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

[Dmitry Gutov]

On 16/11/2023 16:36, Augusto Stoffel wrote:
> > That breaks any sequence type based on lists.  This is exactly the
> > problem I was raising with too-many-generic interfaces, btw.
> Good point.  IMO you just can't have both lists and "types based on
> lists" to work together properly; if we defined a method for
> seq-difference on lists, the issue would be the same (I guess that's the
> caveat you raised regarding Dmitri's patch).

Actually, we might not allow custom sequences based on lists to begin 
with. E.g. if there are two definitions

 (cl-defmethod seq-length ((l (head :m6-sparse)))

and

 (cl-defmethod seq-length ((l list))

...is there a well-defined ordering between them which would determine 
the one that will be used for (cons :m6-sparse nil)?

If not, the optimization proposed by Augusto should be quite valid. And 
whatever custom sequences are added later, should use cl-defstruct or 
similar.

> > Try Dmitry's patch instead, the one containing seq-difference-3.
> That approach is fine, but it only addresses one function at a time.
> (If we go that way, I suggest starting by the most useful ones:
> seq-filter, seq-some and seq-reduce.)

My patch should help all the set operations (difference, union, 
intersection). And seq-uniq too.

Anyway, there is no reason not to use both optimizations together.