 Sample image
The task is to demonstrate the creation of a series of vertical pinstripes across the entire width of the display.

 in the first quarter the pinstripes should alternate one pixel white, one pixel black = 1 pixel wide vertical pinestripes
 Quarter of the way down the display, we can switch to a wider 2 pixel wide vertical pinstripe pattern, alternating two pixels white, two pixels black. 
 Half way down the display, we switch to 3 pixels wide, 
 for the lower quarter of the display we use 4 pixels.


c.f. Colour_pinstripe/Display

(let Pbm  # Create PBM of 384 x 288 pixels
   (make
      (for N 4
         (let
            (C 0
               L (make
                  (do (/ 384 N)
                     (do N (link C))
                     (setq C (x| 1 C)) ) ) )
            (do 72 (link L)) ) ) )
   (out '(display)  # Pipe to ImageMagick
      (prinl "P1")
      (prinl (length (car Pbm)) " " (length Pbm))
      (mapc prinl Pbm) ) )