b.txt

;; 2. solution without lexical scope
;;    maintaining global invariants is easy when state is global

;; 10 LOC, 2 vars

(def counters (atom {}))

(defn count [id]
  (swap! counters update id (fnil inc 0)))

(add-watch counters :game-over
  (fn [_ _ _ cs]
    (when-let [top-counter-id (some (fn [[k v]] (when (<= 10 v) k)) cs)]
      (println "Done counting! Top counter:" top-counter-id)
      (reset! counters {}))))

;; Usage example
;; (count :c1)
;; (count :c1)
;; (count :c2)
;; (count :c2)
;; ... etc
;; Done counting! Top counter: :c1