Re: using command-error-function in emacspeak

[Jarek Czekalski]

W dniu 2013-11-05 15:07, Stefan Monnier pisze:
> > > add-function is the to modify the behavior of a function.
> > > It can't know what `nil' represents.
> > This is what nil represents:
> > (defun nil-fun () nil)
> No, it's not.
> Try to (setq command-error-function #'nil-fun)
> to see if it's really the same as nil.

Do you mean some subtle elisp difference (which I do not see) or the way 
command-error-function works? Or you just caught me that I didn't 
include "&rest args" in nil-fun definition?

I know that (setq command-error-function 'nil-fun) changes Emacs 
behaviour, but this is not the case. I think the case is that

(add-function command-error-function something) ;; forgive me wrong 
syntax here

should do the same as

(setq command-error-function something)

in case when command-error-function is nil beforehand.

And the latter would be equivalent to:
(setq command-error-function 'nil-fun)
(add-function command-error-function something)
which is what I propose as a simplification of what add-function should do.

Please explain, what you had in mind. I still don't understand why 
add-function couldn't work on nils. Could you give one counter-example?

Thanks,
Jarek