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Re: Syntax tables for multiple modes [was: bug#22983: syntax-ppss return

From: Vitalie Spinu
Subject: Re: Syntax tables for multiple modes [was: bug#22983: syntax-ppss returns wrong result.]
Date: Sat, 19 Mar 2016 23:51:35 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.91 (gnu/linux)

>> On Mon, Mar 14 2016 22:06, Dmitry Gutov wrote:

> Hi Alan,

> On 03/14/2016 05:16 PM, Alan Mackenzie wrote:

>> How about an extension to the parse-partial-sexp (etc.) code?  For
>> example, a feature I would call an "island", where a character could be
>> marked with the "island start" syntax-table property, and another
>> character lower down could be marked with the "island end" character.

> Something like that might help, although I hesitate asking for that change
> because it's a relatively big one, and it would still solve only one
> multiple-mode-related issue.


> But we could have pretty much that already by advising syntax-ppss. That
> leaves out parse-partial-sexp, but it's not used that often directly in major
> mode code (though sgml-mode uses it).

You can simulate islands by marking inner spans as comments with comment classes
(11 and 12). I used those in polymode in the past, but not anymore. It's not
that useful. Most of the parsing that modes do is regex based. So if a mode
author decides to regexpf for a wiki link on a full buffer after widening it,
islands won't help.

As Dmitry mentioned, there is little multi-mode cannot do with advising
syntax-ppss. The issue is still that parse-partial-sexp blows with narrowed code
and you cannot advice it.

IMO the most useful direction for multi-modes is to add a hard narrowing that
Stephen mentioned in the other thread. `syntax-ppss-dont-widen` goes in that
direction, but it doesn't address the issue of distinguishing between user
narrowing and "hard narrowing" in multi modes.


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