(defun rand-image (pathname m n)

  (with-open-file (p pathname :direction :output :if-exists :rename)

    (format p "P3 ~A ~A 255~%" m n)

    (loop

     for i upfrom 0 below (* m n) do

     (format p "~A ~% ~A ~% ~A ~%" (random 255) (random 255) (random 255)))))