Re: How does `undo` know that `keyboard-quit`has been called?

[Stefan Monnier <monnier@iro.umontreal.ca>]

> I would like to write a command that behaves like `undo`, that is: a command
> that reverses its behaviour when the user calls `keyboard-quit`. I have read
> the Lisp code for both `undo` and `keyboard-quit` and I can't understand how
> `undo` achieves such behaviour. (I know that I could always advise
> `keyboard-quit`.)

undo reverses its behavior after any other command than undo.
I.e. keyboard-quit is not special in this respect.  The only part that's
special about keyboard-quit is that if you use it like that, it
typically doesn't do anything else (well, it beeps).


        Stefan