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Re: Lisp primitives and their calling of the change hooks

From: Alan Mackenzie
Subject: Re: Lisp primitives and their calling of the change hooks
Date: Wed, 10 Jan 2018 19:48:39 +0000
User-agent: Mutt/1.7.2 (2016-11-26)

Hello, Stefan.

On Wed, Jan 10, 2018 at 14:30:12 -0500, Stefan Monnier wrote:
> > It's debatable whether it's within the rules or not.  The rules, which
> > we so carefully crafted a few days ago, say, in part; "The arguments to
> > `before-change-functions' will enclose a region in which the individual
> > changes are made, ...".  There will never be any changes made in the
> > quasi-deleted region, so to leave it without a balanceing a-c-f call
> > could be construed as against the rules.

> If so we should clarify the rules to allow for it.

Why?  I mean, why should we allow this?  What does it gain us?

> `upcase-region` will call b-c-f before knowing whether any char will
> be upcased, and I think we do want to allow that kind of behavior.

At the moment, non-balancing b/a-c-f are used only in primitives which
can't change the length of the buffer - things like
translate-region-internal and upcase-region.  There might well be
advantages in keeping things that way, there surely are no
disadvantages.  Non-balanced change hooks necessitate special handling.

>         Stefan

Alan Mackenzie (Nuremberg, Germany).

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