(defun roman_to_dec (roman)
    (if (not (equal roman ""))
      (let ((rtoa '((#\M . 1000)
                    (#\D . 500)
                    (#\C . 100)
                    (#\L . 50)
                    (#\X . 10)
                    (#\V . 5)
                    (#\I . 1))))
        (reduce #'(lambda (a b) (- (+ a b) (* (mod a b) 2)))
                (map 'list
                     #'(lambda (c) (cdr (assoc c rtoa)))
                     (string-upcase roman))))))