bug#70524: [PATCH] Fix `map-elt` with `setf` for subplaces

[Michael Heerdegen via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

okamsn@protonmail.com writes:

> On efficiency and maybe outside of the sub-place question, I used
> `seq-map` because I thought that it would be a good way to make sure
> that the generic sequence was only moved through once. For a
> hypothetical `seq-replace`, do you think it would be better to use a
> combination `seq-concat`, `seq-take`, and `seq-subseq` and to assume
> that they are efficient implementations for the generic version? Do you
> think that it would be better if there were different implementations
> for each combination of the built-in sequence types, like the checks
> `cl-replace` has for lists and arrays?

Probably yes, that would be the consequence.  Haven't thought about
whether `seq-replace' is something we want, though.

Michael.