Re: Easy to add with push but not to the end of a list

[Emanuel Berg]

Stefan Monnier via Users list for the GNU Emacs text editor wrote:

>> Although it is easy to add to a list using push, it
>> currently looks hideous to be able to add to the end of
>> a list.
>
> That's because adding to the end of a Lisp list is
> a *bad* idea.

Let's make it as good as possible first ...

Why is the below O(N), because of `last'?

(defun push-last (elem lst)
  (let ((elem-lst (list elem)))
    (if lst
        (setcdr (last lst) elem-lst)
      (setq lst elem-lst) )
    lst) )

;; (setq nil-lst nil)
;;
;; (push-last 1 nil-lst) ; (1)
;;
;; (setq lst '(1 2 3 4))
;;
;; (push-last 5 lst) ; (1 2 3 4 5)
;;
;; lst ; (1 2 3 4 5)

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