Functions to execute specific moves on the Reversi board

reversi-flip.clj

(defn flip [board piece move direction]
  "Returns a new board with results of playing the specified move and piece"
  (if (flippable? board piece move direction)
    (loop [b board m (vec (map + move direction))] ; bind board to b so we can use it in recur
      (let [r (m 0)
            c (m 1)
            p ((board r) c)]
        (if (= p piece)
          b ; we've come to a piece the same colour as the active piece, so we're done flipping. Return the modified board.
          (recur (assoc b r (assoc (b r) c piece)) (vec (map + m direction)))))) ; more flipping to be done, so flip and recur.
    board)) ; move+piece won't cause a flip, so just return the board

(defn place-piece [board piece move]
  "Returns a new board that results from playing the specified piece and move."
  (if (move-valid? board piece move)
    (let [r (move 0) c (move 1)]
      ((comp
         #(assoc % r (assoc (% r) c piece))
         #(flip % piece move (directions :N ))
         #(flip % piece move (directions :NE ))
         #(flip % piece move (directions :E ))
         #(flip % piece move (directions :SE ))
         #(flip % piece move (directions :S ))
         #(flip % piece move (directions :SW ))
         #(flip % piece move (directions :W ))
         #(flip % piece move (directions :NW )))
        board)))) ; the move and piece were not valid, so just return the board unchanged

;; An alternative version of place-piece
(defn place-piece-alt [board piece move]
  "Returns a new board that results from playing the specified piece and move."
  (if (move-valid? board piece move)
    (let [r (move 0) c (move 1) b (atom board)]
      (swap! b #(assoc % r (assoc (% r) c piece)))
      (swap! b #(flip % piece move (directions :N )))
      (swap! b #(flip % piece move (directions :NE )))
      (swap! b #(flip % piece move (directions :E )))
      (swap! b #(flip % piece move (directions :SE )))
      (swap! b #(flip % piece move (directions :S )))
      (swap! b #(flip % piece move (directions :SW )))
      (swap! b #(flip % piece move (directions :W )))
      (swap! b #(flip % piece move (directions :NW ))))
    board))