;;Functions to help test-recursion
(defun recursive-sum (l)
  (if (null l); if l is mt, return 0
    0
    (if (not (numberp (car l))) ;if car of l is not a number, return nil
      nil
      (+ (car l) (recursive-sum (cdr l)))))); return the value of the car + the value of sum on the cdr of l.

(defun counta (lst count)
  (if (null lst)
          count; if l is mt, return the count
	  (if (eql (car lst) 'a); if car of lst is a, call counta with the cdr of the lst, and incf count
	      (counta (cdr lst) (+ count 1))
	      (counta (cdr lst) count))));else, call counta with the cdr of the lst with the same count

;;Chapter 2, Test 6, Pg 16
(deftest test-recursion ()
  (check
    (equal (recursive-sum (list 1 2 3 4 5)) 15);tests recursive sum with a lst of numbers
    (equal (recursive-sum (list `a `b `c)) nil);tests the error checking on recursive sum
    (= 3 (counta (list `a `b `c `d `a `a) 0));added by Jim, counts the number of a's in lst.
))