Chopping the last element of a list

[emacsq]

If I want to do this then I can do, for example:

(prog1
(car (last mylist)) (setq mylist (nbutlast mylist)))

But here last and nbutlast walks the list twice unnecessarily.

Shouldn't emacs provide a function which does it in one step, so the list isn't 
walked twice?

E.g. (choplast mylist)

which returns a cons cell of (LAST . CHOPPEDLIST)

Of course, returning two values is not very lispy, but at least it could be 
more efficient.

Is there an existing function which does this in one step? If not, shouldn't 
there be one built-in emacs, for efficient manipulation of the list's end?