Re: Setting the nth element of a list

[Nordlöw <per.nordlow@gmail.com>]

On Jun 5, 4:25 am, Barry Margolin <bar...@alum.mit.edu> wrote:
> In article
> <8a7c4d36-195d-4517-827e-7fbeca7ae...@r34g2000vba.googlegroups.com>,
>
>  Nordlöw <per.nord...@gmail.com> wrote:
> > This simple example changes the second element in the list x:
>
> > (setq x '(a nil c))
> > (setcar (cdr x 'b)
>
> > How do I generalize this to a function that sets (changes) the nth
> > element of a list (for side effects only)?
>
> > Thanks in advance,
> > Nordlöw
>
> (require 'cl-macs)
> (setf (nth n x) 'b)
>
> --
> Barry Margolin, bar...@alum.mit.edu
> Arlington, MA
> *** PLEASE post questions in newsgroups, not directly to me ***
> *** PLEASE don't copy me on replies, I'll read them in the group ***

Okey, here is my solution:

(defun setnthcar (n list x)
  "Set N:th element of LIST to X for side effects only."
  (setcar (nthcdr n list) x))

Comments on that?

How do I accomplish the same with arrays? Using aref I guess. Here is
my mockup that doesn't yet do what I want:

(defun setnthref (n array x)
  "Set N:th element of ARRAY to X for side effects only."
  (set (aref array n) x))

Thanks in advance,
Nordlöw