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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: Fri, 5 Jan 2018 13:34:48 +0000
User-agent: Mutt/1.7.2 (2016-11-26)

Hello, Eli.

On Fri, Jan 05, 2018 at 15:00:21 +0200, Eli Zaretskii wrote:
> > Date: Fri, 5 Jan 2018 11:41:07 +0000
> > Cc: address@hidden, address@hidden
> > From: Alan Mackenzie <address@hidden>

> >     The "complex primitive" case can be distinguised from the "atomic
> >     primitive" case because either the call to `after-change-functions'
> >     is missing (i.e. there are two consecutive calls to
> >     `before-change-functions'), or in the first call to
> >     `after-change-functions', `OLD-LEN' is less then `END' - `BEG' in
> >     `before-change-functions'.

> > The above leaves unsaid what happens when a "complex primitive" happens
> > to call b-c-f and a-c-f as though it were an "atomic primitive".

> It also provides no way to know, up front, whether a given primitive
> I'm about to call, is one or the other.  IMO, we need some way of
> doing that, if we want to document this distinction.

Do we really need this level of detail?  My idea was to enable users of
b-c-f and a-c-f to predict what they're going to be being hit with.

There are two patterns of handling b/a-c-f, the "atomic" and the
"complex".  My above proposal documents enough for somebody using
b/a-c-f to be able to handle the "atomic" and "complex" uses.

Why does that hacker need to know exactly what each buffer-changing
primitive does, or which falls into which category?  Surely it is enough
that she handle the b/a-c-f calls appropriately.

What am I missing here?

Alan Mackenzie (Nuremberg, Germany).

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