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The author isn't dismissing "window shopping". They're just dismissing the need to keep track of the "window shopping" in the history, since you're not changing anything in the history.

If you have state1, edit it and get state2, edit that and get state3, then go back to state2 and copy something and then go forward again to state3 to paste that something, why should the history from state3 (in reverse chronological order) then be [state2,state3,state2,state1] when it could just be [state2,state1]? This is what the author claims, and it makes sense to be. If I undo, don't make any changes, then redo, I don't want that undo-redo to then be part of the undo history.

This. To elaborate, the problem is that without the "window shopping" optimisation, you are forced to repeat all your "window shopping" excursions twice every time you want to go a little further back in time.

To illustrate how horrible this is, I'll continue the example: When you paste that something, you get state4. Suppose you then wanted to copy something from state1. Without the "window shopping" optimisation, you would have to go state4,state3,state2,state3,state2,state1, copy, state2,state3,state2,state3,state4, paste.

If you then wanted to copy something from state0, it would take 34 steps!

I might be understanding you poorly here...

The author is not dismissing this in the sense of saying “it's impossible and that's okay” but rather “it's possible and it never generated the ambiguity in the first place, so it needs no special logic.”

So you probably actually use undo-redo in two big ways:

1. I just pasted the wrong thing or modified the wrong file or the kid grabbed the keyboard etc, I want to quickly erase N changes.

2. I want to grab info from the past and surface it back to the present. I cut something and then lost my clipboard contents, or so. This is what you described.

The problem in the article is, basically imagine that you get the key wrong. You do your browsing thing, you are N levels back in time, but instead of Cmd-c to copy this block of code, you accidentally either Cmd-x which deletes it, or Cmd-v or Opt-c or so which overwrites it. You were trying to do (2) but now the dominant heuristic suggests to the computer that you are actually doing (1). Because in the usual implementation of undo-redo, undos push changes off the history onto a stack, redos pop changes off the stack onto the history... And any new change clears the redo stack! That stack clear is the heuristic providing the difference between (1) and (2). When the heuristic misfires, it misfires in really dangerous ways, potentially eating hours of work.

So (2) is not being dismissed as “who cares” but rather as “that's fine because our heuristic has not yet led us astray, every implementation of undo that has redo will solve obvious-(2) and obvious-(1) correctly.”

This is where I might be misunderstanding you, I am not clear if you are saying that your editor is cooler than this default interpretation in some way that does not require “redo all the way back and cut-and-paste the previous partial state”...? If so then I would have to hear more before I could know if the article’s “history is always chronological, but browsing history is different than undoing it: undoing it only happens on an edit to an old browsed copy and saves a history-rollback into the modern chronological history, rather than fussing with undo graphs or whatever” approach works that way.

Edit: actually, the article’s approach of having a browse mode solves your problem automatically in a counterintuitive way... Cut instead of copy, you will get launched out of browse-mode, then undo twice to get to the tip of your history. Counterintuitive but definitely saves some keystrokes.

Fundamentally, the example I’m bringing up requires a tree structure conceptually, mixing some older history with some newer history. The solution in the article doesn’t address this, and it seems to dismiss the need for this use case, but I’m saying the whole reason I get into a situation where knowing how undo and redo work, and when I might care about whether typing after redo will lose history, is because I’m trying to merge old state with recent edits. I want both changes, not just one or the other.

Have to disagree here. "History mix" is a super common use case for me, as is a "clip slip" scenario - where I fumble and erase the future.

The technique as described works fine for this. I use it in the terminal all the time (an interface where state is saved on execution rather than keystroke). You go up through the history, copy the part of the command you need and head back to the present to use it.

I think it just comes down to the point at which state is modified. I wouldn't expect an implementation to modify state just by viewing the history, only by editing it. Suffice it to say your use case is fine.

Edit: tho, reading some of your other comments I agree that a better interface for this use case (e.g. a "revert to last meaningful edit" action) would be useful. Tho its slightly tangential to the discussion.

It doesn’t sound like you have a problem though. Just keep doing what you’re doing.

Hehe, sure, but there are better ways to do this, and it’s a common need. If the best thing we have is hitting undo 45 times to find something, copy it, try not to accidentally type anything and try not to accidentally lose the clipboard, then redo 45 times, then do a bunch of manual editing… now repeat the entire process for every file, when there are several involved… if that’s sufficient, then SVN is sufficient for source control, and we have no need for Git, right? ;)

My real point is that the “Great Undo-Redo Quandary” is broader than what’s in the article, and the solution discussed is incomplete, doesn’t solve a big chunk of the reason people are using undo multiple times.

Is it though? If you really just needed part of what you had and hour ago, then there's nothing wrong with scrolling back to an hour ago, copying that one bit you needed, scrolling back some more to where you were a minute ago, and integrate it as desired?

(which, note, is not window shopping: you didn't go back to have a look and skedaddle; the past is a data store, and you're accessing that data store for productivity reasons)

I feel like it is, so I’m not sure what you’re asking. It’s sometimes error prone depending on editor, and sometimes a lengthy and manual hassle to undo many times & copy old state, and then to merge if it’s not a single contiguous block and not a single file. It’s way easier to do what I’m talking about if I’ve committed changes in git every 5 minutes, but I don’t always do that in advance (most people don’t), and therefore could be nice to have a non-linear undo UI that addresses the workflow example I’m talking about, which happens to be a common reason that people even think about what happens in multiple undo-redo scenarios in the first place. What’s wrong with pointing out that 1- we can make better tools if we want, and 2- linear undo/redo doesn’t solve the whole problem?

Doesn't sound like linear undo/redo is the problem, but rather ability to navigate it. Timestamp the actions and you could offer "undo to 1h ago". Or you could allow searching the undo history.

But I may be having a hard time understanding why you need this as your description just does not fit my typical workflow.

In the proposed article, it sounds like if you accidentally typed anything you would have to hit "undo" twice instead of "redo" N times to get back. Still seems confusing.

But if you accidentally type something now you can't just hit redo N times to get back. It's gone.

Not with this new algorithm.

"And everything goes back to the beginning"