Re: Syntax ambiguities in narrowed buffers and multiple major modes: a proposed solution.

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan

On Sat, Feb 25, 2017 at 14:42:06 -0500, Stefan Monnier wrote:
> Sounds fairly close to some of the ideas I toyed with.

Excellent!

> Here are a few comments:

> >   o - Ambiguity involved with narrowed regions - sometimes programs and
> >     users wish to see syntactic entities (e.g. strings, comments) as
> >     though point-min were a syntactically neutral position - other times
> >     they want the syntax to be relative to the beginning of the buffer.

> I don't think this need is very serious for users.
> So, I think we should focus on those cases where this is used by Elisp
> code.

I don't really see the distinction between users and code here.  If we
implement for one, it will work for the other, won't it?

> >   o - There will be two new syntax classes introduced for use in syntax
> >     table text properties: "island open" and "island close".  Together,
> >     these enclose an "island", a region of the buffer syntactically
> >     disjoint from the text outside of the region.

> [ I like to consider that strings and comments are also a form of
>   "island", although we're probably better off supporting them in
>   a special way like we do now.  ]

I think that's just confusing the meaning of "island", which I'd like to
keep clear and unambiguous.  Something to be decided is how we'd handle
an island within a comment or string.

> I think we should try not to limit ourselves to nesting of islands.
> IOW, we should strive to find a design where a single char can close an
> island and open another one.

That would need just a minor extension of what I set out, I think.
Something like an "island swap" syntax class.  This might find use in
languages like lex and yacc.

> >   o - narrow-to-region will be given an optional argument which, if set,
> >     directs Emacs to make the new region an island.  Thus, C-u C-x n n
> >     would enable a user to narrow to a "comment within a string" and edit
> >     it as though it were a comment.

> How would this work (especially for uses from Elisp)?
> Would it set syntax-table text-properties?

Yes, it would.  It would put an island open syntax-table property on the
character before START, and and island close on the character after END.
This would isolate the region syntactically from its surroudings.

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).