Can I Do This In Lisp?

(defun my-index (findMe mylist)
  (let ((counter 0) (found 1))
    (dolist (item mylist)
      (cond
        ((eq item findMe) ;this works because 'eq' checks place in memory,
                  ;and as long as 'findMe' was from the original list, this will work.
         (setq found nil)
        (found (incf counter))))
  counter))

(let ((myList '(1 2 3 4 5 6)))
     (setf (nth 4 myList) 101); <----
     myList)

(1 2 3 4 101 6)

(let ((myList '(1 2 3 4 5 6)))
     (setf (nth 4 myList) 101)
     (list myList (position 101 myList)))

((1 2 3 4 101 6) 4)

> (setq numbers (list 1 2 3 4))
(1 2 3 4)
> (position 3 numbers)
2

(define list-position
  (lambda (o l)
    (let loop ((i 0) (l l))
      (if (null? l) #f
          (if (eqv? (car l) o) i
              (loop (+ i 1) (cdr l)))))))

----------------------------------------------------

> (define numbers (list 1 2 3 4))
> (list-position 3 numbers)
2
>

(defun my-attr (list)
  (nth 4 list))

(defun (setf my-attr) (new list)
  (setf (nth 4 list) new))