The Codeless Code: Case 150 Undone 
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 A monk asked master Kaimu, “What is the ideal behavior of
‘undo’?”

Kaimu answered, “To undo the last significant action of the
user, then the action before that, and so on to the
beginning of time.”

The monk asked, “What about the resizing of a window?”

Kaimu answered, “Ideally, that would be undone.”

The monk asked, “The saving of a file?”

Kaimu answered, “Also undone.”

The monk asked, “The sending of email?”

Kaimu answered, “Also undone.”

The monk laughed and said, “Absurd! How could anyone
implement such behavior?”

The master launched an application on this desktop. “Here is
an editor of my own devising, which implements the Ideal
Undo.”

The monk entered a line of text. Then he deleted a word,
resized the window, saved the file, and sent it as an email.
When the email appeared on his phone, he hit the editor’s
Undo key four times.

The monk said, “No effect.”

Kaimu answered, “Null. Time itself was reset to as it was
immediately after you entered your line of text. At which
point you—lacking all memory of the prior iteration—again
deleted the word, resized the window, saved the file, and
sent the email.”

The monk pointed triumphantly at the master. “Null to your
Null! For in the alleged second iteration I would have
subsequently hit Undo four times, just as I did in the first
iteration...thus creating an inescapable loop!”

Kaimu folded his arms and with satisfaction answered, “The
actions of the second iteration were not significant, since
they were fated to occur as a consequence of resetting the
clock; thus they are not candidates for the Ideal Undo. Only
your four Undo key-presses in the first iteration—the ones
which initiated the second iteration—were significant.”

The monk asked, “So what became of these four Undos?”

Kaimu answered, “Thanks to the four Undos in the second
iteration... also undone.”