bug#32125: 26; Doc of `seqp` versus `sequencep`

[Eli Zaretskii]

> Date: Wed, 11 Jul 2018 06:50:44 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> Neither the doc strings nor the descriptions in (elisp) `Sequence
> Functions' make clear what the difference is between these predicates.

I think it does:

     This function returns non-‘nil’ if OBJECT is a sequence (a list or
     array), or any additional type of sequence defined via ‘seq.el’
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     generic functions.
     ^^^^^^^^^^^^^^^^^

> (It's not even clear why `seq' was added.  What's that about?)

See above.  At least on the level your question was asked, the answer
is clearly there.

> And the name `seqp' seems like a bad choice.  the predicate names
> themselves should at least give some hint of the difference.

Is this a separate bug?  Is it really important?

> The doc for `seqp' should not just punt and tell users to go look in
> `seq.el' to figure out what it means: "or any additional type of
> sequence defined via 'seq.el' generic functions."

What would you suggest as a better wording?  The difficulty here is
that seq.el provides features that are inherently extensible, so I
don't think an exhaustive list can be given.  But I might be wrong.

> And in (elisp) `Sequence Functions' the entries for these two predicates
> should be right next to each other.

I don't see a compelling reason to have them adjacent, but I did add
some text in the description of each one of them to mention the other
one.

Thanks.