Re: How can I undo a change from a modification-hook?

[Clément Pit-Claudel]

On 2017-04-26 14:43, Stefan Monnier wrote:
>>>>> In the case of PG, I'd suggest you treat such a case as
>>>>> a non-whitespace change.
>>>> But I can't, can I? The damage (the change) is already done at that point,
>>>> and I can't revert it.
>>> But you can "retract" until the beginning of the changed area.
>> No, not if the current subprocess is busy.
> 
> Not sure why it matters: you queue the retraction commands for execution
> when the subprocess is done with its current command(s).

No, that's not something that I can currently do: I can't queue a retraction 
before the processing of that section is complete (because that processing may 
fail, and then there wouldn't be anything left to retract).

Of course, I could rewrite the queuing logic to be more resilient to this kind 
of changes.  But the question is about ways to prevent edits, and I think it's 
more general than this particular example.