gistfile1.clj

(defn add-buildings
  ([world]
     (add-buildings world 0.5))
  ([world prob]
     (let [maxy (dec (count world))
           maxx (dec (count (world 0)))]
       (loop [world world, cury maxy, curx maxx]
         (if (and (zero? curx) (zero? cury))
           world
           (let [new-world (update-in world [cury curx]
                                      (fn [arg]
                                        (if (> (rand) prob)
                                          (make-building 1.0 0.0 {})
                                          arg)))]
             (if (zero? curx)
               (recur new-world (dec cury) maxx)
               (recur new-world cury (dec curx)))))))))