Re: Programming challenge: Undo

[Harry Binswanger hb@xxxxxxxx]

Carl,
Per below, did you try it the way I suggested--i.e., saving trailing
versions automatically after certain (limited) functions/commands were
performed? I misspoke in saying it would be after *every* function, since
that would include every cursor movement. I'm thinking the real value is to
undo CIs. Of course, that could be accomplished by modifying the kbd file
to call SAVEBAK or AUTOFILE before each CI.
Reply to note from Harry Binswanger  Tue, 17 Jun
2008 15:23:12 -0400

> Conceptually, I would think the melody would go a little like
> this . . .

Whoa, Harry! What you're describing is way too complicated. For a
measly 3-level Undo? Not worth the candle, IMHO.

You're right, though, Undo via XPL -- a true Undo -- is a real
programming challenge. And, my guess is, an insuperable one. At
least, every time I've attempted it, I've failed (not that I've
tried recently). Perhaps Robert has succeeded, although if he has, I
wonder why there's no frame UNDO in U2. Maybe he hasn't tried. If
anyone can do it, he can.

There are several U2 routines that, together or separately, provide
the functional equivalent of a virtually unlimited Undo: SAVEBAK
(make automatically-named backup saves of any file); AUTOFILE
(ditto, in spades -- up to 36 automatically-named backups per
minute); RECAll (ABort and reCAll current file, i.e., undo all
changes made since last SAve); RD (save block deletions to a file,
automagically). Worth a look. There are probably others. For
example, you can use TMPFILE:

XPLeNCODE v2.0
b-gin [UNTITLED]
{<}IF{<}VA$WS{>}==1{>}[JM_]2.tmpfile/nv[Q2_]{<}SX51,{<}VADR{>
}{>}[BX_]sa {<}PV51{>}{<}PV50{>}[Q2_][BX_]wait[Q2_]{<}EI{>}
-nd
XPLeNCODE

> Once this mission is accomplished, the last barrier will be
> down to Xy's becoming the industry standard.

Oh, yes? And what industry might that be? Digital archeology?

Speaking of which (and apropos of nothing), I love Agatha Christie's
quip about the great advantage of being married to an archeologist:
The older you get, the more interesting you become.

--
Carl Distefano
cld@xxxxxxxx


Harry Binswanger
hb@xxxxxxxx