Programming challenge: Undo

[Harry Binswanger hb@xxxxxxxx]

The only significant feature I know of that other programs have but Xy
lacks is "undo." Yes, the UnDelete function is a little bit of that, but
now we have before us a great opportunity and challenge: write an XPL
routine that gives us at least 3 levels of undo.

Conceptually, I would think the melody would go a little like this . . .
Maintain "trailing versions" of the current file, in a separate window (or
separate launch of another iteration of Xy). I wouldn't store every
alphanumeric keystroke (since we're only going to have a few levels of
undo), but these prior-version files are updated maybe after every 20th
alphanumeric keystroke and before every command or function is executed.

The thing that make this feasible is the speed of modern hardware.
If this could be done by launching a separate Xy window and passing through
the changes, there could be nine trailing versions--i.e., 9 levels of undo.
There would be a need to format or display the trailing versions of the
file in some way that didn't confuse the user as to which--current or
trailing--he was looking at.
Actually, here's a radical suggestion: keep the trailing versions in
Notepad. That way, no one will be confused. Maybe U2's copy-and-paste to
Windows could be used here. I'm unclear on the details, but is Carl or
Robert interested in tackling this?
Once this mission is accomplished, the last barrier will be down to Xy's
becoming the industry standard. And we will no longer be taunted on the
school yard.



Harry Binswanger
hb@xxxxxxxx