anchor.diff:      (let* ((vertex-array (gl:gen-vertex-array))
   	   (buffers (gl:gen-buffers 2))
   	   (vertex-buffer (elt buffers 0))
  -	   (program (link-program)))
  +	   (program (link-program *shader-source* *fragment-source*)))
         (gl:bind-vertex-array vertex-array)
         (gl:bind-buffer :array-buffer vertex-buffer)
         (load-buffer-array #(-1.0 -1.0 0.0
  
positive.code: (require 'cl-opengl) 
  (require 'glop)
  
  (defvar *shader-source* 
  "#version 330 core
  layout(location = 0) in vec3 in_Position;
  void main() {
  
negative.code:   gl_Position.w = 1.0;
  }")
  
  (defparameter *fragment-source*
  "#version 330 core
  out vec3 out_Color;
  void main() {
  