Scary undo

Scary undo

[Lennart Borgman (gmail)]

I would like to undo a change made by a function that I call with 
funcall. I do not know exactly what the function does, but hopefully it 
will only indent the current line. However the new indentation might be 
wrong.

The scenario is something like this

    (funcall the-indentation-function)
    (when (= 0 (current-indentation))
       ;; undo what `the-indentation-function' did,
       ;; but how?
       )

I am a bit scared of writing this undo part so if someone could help me 
I would be glad. I do not think I can use `undo-boundary' here.

Re: Scary undo

[Juanma Barranquero]

> I would like to undo a change made by a function that I call with funcall. I
> do not know exactly what the function does, but hopefully it will only
> indent the current line. However the new indentation might be wrong.

Perhaps you could use `atomic-change-group' and friends?

 Juanma

Re: Scary undo

[David Kastrup]

"Lennart Borgman (gmail)" <lennart.borgman@gmail.com> writes:

> I would like to undo a change made by a function that I call with
> funcall. I do not know exactly what the function does, but hopefully
> it will only indent the current line. However the new indentation
> might be wrong.
>
> The scenario is something like this
>
>    (funcall the-indentation-function)
>    (when (= 0 (current-indentation))
>       ;; undo what `the-indentation-function' did,
>       ;; but how?
>       )
>
> I am a bit scared of writing this undo part so if someone could help
> me I would be glad. I do not think I can use `undo-boundary' here.

I'd be tempted to do something like

(condition-case nil
  (atomic-change-group
     (funcall the-indentation-function)
     (when (=0 (current-indentation))
       (signal 'barfout)))
  (barfout))

-- 
David Kastrup

Re: Scary undo

[Lennart Borgman (gmail)]

David Kastrup wrote:
> "Lennart Borgman (gmail)" <lennart.borgman@gmail.com> writes:
> 
>> I would like to undo a change made by a function that I call with
>> funcall. I do not know exactly what the function does, but hopefully
>> it will only indent the current line. However the new indentation
>> might be wrong.
>>
>> The scenario is something like this
>>
>>    (funcall the-indentation-function)
>>    (when (= 0 (current-indentation))
>>       ;; undo what `the-indentation-function' did,
>>       ;; but how?
>>       )
>>
>> I am a bit scared of writing this undo part so if someone could help
>> me I would be glad. I do not think I can use `undo-boundary' here.
> 
> I'd be tempted to do something like
> 
> (condition-case nil
>    (atomic-change-group
>      (funcall the-indentation-function)
>      (when (=0 (current-indentation))
>        (signal 'barfout nil)))
>   (barfout))

Thanks David and Juanma, that was what I needed.