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Re: New hook before-region-change-functions wanted

From: John Wiegley
Subject: Re: New hook before-region-change-functions wanted
Date: Fri, 08 Sep 2017 16:07:37 +0100
User-agent: Gnus/5.130016 (Ma Gnus v0.16) Emacs/25.2.50 (darwin)

>>>>> "AM" == Alan Mackenzie <address@hidden> writes:

AM> I would like to implement a new abnormal hook,
AM> before-change-region-functions. It would be called just before a change in
AM> the buffer's restriction (i.e., from widen and from narrow-to-region) and
AM> each function on it would take two parameters, the beginning and end of
AM> the new region being set.

I'd call it before-change-restriction-functions, if we wanted the hook.  It
could have interesting uses beyond syntax-ppss too. I'm not sure, though.

AM> The reason I want it is as part of the solution to bug #22983 (syntax-ppss
AM> returns wrong result). I envisage two (or possibly more) mutually
AM> independent caches, and a switch being made to the appropriate cache when
AM> the region is changed. This switch would be made inside a function on
AM> before-change-region-functions.

I was talking to Stefan about syntax-ppss yesterday (in person!). He
acknowledged the bug in syntax-ppss, and said he would like to find a better
way to set the right stage for the fix, involving a more rational scheme for
narrowing (if I understood correctly). Perhaps I can encourage him to chime in
with what he was thinking, because I'd like to hear that before committing to
a new hook that solves one aspect of problem.

It'll likely be a few days before he's done traveling home and gets through
his backlog before we hear from him.

John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

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