; getAt(list index)
;
; returns the element in the list at the given index by
; recursively cutting the list and decrementing the index
; until it is zero
;
; ex.
;     getAt ( '(1 3 6) 0 )   returns  1
;     getAt ( '(1 3 6) 1 )   returns  3
;
(defun getAt (list index)
    (cond
        ((= index 0) (car list))
        (t (getAt (cdr list) (- index 1)))
    )
)

; insert(pre item post)
;
; inserts an item into a list recursively, given a list
; list that is assumed to precede the given item--post
; is assumed to be the rest of the list
;
; it is assumed that the new item is supposed to go
; either between pre and post, somewhere in post,
; or after post
;
(defun insert (pre item post)
    (cond
        ; if post is null, then we've reached the end
        ; of the list, and we need to add item to the end
        ((null post) (append pre (list item)))

        ; if the next item in post precedes item in
        ; order, then recursively call insert, with
        ; the next item in post removed and added to
        ; pre
        ((> (car post) item)
            (insert (append pre (list (car post)))
                    item
                    (cdr post)
            )
        )

        ; otherwise, we know that the item belongs
        ; right here between pre and post
        (t (append (append pre (list item)) post))
    )
)

; insertstr (pre item post)
;
; same as insert() except for strings
;
; uses "string<" instead of just "<"
;
(defun insertstr (pre item post)
    (cond
        ((null post) (append pre (list item)))
        ((string> (car post) item) 
            (insert (append pre (list (car post)))
                    item
                    (cdr post)
            )
        )
        (t (append (append pre (list item)) post))
    )
)

; addToList (item list)
;
; adds a new item to list in descending order
;
; it is assumed that the items in list
; are already sorted in descending order
;
(defun addToList (item list)
    (insert '() item list)
)

; addStrToList (item list)
;
; same as addToList() except for strings
;
(defun addStrToList (item list)
    (insert '() item list)
)

Screen capture of run of addToLis
>
(addToList 1 '())
(1)
> (addToList 1 '(2))
(2 1)
> (addToList 1 '(-3))
(1 -3)
> (addToList 5 '(25 15 10))
(25 15 10 5)
> (addToList 5 '(4 3 2 1))
(5 4 3 2 1)
> (addToList 5 '(15 10 0 -5))
(15 10 5 0 -5)
>