Re: [PATCH] seq.el: add seq-last for symmetry with seq-first

[Matúš Goljer]

> Wouldn't it make sense to add a specialised implementation for lists, to
> avoid recusing the list twice.

I can turn it into defgeneric with default implementation same as what I
provided and special instance for a list, that makes sense.  Although I
wonder what the performance impact is of the dispatch vs iterating a
list /shrug.

> A thing I notice is that seq-first is not consistent on the way it
> behaves if the sequence is empty.
>
>         (seq-first '()) ;=> nil
>
> while
>
>         (seq-first [])
>
> raises an error.  seq-last would have the same issue for vectors, except
> that it would attempt to index the position -1, which might be
> confusing?

I think for lists it should behave as `nth` or `elt`, so it gives nil.
I agree that the error with -1 for vector might be confusing.  Should we
instead raise our own (seq) error for empty vector with seq-first and
seq-last?  Not sure what would be the best way.

I should also add some tests, I've noticed there was a test file for
seq.  Should I resubmit this patch with the feedback incorporated to
bug-gnu-emacs@gnu.org instead?  I'm not sure if emacs-devel is the
place, sorry T_T.

-- 
Best regards,
  Matúš Goljer