Conway's Game of Life in Clojure

core.clj

;;; Conway's Game of Life
;;; Using a set of coordinates to provide a infinite world
;;;
;;; Moritz Ulrich <[email protected]>
;;; Cologne Clojure User Group
;;; November 17, 2011

(ns game-of-life.core
  (:use [clojure.set :as set]))

(defrecord Coord [x y])
(defn coord [x y] (Coord. x y))

(defn neighbors [world c]
  (let [deltas [[1 0]
                [1 1]
                [0 1]
                [-1 0]
                [0 -1]
                [-1 1]
                [1 -1]
                [-1 -1]]]
    (map (fn [[x y]] (make-coord
                      (+ x (:x c)) (+ y (:y c)))) deltas)))

(defn neighbor-count [world c]
  (count (keep #(get world %) (neighbors world c))))

(defn dies? [world c]
  (let [x (neighbor-count world c)]
    (or (< x 2)
        (> x 3))))

(defn survives? [world c]
  (<= 2 (neighbor-count world c) 3))

(defn reborn? [world c]
  (= 3 (neighbor-count world c)))

(defn reborn-helper
  "Returns a set containing all coordinates we need to check for birth"
  [world]
  (reduce set/union (map (partial neighbors world) world)))

(defn next-generation [world]
  (set/union (set (remove (partial dies? world) world))
             (set (filter (partial reborn? world) (reborn-helper world)))))