(defpackage :fwoar.triangle
   (:use :cl )
   (:export ))
 (in-package :fwoar.triangle)
 
 (defun alternate-source ()
   (let ((alternator t))
     (lambda ()
       (prog1 alternator
         (setf alternator (not alternator))))))
 
 (defun print-triangle (size)
   (let ((alt (alternate-source)))
     (dotimes (n size)
       (let ((count (1+ n)))
         (dotimes (i count)
           (format t "~:[0~;1~] " (funcall alt)))
         (terpri)))))
 
 #|
 TRIANGLE> (print-triangle 11)
 1
 0 1
 0 1 0
 1 0 1 0
 1 0 1 0 1
 0 1 0 1 0 1
 0 1 0 1 0 1 0
 1 0 1 0 1 0 1 0
 1 0 1 0 1 0 1 0 1
 0 1 0 1 0 1 0 1 0 1
 0 1 0 1 0 1 0 1 0 1 0
 |#