bug#68863: Add support for using setf with seq-subseq

[Okamsn]

Okamsn wrote:
> Stefan Monnier wrote:
>>>> To avoid modifying more values than specified, that modifying function
>>>> uses a `when` condition. I'm not sure of a good way to stop `seq-do`
>>>> early when we know that it can stop calling the modifying function.
>>>> Normally, I would use `cl-block` and `cl-return`. Is it OK to use those
>>>> features in `seq.el`? If not, is it worth adding something like a
>>>> `seq-map-while` or a `seq-do-while`?
>>
>> `seq.el` is used by some parts of the implementation of `cl-lib`, so
>> the use of `cl-lib` risks introducing a circular dependency.  Maybe using
>> `cl-block/return` would be OK, but I wouldn't be surprised if it causes
>> bootstrap trouble.  You can use catch/throw, OTOH.
>>
>>
>>           Stefan
>>
> 
> Attached is an updated version using `catch` and `throw`. Thank you for
> pointing those out to me. The patch is also changed to signal
> `args-out-of-range` for the start and end indexes to be more like
> `seq-subseq`.
> 
> How does it look?

Hello,

After testing it more, I see that what I've written does not work as I 
expected in the case

(let ((v    (vector (vector 0 1)
                     (vector 2 3)
                     (vector 4 5))))
   (setf (seq-subseq (seq-subseq (elt v 0) 0) 0)
         [10])
   v)

in which I would expect it to replace the first element of the first 
sub-vector with 10. I will take more time to continue working on this.

Thank you for your patience.