;Chapter 6, Bryan Test 2, Page 114-116

(defun my-length (l)
  (if (null l); if the list is mt, return 0
    0
    (+ 1 (my-length (cdr l))))); adds 1 to the return value of the cdr of the list.
    
(defun my-member (elt l &optional (fn #'equal))
  (if (null l) ;if list is mt, return nil
    nil
    (if (funcall fn (car l) elt) ;if the keys match, return t
      t
      (my-member elt (cdr l) fn)))); if more of the list exists, return the value of self called with the cdr of the list

(defun my-copy-tree (l)
  (if (atom l);if l is a value or nil, return l
    l
    (if (consp l) ;if l is a conscell, return the cons of the of the copied left and right branches.
      (cons (my-copy-tree (car l)) (my-copy-tree (cdr l)))
      nil)));else return nil
      
(defun my-fib (n) ;BAD TO USE b/c its unefficient.
  (if (<= n 1);if n is less than or equal to 1, return n
    n
    (+ (my-fib (- n 1)); else return fib of n - 1 added to fib of n -2
       (my-fib (- n 2)))))
       
(defun my-factorial (n)
  (if (= n 0)
    1
    (* n (my-factorial (- n 1)))))

(deftest test-recursion-adv ()
  (let ((x '(1 (2 3) 4)))
    (check
      (= (my-length (list 1 2 3 4 5 "a" 7 8 9 10 11)) 11)
      (my-member 5 (list 1 2 3 4 5 6 7 8 9 10))
      (not (my-member 5 (list 1 2 3 4 6 7 8 9 10 11)))
      (equal (my-copy-tree x) x)
      (not (eql (my-copy-tree x) x))

      (= (my-fib 20) 6765)
      (= (my-factorial 10) 3628800))))