Roman numerals

roman.clj

(ns roman.core)

(defmacro defpairs
  "Helper macro to make ordered defs for pairs nicer."
  [varname pairs]
  `(def ~varname
     (partition 2 ~pairs)))

(defpairs digits
  ["M" 1000
   "D" 500
   "C" 100
   "L" 50
   "X" 10
   "V" 5
   "I" 1])

(defn numerals
  "Convert integer n to roman numerals."
  [n]
  (loop [n n, acc ""]
    (if (zero? n)
      acc
      (let [[s v] (some #(if (<= (second %) n) %)
                        digits)]
        (recur (- n v) (str acc s))))))