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Re: mutate list by appending a list (and similar for props)


From: Pascal J. Bourguignon
Subject: Re: mutate list by appending a list (and similar for props)
Date: Thu, 18 Sep 2014 18:53:49 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Michael Heerdegen <address@hidden> writes:

> Sam Halliday <address@hidden> writes:
>
>> > (setq list (append additional-list list))
>>
>> Thanks! But that's not ideal because it involves repeating the list
>> symbol (which can often be quite long).
>
> Try (cl-callf2 append additional-list list) instead, which expands
> exactly into the above expression.

No!


You want prependf:


(require 'cl) ; of course!

(define-modify-macro appendf (&rest args) append "Append onto list")

(let ((list '(1 2 3)))
  (appendf list '(4 5 6) '(7 8 9))
  list)
--> (1 2 3 4 5 6 7 8 9)



(defun prepend (dest-list &rest other-lists)
  (apply (function append) (append other-lists (list dest-list))))
(define-modify-macro prependf (&rest args) prepend "Prepend to list")

(let ((list '(1 2 3)))
  (prependf list '(4 5 6) '(7 8 9))
  list)
--> (4 5 6 7 8 9 1 2 3)


-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk


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