put error printing in place

src/Main.hs

@@ -135,6 +135,8 @@ main = do
 
   sp <- createShaderProgram vertSrc fragSrc
   GL.currentProgram $= Just sp
+  err <- get GL.errors
+  print $ "pre-loop errors: " <> show err
 
   -- -- EVENTING AND DRAWING
 
@@ -159,7 +161,10 @@ main = do
       GL.clear [GL.ColorBuffer]
       
       -- the actual drawing happens here
+      void $ get GL.errors
       GL.drawElements GL.Triangles 6 GL.UnsignedInt nullPtr
+      err <- get GL.errors
+      when (not $ null err) (print $ "loop errors: " <> show err)
 
       -- make GL finish things up
       -- GL.flush