Roman Numerals in Clojure

I saw this post on Roman Numerals in Clojure:

http://www.jayway.com/2012/08/04/a-decimal-to-roman-numeral-converter-in-just...

This is the sort of little programming problem that can stop useful work dead in its tracks. Here's my shot at the problem. I think it reads better in that the recursion just deals with the numbers and the Roman numeral strings are mapped latter. It's also a bit more efficient in the way it tests against the Roman "bases" (as I call them). There's no need to retest against a high base once your interim value has gone below that mark. In any case, my version is quite a bit faster than the other solution in my micro-benchmarks.

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(ns miner.roman   (:require [clojure.test :refer :all])) ;; inspired by ;; http://www.jayway.com/2012/08/04/a-decimal-to-roman-numeral-converter-in-just-a-few-lines/ (def roman-map {1000 "M" 900 "CM" 500 "D" 400 "CD"                 100 "C" 90 "XC" 50 "L" 40 "XL"                 10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I"}) (def roman-bases (sort > (keys roman-map))) (defn roman-addends [n]   {:pre [(< 0 n 4000)]}   (loop [n n bases roman-bases addends []]     (if (zero? n)       addends       (let [base (first bases)]         (if (>= n base)           (recur (- n base) bases (conj addends base))           (recur n (rest bases) addends)))))) (defn roman [n]   (apply str (map roman-map (roman-addends n)))) ;; contrib clojure.pprint/cl-format works but is slow (defn roman-cl [n]   (clojure.pprint/cl-format nil "~@R" n)) (deftest roman-4k   (doseq [n (range 1 4000)]     (is (roman-cl n) (roman n))))

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