gistfile1.clj

(def charset "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
(def N (count charset))

(defn valueFor [x]
  (.indexOf charset (str x)))

(defn charFor [x]
  (nth charset x))

(defn combiner [o]
  (fn [& chars]
    (charFor (mod (reduce o (map valueFor chars)) N))))

(defn crypto [f]
  (fn [data key]
    (apply str
           (map (combiner f) data (cycle key)))))

(def encrypt (crypto +))
(def decrypt (crypto -))

(println (encrypt "THECAKEISALIE" "GLADOS"))
(println (decrypt "ZSEFOCKTSDZAK" "GLADOS"))