Budapest Clojure Meetup Coding Dojo

num-to-roman.clj

(ns roman-nums.core
  (:require
   [clojure.test :refer [is testing]]))

(def roman-digits [[1000  "M"]
                    [500  "D"]
                    [400 "CD"]
                    [100  "C"]
                    [50   "L"]
                    [40  "XL"]
                    [10   "X"]
                    [5    "V"]
                    [4   "IV"]
                    [1    "I"]])

(defn num-to-roman
  "Convert a number to roman"
  [n]
  (if (pos? n)
    (let [[value romnum] (first (filter #(>= n (first %)) roman-digits))]
      (str romnum (num-to-roman (- n value))))
    ""
    )
  )

(testing "roman for 0"
  (is (= (num-to-roman 0) ""))
  )

(testing "roman for 1"
  (is (= (num-to-roman 1) "I"))
  )

(testing "roman for 3"
  (is (= (num-to-roman 3) "III"))
  )

(testing "roman for 4"
  (is (= (num-to-roman 4) "IV"))
  )

(testing "roman for 41"
  (is (= (num-to-roman 41) "XLI"))
  )

(testing "roman for 971"
  (is (= (num-to-roman 971) "DCDLXXI"))
  )

your last example, 971 seems wrong to me.

Yes should be CMLXXI, as for 91 is XCI and 9 is IX.