Something

(define (icons_destroy int ilst)
  (cond
    [(iempty? ilst)
     (make-ilist_ADT int ilst 1)]
    [else (define len (add1 (ilist_ADT-counter ilst)))
          (set! ilst (make-ilist_ADT int ilst len))
          ilst]))


(define (irest_destroy ilst)
  (set! ilst (ilist_ADT-rest ilst))
  ilst)

(define (icopy il) 
  (define newilist (make-ilist_ADT (ilist_ADT-first il)
                                   (ilist_ADT-rest il)
                                   (ilist_ADT-counter il)))
  newilist)