OpenGL Hello Triangle in common lisp

hello-triangle.lisp

(ql:quickload :cl-glfw3)
(ql:quickload :cl-opengl)

(defvar vs-source "#version 330
in vec3 aPos;
void main(){
  gl_Position = vec4(aPos.x,aPos.y,aPos.z, 1.0);
}")

(defvar fs-source "
#version 330
out vec4 FragColor;
void main()
{
  FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
}")

(defvar *VBO* nil)
(defvar *VAO* nil)

(defun create-default-shader ()
  (let ((*vs* nil)
        (*fs* nil)
        (*shader* nil))
    (setf *vs* (gl:create-shader :vertex-shader))
    (gl:shader-source *vs* vs-source)
    (gl:compile-shader *vs*)
    (setf *fs* (gl:create-shader :fragment-shader))
    (gl:shader-source *fs* fs-source)
    (gl:compile-shader *fs*)
    (setf *shader* (gl:create-program))
    (gl:attach-shader *shader* *vs*)
    (gl:attach-shader *shader* *fs*)
    (gl:link-program *shader*)
    (gl:delete-shader *vs*)
    (gl:delete-shader *fs*)
    *shader*))

(defun create-gl-array (data
                        &optional (type :float)
                        &aux (length (length data)))
  (let ((arr (gl:alloc-gl-array :float length)))
    (dotimes (i (length data))
      (setf (gl:glaref arr i) (aref data i)))
    arr))

(glfw:with-init-window (:width width :height height :title "GLFW")
                       
  ;; Send the buffer data to the GPU
                       
  (setf *VBO* (gl:gen-buffer))
  (gl:bind-buffer :array-buffer *VBO*)
  (gl:buffer-data :array-buffer
                  :static-draw
                  (create-gl-array #(-0.5 0.5 0.0
                                     0.0 0.0 0.0
                                     0.5 0.5 0.0)))
                       
  ;; Tell the GPU what the data represents by binding VAO
                       
  (setf *VAO* (gl:gen-vertex-array))
  (gl:bind-vertex-array *VAO*)
  (gl:vertex-attrib-pointer 0 3 :float :false 0 0)
  (gl:enable-vertex-attrib-array 0)
                       
  ;; main window draw loop
                       
  (let ((shader (create-default-shader)))
    (loop until (glfw:window-should-close-p)
          do (gl:clear :color-buffer)
          do (gl:use-program *shader*)
          do (gl:draw-arrays :triangles 0 3)
          do (glfw:swap-buffers)
          do (glfw:poll-events))))