Thank you. That's pretty neat, and I'm sure it'll be useful.
However, I feel it is addressing a slightly different point from my post. I can easily write my own library function to do, eg
(from-right '(1 2 3 4 5) 1)
I do feel the succinctness and power of the language would be enhanced by including the ability to instead call
('(1 2 3 4 5) -1)
Of course, other people may have a differing opinion.
Implementation is rather simple... you could essentially take all indexes mod the length of the collection. Although perhaps it just doesn't help that much outside of Project Euler :-)
