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RE: Faking an active region

From: Drew Adams
Subject: RE: Faking an active region
Date: Sat, 3 Sep 2011 09:40:23 -0700

> I am writing a minor mode in which I want to remap
> `undo' to ALWAYS act as if a specific region was active
> and transient-mark-mode was on.

Your mention of a "specific" region and your code attempt suggest that it is
always the same region, or at least that the region start is always the same
(the end is always eob, apparently).

> So how would I go about "faking" this active region in Emacs 
> Lisp?

Eli> See region-active-p and push-mark.

I doubt that will help much.

This is I think something like what Deniz requested:

(defun reg-undo ()
      (narrow-to-region nima-prompt-end (point-max))
      (setq this-command  'undo)
      (condition-case nil (undo) (error nil)))))

You must set `this-command' to `undo'.

To work on a region, which might not be active, just use `narrow-to-region' (and
`save-restriction').  A `save-excursion' seems to be needed at least for the
case where changes (which won't be undone) were made outside the region.
Likewise, the `condition-case' (or `ignore-errors', if you prefer).

You might need to tweak this a bit - test with various scenarios (redo etc.).

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