clear [ColorBuffer]

Hello,

The program:

import Graphics.Rendering.OpenGL
import Graphics.UI.GLUT

main = do
  _ <- getArgsAndInitialize
  createWindow "Hello World"
  displayCallback $= clear [ ColorBuffer ]
  mainLoop

and the problem:
The ColorBuffer is not cleared, the window shows what was there before it was 
created.
Creating windows, drawing points,... works all well, but "clear [ 
ColorBuffer ]" seems not to work.
(I'm using the ghc 6.6 on Windows)

Thanks in advance for your help.