1.- First  we are going to define the function
 
(defun factorial (n)
  "Returns factorial of the number n"
  (if (= n 0)
      1
      (* n (factorial (- n 1)))))

2.- Set trace to function
 
 (trace factorial *)

3.- Call the function

 (factorial 3)
 
4.- Finally we show the results
 
  0: (FACTORIAL 3)
    1: (FACTORIAL 2)
      2: (FACTORIAL 1)
        3: (FACTORIAL 0)
        3: FACTORIAL returned 1
      2: FACTORIAL returned 1
    1: FACTORIAL returned 2
  0: FACTORIAL returned 6
#Lisp