Re: Redo/Undo (was: etags: M-. jump to the tag(called func), ...)

[Ilya Zakharevich]

[A complimentary Cc of this posting was sent to
B. Smith
<bpsm@aon.at>], who wrote in article 
<mailman.7386.1127026972.20277.help-gnu-emacs@gnu.org>:
> There is redo functionality it just doesn't present itself as a  
> separate action. If you interrupt a series of undo operations with an  
> editing operation

Sigh...  This was most probably beaten to death thousands times
already.  Of course I know of this poor-man workaround for missing
redo.  It is NOT A REPLACEMENT as far user-interface is concerned.  It
requires an exponential amount of keypresses w.r.t. situation when
redo is present.

With redo you can do the following (and I do it all the time):

  a) go back in time;

  b) Maybe I overshoot?  go forward in time a little bit.  No I did not;

  c) So I go back in time some more.

  d) Jump to b.

With emacs poor-man-workaround the undo-history starts snaking out
back-and-forth over the "real state history" so that the distance
between two points in "real history" grows exponentially in
"undo-sequence".

> I've gotten so used to it that I don't even notice it when I'm using  
> emacs anymore

They say that if all you have is a hammer, everything starts looking
like a nail

> though I confess I don't have as clear a mental model of what's
> going on as I'd like

Thanks for pointing out this.  This is *in addition* to the "logical"
problem above.  When you go linearly over the "snake" described above,
the direction of your "actual movement" is not predictable (am I
redoing or undoing now???).

(Even with simple undo/redo sequences, this strikes when undo hits the
start of the buffer; immediately you've lost whether you are undoing
or redoing.)

Hope this helps,
Ilya