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

[Emanuel Berg]

Heime 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.
>
> The bad idea comment disregards necessity.

Okay NOW it works ...

(defmacro push-last (elem lst)
  (if (and (symbolp lst)
           (not (symbol-value lst)) )
      (list 'setq lst `(list ,elem))
    (list 'nconc lst `(list ,elem)) ))

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

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