#lang scheme
(define (sum-of-ints li [sum 0])
  (if [< (length li) 2]
    (+ sum (apply + li))
    (let ([f (first li)]
          [s (second li)])
      (if [> s f]
        (sum-of-ints (cddr li) (+ sum (- s f)))
        (sum-of-ints (cdr  li) (+ sum f))))))

(define roman-to-dec '())
(set! roman-to-dec
  (let ([rtoa #hash((#\M . 1000) 
                    (#\D . 500) 
                    (#\C . 100) 
                    (#\L . 50) 
                    (#\X . 10) 
                    (#\V . 5) 
                    (#\I . 1))])
    (lambda (roman)
      (sum-of-ints 
        (map 
          (lambda (x) (hash-ref rtoa x)) 
          (string->list (string-upcase roman)))))))

(define test-data '("XLII" "LXIX" "mi" "MCMLXXXV"))

(for ([r test-data])
  (printf "~a ~a~n" r (roman-to-dec r)))

##</code><code>##

+% mzscheme roman.ss
XLII 42
LXIX 69
mi 1001
MCMLXXXV 1985