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Re: Errors in interactive commands

From: Stephen J. Turnbull
Subject: Re: Errors in interactive commands
Date: Wed, 03 Aug 2011 16:28:31 +0900

Andreas Röhler writes:

 > A move-forward at the end of the buffer isn't a wrong command as such, 
 > just will not be successful.
 > Therefor it should not be raised an error, just nil returned.

This is problematic, IMO.  Suppose you have a buffer which is supposed
to have an even number of objects in it, and you want to delete every
second then.  Then

  (goto (point-min))
  (while (not (eobp))
    (forward-object 2)
    (delete-object -1)))

DTRTs, including detecting the "incorrect state" of an odd number of
objects, and not deleting the first object on an incomplete last line.

If you're going to change the behavior of the movement commands here,
I think it would be better to have them return the number of objects
left to move over.  Then 0 would mean (complete) success (how Un*x-y!)

But this would be a major change.

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