While hacking a bit on Creighton Hogg's Tetris game, I came across something interesting re composability. I have made each tile appear as a taurus, and decided it might be fun if the tauruses span while you played (just for added vomit-worthyness). So I set about changing my tile from a Geometry3 to a Behavior Geometry3. This went well, until it came to getting the spinning tiles to display something based on the game state. The tetris game is a Behavior GameState, where the game state stores the positions of the tiles on the board etc. What I *want* is that I compute the current game state, by looking into the Behavior GameState, get a GameState up, and then apply a function createTetrisGeometry :: GameState -> Behavior Geometry3. This sounds a lot like (>>=) to me, unfortunately there's no Monad instance for Behavior though :(. I've heard from various sources that the Monad instance is problematic for a couple of reasons. I'd love it if we could have a bit of a discussion about why it's problematic, and if it can be fixed. Thanks Bob p.s. It is possible to hack round this problem by making a function createTetrisGeometry :: TimeT -> GameState -> Behavior Geometry3, and then using (uncurry createTetrisGeometry) <$> (time <^(,)^> tetris). The result currently looks something like this... http://www.cs.kent.ac.uk/people/rpg/tatd2/tetris.png