rsp.clj

(def items [:rock :paper :scissors])

(defn winner [m1 m2]
  (mod (- m1 m2 1) 3))

(defn player-string [name symbol]
  (str name (nth items symbol) " wins!"))

(defn player-wins [m1 m2]
  (str (nth items m1) " vs. " (nth items m2) " !! "
    (nth [(player-string "player1" m1)
      (player-string "player2" m2) "tie"] (winner m1 m2))))

(defn indexof-failed [seq val]
  (let [i 0]
    (if (some (fn [cur] 
                (if (= cur val)
                  val
                  (= (inc i) 0)))
        seq)
      i
      nil)))

(defn indexof [seq val]
  (letfn [(find-val [seq val count]
    (cond (= seq ()) nil 
      (= (first seq) val) count
      :else (find-val (rest seq) val (inc count))))]
    (find-val seq val 0)))

(defn play [m1 m2]
  (player-wins (indexof items m1) (indexof items m2)))

(play :rock :paper)