[Haskell-cafe] OpenGL: No instance for Random GLfloat

Hi Haskellers, I'm trying to generate a random vertex in OpenGL as follows. genPosition :: IO (Vertex3 GLfloat) genPosition = do x <- getStdRandom $ randomR (-1.6,1.6) y <- getStdRandom $ randomR (-1.0,1.0) return (Vertex3 x y (-1)) Unfortunately the compiler complains about me having to implement an instance of Random for GLfloat. How do I do this (or avoid having to do this)? Cheers, Mark