world_step   xtlang

(bind-func world_step
  (lambda (w)
    (letz ((cv 0)
           (n 0)
           (pending_updates:List* null))
      (doloop (i (world_height w))
        (doloop (j (world_width w))
          (set! cv (cell_value w i j))
          (set! n (cell_count_neighbors w i j))
          (if (= cv 0:i8)
              ;; birth
              (if (= n 3:i8)
                  (set! pending_updates (cons (CellUpdate i j 1) pending_updates)))
              ;; cell is dead
              (if (not (or (= n 2:i8)
                           (= n 3:i8)))
                  (set! pending_updates (cons (CellUpdate i j 0) pending_updates))))))
      ;; do all the updates
      (for-each (lambda (cu)
                  ;; (println "performing update: x =" (tref cu 0)
                  ;;          "y =" (tref cu 1)
                  ;;          "newvalue =" (tref cu 2))
                  (cell_set_value w (tref cu 0) (tref cu 1) (tref cu 2)))
                pending_updates)
      (world_increment_generation w))))