Re: Predicate for true lists

[Eli Zaretskii]

> Cc: address@hidden
> From: Paul Eggert <address@hidden>
> Date: Fri, 6 Jul 2018 11:04:55 -0700
> 
> Eli Zaretskii wrote:
> > Do we really want this usage of the function as a predicate?  I find
> > this slightly unnatural,
> 
> Me too, but we haven't come up with a better function semantics, so let's 
> just 
> live with them. I don't care whether the function is called 
> proper-list-length 
> or proper-list-p. (As Drew mentioned, we could have both names.)

I'd prefer proper-list-p, as this is going to be by far the most
frequent use of the function, as evidenced by the patch.

> > and also not future-proof enough, because you
> > rely on the checks 'length' does internally.
> 
> I see now that those checks of 'length' were documented incorrectly, so I 
> installed the attached documentation fix into the emacs-26 branch. It should 
> be 
> OK to rely on these checks (after all, they're documented correctly now :-).

Thanks, but the documentation still doesn't say that 'length' signals
an error for anything that is not a sequence, which is what
proper-list-p is relying on.