Re: How could I modify list element?

[richardeng]

Alan Mackenzie wrote:
> On Tue, 9 Dec 2008, richardeng wrote:
>
> > Hi all,
> >    setcar/setcdr is not convenient.
> >    In a long list, ex.
> >    (setq a '(a b c d e f g))
> >    I want to change 'e to 'E.
> >    I need a function: (set-list-elt list old-elt new-elt)
> >
> >    How? translate list to vector, modify, then turn it back???
>
> Try this (not tested):
>
> (defun change-nth (liszt, n, nieuw)
>   (while (> n 0)
>     (setq liszt (cdr liszt)
>           n (1- n)))
>   (if liszt
>      (setcar liszt nieuw)))
(setq aaa '(1 2 3 4 5 b a "ccc"))
(change-nth aaa 3 'BB)
aaa  --> (1 2 3 BB 5 b a "ccc")    , it works, thank you!