Kenny Tilton wrote:

> > Hi! I started yesterday programming in lisp and now I've got my first
> > problem... Suppose that I have a list l1 and a list l2: how can I replace
> > the nth element in list l1 with list l2? (The resulting list should be
> > flat) Maybe it should be better modify the structure of l1 than create a
> > brand new list with the features desired...
> >
> > Thanks!!! piercarlo
> >
> > P.S.: I use GCL 2.2.2
>
> Two answers:
>
> (a) (defun nsplice (l1 n l2) ;; this is destructive version
> (when (< -1 n (length l1))
> (let* ((prior (when (plusp n)
> (nthcdr (1- n) l1)))
> (target (or (cdr prior)
> (nthcdr n l1)))
> (remainder (cdr target)))
>
> (when prior
> (rplacd prior l2))
>
> (rplacd (last l2) remainder)
>
> (if prior l1 l2))))

Scheme:

(let ((l1 '(0 1 2 3 4 5 6 7 8))
(l2 '(903 905)))
`(,@(take l1 2) ,@l2 ,@(drop l1 3)))

===>
(0 1 903 905 3 4 5 6 7 8)