Re: master d62766305a: Add `take` and `ntake` (bug#56521)

["Mattias Engdegård" <mattiase@acm.org>]

18 juli 2022 kl. 10.48 skrev Robert Pluim <rpluim@gmail.com>:

> Does this need the usual blurb to do
> 
> (setq list-var (ntake 3 list-var))
> 
> to ensure `list-var' is updated?

Sort of; I added some text to that effect. Using the return value is only needed if N can be nonpositive.

> I think this would be clearer as
> 
> "If N is >= the length of LIST, return LIST (or a copy)."
> 
> since weʼre talking about the effect of various values of N.

Right, it's now been changed to something like that. Thank you!

Now `seq-take` uses `take`, and so does `seq-subseq`. This made both faster, but the latter was boosted immensely by not formatting an error string up-front.

`seq-subseq` would be even faster if simply written as

  (take (- end start) (nthcdr start sequence))

but the interface requirements force a much more cumbersome implementation. (And does it really need `copy-sequence`? The docs are unclear.)

I suppose that `seq-subseq` should use `cl-defmethod` for dispatching on type but I didn't change that part.