Solution to 4Clojure #92 - Read Roman Numerals

read_roman_numerals.clj

(fn [roman-str]
  (let [letter-val {\0 0 ;; for padding last tuple
                    \I 1, \V 5, \X 10, \L 50
                    \C 100, \D 500, \M 1000}
        letter-tuple->dec (fn [[l r]]
                            (* (letter-val l)
                               (if (< (letter-val l) (letter-val r))
                                 -1
                                 1)))]
    (->> roman-str
         (partition 2 1 [\0])
         (map letter-tuple->dec)
         (reduce + 0))))