(defun factorial (n) (if (= n 0) 1 (* n (factorial (- n 1))) ) ) (defun maybe-pos-int (input) (cond ((null input) nil) ((string= input "") nil) ((every #'digit-char-p input) (parse-integer input)) (t nil))) (defparameter num (maybe-pos-int (cadr *posix-argv*))) (cond ((null num) (write-line "Usage: please input a non-negative integer")) (t (print (factorial num))) )
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Note: The solution shown above is the current solution in the Sample Programs repository as of Oct 11 2020 06:48:59. The solution was first committed on Oct 01 2020 17:40:32. As a result, documentation below may be outdated.
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