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Re: Unbalanced change hooks (part 2)

From: Phillip Lord
Subject: Re: Unbalanced change hooks (part 2)
Date: Thu, 01 Sep 2016 07:40:01 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.95 (gnu/linux)

Stefan Monnier <address@hidden> writes:

>>> Note that in the subst-char-in-region you could "make it pairup"
>>> yourself by hand: if you have (< (+ start length) (cdr lentic--b-c-pos)),
>>> then you can just
>>>     (let ((diff (- (cdr lentic--b-c-pos) (+ start length))))
>>>     (cl-incf length diff)
>>>     (cl-incf end diff))
>>> such that (eq (+ start length) (cdr lentic--b-c-pos)).
>> So, this works because subst-char-in-region is guaranteed not to change
>> the size of the region right?
> No.  It works because a-c-f's arguments say "nothing was changed before
> START and after END", so it's always safe (conservative) to move START
> towards BOB or move END towards EOB (of course, when updating END you
> also need to update LENGTH correspondingly).

Okay, yes, I understand now, and yes, this should be conservative, in
the sense that it works for all changes, I guess. We are making the
assumption here that "start" is always consistent between b-c-f and
a-c-f, and that this is never maximal in one case and minimal in the


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