#| A simple recursive program to calculate the factorial of a number |#


(format t "~%To run the factioral program: (factorial 5)~%")

(defun factorial (x)
  (if (eql x 0)
    1				; If x = 0, then return 1. BASE CASE
    (* x (factorial (- x 1)))))	; Otherwise return x times the factorial of-1. RECURSIVE CASE


#| Output:

CL-USER(26): (factorial 5)
120

CL-USER(27): (factorial 50)
30414093201713378043612608166064768844377641568960512000000000000


|#