by not using beginning-of-defun and rely on syntax-ppss's
cache instead.
I think the problem is that beginning-of-defun has many different possible
uses, not all of which are compatible:
1 - it can be used as a "move to toplevel" (i.e. outside of any syntactic
element). Currently it's a not reliable way to do that, but it's been
used as a good heuristic. Note that in some languages such a concept
may not even be very meaningful: in languages whose files are commonly
composed of only one toplevel element (typically a module or a class
which then contains other elements inside themselves maybe classes or
modules, ...).
2 - it can be used as a form of "backward-paragraph-for-prog-langs", to move
to the beginning of a "block of text". In case where defuns can be
nested, this first only move to the beginning of the nested defun.
3 - a mix of the two: define some level of nesting (if any) as the main one
(typically either the toplevel one, or if the toplevel is a single
element, use the next level down) and move to the beginning of the defun
at that level.
Interactive use mostly wants behavior 2 or 3.
A reliable way to get behavior 1 is to use syntax-ppss rather than
beginning-of-defun.
The proposed patch basically tries to make beginning-of-defun follow the
behavior number 1 and to make it do so reliably. Given the availability of
syntax-ppss to get the same result, I don't think this patch is such
a good idea.
OTOH it might be a good idea indeed to change beginning-of-defun so that it
ignores regexp-matches if they're inside comments or strings. But that'd be
a different patch, which would apply regardless of
open-paren-in-column-0-is-defun-start.
Stefan
next prev parent reply other threads:[~2006-11-11 4:52 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-03 8:44 AW: font-locking and open parens in column 0 Mackenzie, Alan
2006-11-03 14:02 ` martin rudalics
2006-11-03 14:14 ` Stefan Monnier
2006-11-04 6:38 ` AW: " Richard Stallman
2006-11-10 17:49 ` Stefan Monnier
2006-11-11 2:11 ` Richard Stallman
2006-11-11 4:52 ` Stefan Monnier [this message]
2006-11-12 5:14 ` Richard Stallman
2006-11-12 5:14 ` Richard Stallman
2006-11-12 19:45 ` martin rudalics
2006-11-13 17:16 ` Stefan Monnier
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