tic_tac_toe.cljs

(let [won-subboard (fn [board]
                     (let [all-equal (fn [v] (and (apply = v) (first v)))]
                       (or
                         ; horizontal lines
                         (all-equal (subvec board 0 3))
                         (all-equal (subvec board 3 6))
                         (all-equal (subvec board 6 9))
                         ; vertical lines
                         (all-equal (vals (select-keys board [0 3 6])))
                         (all-equal (vals (select-keys board [1 4 7])))
                         (all-equal (vals (select-keys board [2 5 8])))
                         ; diagonals
                         (all-equal (vals (select-keys board [0 4 8])))
                         (all-equal (vals (select-keys board [2 4 6]))))))
      board-decided? (fn [board] (or (won-subboard board) (not-any? nil? board)))]
  (fn [{:strs [history grid] :as state}]
    (if (empty? history)
      ; I'm first player
      (pr-str [2 2])
      ; otherwise, we need to play in the correct sub-board
      (let [[b sb] (get (last history) "move")
            board-idx (if (board-decided? (grid sb))
                        (->> (range 0 9) (remove (comp board-decided? grid)) rand-nth)
                        sb)
            board (grid board-idx)]
        (pr-str
          [board-idx
           (->> (range 0 9)
                (filter (comp nil? (partial get board)))
                rand-nth)])))))