; decimal->roman : integer -> string
; format the integer num using roman numerals
(define (decimal->roman num)
(let ((decimal-numbers (list 1000 900 500 400 100 90 50 40 10 9 5 4 1))
(roman-numbers (list "M" "CM" "D" "CD" "C" "XC" "L"
"XL" "X" "IX" "V" "IV" "I")))
(decimal->roman-aux num "" decimal-numbers roman-numbers)))
; decimal->roman-aux : integer string (list number) (list string) -> string
; append the numbers num formatted as roman numerals to the string s,
; using the roman numerals in roman-numbers with corresponding
; decimal values in decimal-values
(define (decimal->roman-aux num s decimal-numbers roman-numbers)
(if (null? decimal-numbers)
s
(if (>= num (car decimal-numbers))
(decimal->roman-aux (- num (car decimal-numbers))
(string-append s (car roman-numbers))
decimal-numbers roman-numbers)
(decimal->roman-aux num s
(cdr decimal-numbers) (cdr roman-numbers)))))
