(de ant (Width Height X Y)
   (let (Field (make (do Height (link (need Width)))) Dir 0)
      (until (or (le0 X) (le0 Y) (> X Width) (> Y Height))
         (let Cell (nth Field X Y)
            (setq Dir (% (+ (if (car Cell) 1 3) Dir) 4))
            (set Cell (not (car Cell)))
            (case Dir
               (0 (inc 'X))
               (1 (inc 'Y))
               (2 (dec 'X))
               (3 (dec 'Y)) ) ) )
      (prinl "P1")
      (prinl Width " " Height)
      (for Row Field
         (prinl (mapcar '[(X) (if X 1 0)] Row)) ) ) )
(out '(display -) (ant 100 100 50 50))
(bye)