Re: [PATCH] Run hook when variable is set

[Kelly Dean]

Stefan Monnier wrote:
>> Without it, code which would be simply:
>> (let-with-hook ((hooked-var foo))
>>             (body))
>
>> would have to become:
>> (setq tmp hooked-var)
>> (setq-with-hook hooked-var foo)
>> (body)
>> (setq-with-hook hooked-var tmp)
>
>> That's cumbersome.
>
> No, if you really need it, it's a simple (cl-letf (((get-var) foo)) ...).

I'm lost.

> I think I'd rather have something yet a bit simpler:
> - extend the `constant' bit to allow a "hooked" value, for efficiency.
> Provide a function to set/unset this "hooked" annotation.
> - when setting a hooked var, call a global Elisp function

IIUC, you mean you want a centralized handler for all hooked vars, rather than 
enabling use of separate functions for different symbols like varhook does.

>> That would fail in this case:
>> (setq-default cursor-type 'bar)
>> Later in the same Emacs session...
>> (dynamic-cursor-mode)
>
> As I already said, enabling dynamic-cursor-mode should set cursor-type to t.

Come on. I acknowledged that just two lines later in my message. Please don't 
imply that I ignored it.

>> then it won't work. If you instead do:
>> (make-local-variable 'dynamic-cursor-mode)
>> (dynamic-cursor-mode)
>> then DCM is enabled only locally,
>
> Not really.  Such usage is unsupported.  Users who do that get what they
> deserve.

Even though in the very next paragraph I showed a simple way to handle it 
properly even using your preferred way of implementing DCM?

IOW, you would intentionally omit that proper handling just for the sake of 
aggravating users who want to control DCM buffer-locally?

>> This has the edge case that if the mark happens to be active when you set
>> cursor-type to 'bar, then the setting doesn't stick;
>
> That's right.  I'm not worried about that either.

Well yeah, I guess you can just declare it to not be a bug.

This reminds me of the joke: How many Microsoft programmers does it take to 
change a lightbulb?
Answer: none. They just change the standard to darkness.


And what about the fact that your way of implementing DCM shows the mode as 
enabled, even though it effectively isn't, if the user set a non-standard 
cursor-type in his init file? I guess you think that's user-friendly too.

Splitting «technically enabled» from «actually in effect» results in a bad API 
too. For any other mode foo, if you want to know whether the mode is in effect, 
there's a variable to tell you, so the only expression you need is simply:
foo

But for your version of DCM, there's no such variable, so you would require the 
special-case expression:
(and dynamic-cursor-mode
     (or (eq cursor-type t)
         (and dynamic-cursor-mode--set (eq cursor-type 'bar))))