Re: Negative nth index

[Stefan Kangas <stefankangas@gmail.com>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> In CL, it errors (ditto for nthcdr with negative index).  Same for (nth
>>> '(1 2 3) -1) in Clojure or (list-ref '(1 2 3) -1) in Scheme.
>> Stefan Monnier, any comments here?
>
> I don't see a strong argument in favor of making it index from the end
> rather than signal an error.

I'd make it signal an error like in CL, Clojure, and Scheme, but it
doesn't do that today, so the change would not be backwards-compatible.
So I'm not sure what to do here or how.

For reference, the current behavior is this:

    (nth -1 '(1 2 3))                     => 1
    (nth -2 '(1 2 3))                     => 1
    (nth -3 '(1 2 3))                     => 1
    (nth most-negative-fixnum '(1 2 3))   => 1