>> 	(defun desktop-init (_frame)
>> 	  (desktop-save-mode)
>> 	  (desktop-read)
>> 	  0)
>> 	(add-hook 'after-make-frame-functions 'desktop-init)
>
> Yes, I think so.  Although you may wish doing this only once, not
> after each frame creation (in which case, you should make the function
> remove itself from the hook variable).

Good point.

>> It seems that those functions are expected to return a number, hence the 0.
>
> Hmm... where did you see that they are expected to return a number?

Forget it, I had an error I cannot reproduce, must have been something else.