Re: An idea: combine-change-calls

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan.

On Tue, Mar 27, 2018 at 16:24:28 -0400, Stefan Monnier wrote:
> >> See http://elpa.gnu.org/packages/undo-tree.html
> > Interesting.  But I think it would be overkill for me personally.

> The point is not to make you use it, but that this package uses the same
> buffer-undo-list, so any change to the format would break it.

It would need amendment, of course, but that wouldn't be difficult.  But
I suspect that the mechanism you suggested (an `apply' format element
recursively calling primitive-undo), will break other packages too, even
if the format of undo lists isn't changed.  We'd have to try it out.

> > I really don't want to do this [combining all the undo elements into
> > a single undo element].  Some people will want to analyse
> > buffer-undo-list and such a replacement will throw off this
> > analysis, possibly to the extent of making it useless.

> How/why?  I can't think of any case where it would cause such problems:
> the resulting undo-list, tho less detailed than the original one, is
> perfectly valid.

You put it most eloquently yourself in Subject: Re: What improvements
would be truly useful?  Date: Thu, 08 Mar 2018 23:43:57 -0500:

    Of course Emacs can also hide information (as text-properties, as
    invisible text, as data stored in buffer-local variables, ...) but most
    packages follow a design where as little info as possible is hidden.
    Indeed, whenever I hide such information, I think it over many times
    because I know there's a very strong chance that users won't like it.

What we've been discussing goes beyond hiding information, it is the
destruction of information.  Users, maybe just a few, won't like that at
all.

Incidentally, position elements in the undo list don't work: `undo'
removes them from buffer-undo-list.  I think you amended that bit of
code some years ago.  Can you say why this is done?  The comment in the
code:

    ;; Don't specify a position in the undo record for the undo command.
    ;; Instead, undoing this should move point to where the change is.

doesn't give any reason, and the various pertinent commit messages
aren't any help either.

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).