transduced game of life

xlife.clj

(ns xlife
  (:require [net.cgrand.xforms :as x]))

;; xforms is a library of transducers

(defn xstep [cells]
  (into #{}
    (comp
      ; a comprenhension to generate neighbours
      (x/for [[x y] % 
              dx [-1 0 1] 
              dy (if (zero? dx) [-1 1] [-1 0 1])] 
        [(+ dx x) (+ dy y)])
      ; reimplementing frequencies as a transducer
      (x/by-key identity x/count)
      ; keeping only alive cells
      (x/for [[cell n] %
              :when (or (= n 3) (and (= n 2) (cells cell)))]
        cell))
    cells))