bug#69709: `sort` interface improvement and universal ordering predicate

[Mattias Engdegård]

29 mars 2024 kl. 13.06 skrev Eli Zaretskii <eliz@gnu.org>:

> . The description of value< says "lexicographic order" about some
>   types, but I think that is not clear enough, and we should tell
>   explicitly how the comparison works in those cases.

That's a good point. Since it is standard terminology I will explain it in the 
manual but leave the doc string as it is -- this is our usual practice, right?

> . AFAICT, no ordering is defined for overlays, and I wonder why.  I
>   think this could be very useful; we certainly sort overlays in C in
>   several places.

Yes, the plan was to add ordering for more types as we figure out which ones 
are missing. Basically, if a type has a useful ordering that is well-defined, 
we should probably add it.

That's one reason why I didn't include overlays from the beginning: I couldn't 
easily find one obvious ordering that would make intuitive sense, and I'd 
rather leave them unordered than define something useless. Code that sorts 
overlays uses a variety of criteria: priority, starting position, 
application-specific properties, and so on.

> . Various fine details about value< are never mentioned: the fact
>   that there's a limit to recursion, the special treatment of nil in
>   some cases, etc.  I think we should document them, at least in the
>   doc string if not in the manual as well.

Right -- the depth limit is very much like that of `equal` which is documented 
in the manual but not the doc string; I'll probably do the same for `value<`. 
`nil` deserves a note about its dual nature (symbol and list) as well.

Thank you for the markup fixes, by the way. One question:

> -@table @asis
> +@table @code

I used @asis because that is what the entries for some other functions using 
key-value arguments used, like `make-process`. Clearly the keyword should be 
marked up as @code, but should it encompass the @var{argument} part as well? Or 
should we use @asis and then explicit @code in each @item?