list-set.scm

;;change the [n]-th item of a list [ls] to [new_val]. Return the modified list.
;; ([ls LIST] [n INT] [new_val ANY]) -> LIST
;; eg. (list-set '("a" "b" "c") 1 2) -> ("a" 2 "c")

(define (list-set ls n new_val)
  (list-set-iter '()  ls (modulo n (length ls)) new_val 0)
  )

(define (list-set-iter ls_left  ls_right n new_val counter)
  (if (< counter n)
     (list-set-iter
      (append ls_left (list (car ls_right)))
      (cdr ls_right)
      n
      new_val
      (+ counter 1))
 (append ls_left (list new_val) (cdr ls_right))
    )
   )