hex.clj

(ns hex.core)

;;
;; Decode hex numbers - kata
;;

(defn decimal-value [n]
  (or
   (get {\0 0 \1 1 \2 2 \3 3 \4 4 \5 5 \6 6 \7 7 \8 8 \9 9 \a 10 \b 11 \c 12 \d 13 \e 14 \f 15} n)
   (throw (Exception. (str "Invalid number: " n)))))

(defn power-of [n]
  (iterate #(* n %) 1M))

(defn to-decimal [hex]
  (->> (seq hex)
       (map decimal-value)
       reverse
       (map #(* %1 %2) (power-of 16))
       (reduce +)))