gistfile1.lisp

(defn update-ladder-for-game [{winner :winner loser :loser :as game}]
  (dosync
   (if (empty? @ladder)
     (alter ladder into (vector winner loser))
     (when-first [[_ index] (filter #(= (first %) loser) (map list @ladder (iterate inc 0)))]
                 (let [base1 0
                       stop1 (- index 1)
                       base2 index
                       modvec (-> (subvec @ladder base1 stop1) (conj winner) (into (subvec @ladder base2)))]
                   (alter ladder (fn (& _) modvec)))))))