I'd just like to say that I find B a bit misleading because you couldn't
tell that the first list ended, it could just have undef's at the end. I
like a because it doesn't add any data that wasn't there, of course that
could be a reason to dislike it too. On the other hand c makes a good option
when you want to work with infinite lists. Is this something that could be
modified on per use basis and we just choose one now as the default "they
didn't request a specific one so use this one).
After all that i think I agree on C specificaly because you can provide a
good code use of it and it doesn't add any data that wasn't there before. I
don't think it should ever lean towards (b) but them I bet someone else will
have an equaly good use of that. ;) So in the end I think some way of
chooseing would be good, with one option picked as standard.