Re: New undo element (fun . args)

[David Kastrup <dak@gnu.org>]

storm@cua.dk (Kim F. Storm) writes:

> storm@cua.dk (Kim F. Storm) writes:
>
>>>   In what way does the undo process fail to work?  Where is the
>>>   bug?
>>
>> I'm not sure it is a bug in the undo machinery or the way I try to
>> use it in cua, or a combination...
>
> I have installed change to cua to use the new undo apply element.
>
> The problems reported earlier were just errors in my code.
>
> It turned out to be quite tricky to get the usage right as an apply
> function need to install a proper _redo_ entry which may not really
> do anything but re-install the original _undo_ entry etc.
>
>
> I also changed primitive-undo to install at most one dummy apply
> element.

A _lot_ of people are annoyed at the way `undo' also redos things.
For that reason, a package redo.el exists, and people get told about
it frequently on Emacs lists and groups.

I consider it likely that with the new changes, this package will no
longer work.  I also have detected the variable undo-no-redo (not
customizable, though) which wouls appear from its name and description
to solve one half of the problem, the remaining half being that an
actual redo command working in the opposite direction would be
required.

Even if we don't find an actual keybinding for that (one could see
what redo.el uses), using undo with a negative argument could be used
instead.

Since we are likely to break redo.el, wouldn't it be sensible to
provide the functionality from within Emacs once and for all?  It does
not seem like much would be missing for implementing this, and one
could even make do without an extra keybinding by using negative
prefixes to undo.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum