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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: |
Sat, 6 Jan 2018 15:18:39 +0000 |
User-agent: |
Mutt/1.7.2 (2016-11-26) |
Hello, Stefan.
On Thu, Jan 04, 2018 at 16:36:42 -0500, Stefan Monnier wrote:
> >> which is lax enough that any behavior could be argued to be acceptable.
> >> IOW I think it's too lax. We should probably try and fix it to reflect
> >> the fact that every change should be covered by the last preceding b-c-f
> >> and should be followed by a corresponding call to a-c-f (and this
> >> before the next call to b-c-f).
> > Is that quite right?
> Probably not quite.
> > The upcase-region call in my test had no a-c-f call, almost certainly
> > because there were no lower case letters in the buffer at the time.
> Indeed, there were no changes, so no need to call a-c-f.
> > From your answers in this thread, I'm thinking that every
> > primitive-call which could change the buffer will have exactly one
> > b-c-f and zero or more a-c-f's.
> Sounds about right, tho I expect some primitives might just call insert
> and delete a few times, thus calling b-c-f several times.
> > How about something like this to replace that paragraph from the elisp
> > manual?
> > The primitives which atomically insert or delete a contiguous chunk
> > of text into or from a buffer will call `before-change-functions'
> > and `after-change-functions' in balanced pairs, once for each
> > change. The arguments to these hooks will exactly delimit the
> > change being made. Calls to these primitives comprise the vast bulk
> > of buffer changes.
> > Other, more complex primitives aim to call `before-change-functions'
> > once before making any changes, then to call
> > `after-change-functions' zero, one, or several times, depending on
> > how many individual changes the primitive makes. The `BEG' and
> > `END' arguments to `before-change-functions' will enclose a region
> > in which the individual changes are made, but won't necessarily be
> > the minimal such region. The `BEG', `END', and `OLD-LEN' arguments
> > to each successive call of `after-change-functions' will accurately
> > delimit the current change.
> Looks good to me, thank you.
I've found a discrepancy. Just one. In (transpose-regions 1 10 11 20),
the hook calls are, in order, ((1 10) (11 20) (1 20 19)). The two
consecutive b-c-f's happen when the two regions are of equal size and
non-contiguous.
The cause of this is not hard to find: in Ftranspose_region, editfns.c
L5204, there are two calls to modify_text on consecutive lines. This
seems to be some sort of optimisation. It is not done elsewhere in
Ftranspose_region. I dare say this could be fixed easily.
> I think in the case of subst-chars-in-region we only call a-c-f one time
> (but with tighter bounds than those of the preceding b-c-f) rather than
> once per character that's substituted, so maybe "The `BEG', `END', and
> `OLD-LEN' arguments to each successive call of `after-change-functions'
> will accurately delimit the current change" promises a bit more than we
> deliver, although it depends on how we interpret "current change".
> In any case, the above is much better than what we have now and I think
> it gives a pretty good rendition of our intention.
Perhaps for Emacs-27, if we want to fix transpose-regions.
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).
- Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/03
- Re: Lisp primitives and their calling of the change hooks, Stefan Monnier, 2018/01/03
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/04
- Re: Lisp primitives and their calling of the change hooks, Stefan Monnier, 2018/01/04
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/04
- Re: Lisp primitives and their calling of the change hooks, Stefan Monnier, 2018/01/04
- Re: Lisp primitives and their calling of the change hooks,
Alan Mackenzie <=
- Re: Lisp primitives and their calling of the change hooks, Stefan Monnier, 2018/01/06
- Re: Lisp primitives and their calling of the change hooks, Eli Zaretskii, 2018/01/06
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/06
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/06
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/07
- Re: Lisp primitives and their calling of the change hooks, Eli Zaretskii, 2018/01/07
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/07
- Re: Lisp primitives and their calling of the change hooks, Alan Mackenzie, 2018/01/07
- [SUSPECTED SPAM] Re: Lisp primitives and their calling of the change hooks, Stefan Monnier, 2018/01/07
- Re: Lisp primitives and their calling of the change hooks, Eli Zaretskii, 2018/01/07