bug#67456: [PATCH] seq.el: Add functions for mapping over subsequences

[Okamsn]

Okamsn wrote:
> Hello,
> 
> The attached features work like `cl-maplist` and `cl-mapl`, applying
> functions to a sequence and to the remaining parts of a sequence.  For
> example, `(seq-mapsub #'identity [1 2 3])` returns `([1 2 3] [2 3] [3])`.
> 
> The patch adds a `seq-mapsub`, `seq-dosub`, and a `seq-doseqsub`,
> similar to `seq-map`, `seq-do`, and `seq-doseq`, respectively.
> 
> I was looking for an equivalent for vectors of `cl-maplist`, `cl-mapl`,
> and `cl-loop`'s `for VAR on LIST`, and think that these would be useful
> additions.
> 
> To get the sub-sequences, the code uses `seq-rest` and stops when the
> returned sub-sequence is empty according to `seq-empty-p`.  This is
> similar to how I would do it for a list, using `cdr` and `null`, but is
> that a good way to do it for arrays and other sequences?
> 
> Thank you.

I've updated the patch to only add the one `seq-mapsub` function, to be 
more like `seq-mapn` and `seq-mapcat`, and to add an optimized version 
for lists.

Would you like anything changed?

Thank you.

v2-0001-Create-function-seq-mapsub-for-mapping-over-subse.patch
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