Re: What's missing in ELisp that makes people want to use cl-lib?

[Dmitry Gutov]

On 15/11/2023 01:52, João Távora wrote:
> On Tue, Nov 14, 2023 at 11:11 PM Dmitry Gutov <dmitry@gutov.dev> wrote:
>
> > Allow me to try to answer this again: special voodoo is probably not
> > allowed. What the specialized methods are supposed to do is implement
> > the same logic (described in the generic function's docstring) but in a
> > more efficient manner.
>
> But isn't my method just that?

It's a good style, but any specific project's requirements might differ, 
and libraries often have to get defensive against bad practices, too.

> Let's say the methods's is simpler,
> like this:
>
> (cl-defmethod seq-contains-p ((seq my-voodoo-seq)
>                                  (elt (eql :secret-voodoo)) &optional _tesfn)
>      ;; my-voodoo-seq always has :secret-voodoo.
>      t)
>
> Hard to be more efficient than that, right?  Then I could use
>
> (seq-difference '(1 2 3 :secret-voodoo 5) (make-a-voodoo-seq))
>
> And get any voodoo out.

Okay... so a voodoo seq contains the :secret-voodoo keyword (maybe once, 
maybe several times, but not any other element).

Then it must have a seq-do implementation that yields :secret-voodoo one 
or several times. And then the seq-contains-pred implementation will do 
right by it (the default one, not the specialization for lists).

> > This is not documented,
>
> You don't say? :-)  i think we should get started on documenting all
> these ad-hoc rules (sorry but in this case they are quite literally
> ad-hoc).  Better than nothing, I guess, since as to actually enforcing
> them, I think that train has left the station a long time ago and is
> now in a voodoo swamp in monkey island.

Not sure "enforcing them" is the right phrase: I wonder if there's ever 
been a change proposed to seq.el which would break them.

Anyway, documenting them sounds best. As soon as we can arrive on a 
phrasing that sounds clear to all interested parties.

> Anyway, I'll be back with more custom sequences soon.

Please do.