Nathan Hüsken
When writing games in other (imperative) languages, I like to separate the game logic from the rendering. For this I use something similar to the observer pattern.
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So I am wondering: Is there (or can someone think of) a different pattern by which this could be archived? Or asked different: How would you do it?
That really depends on the FRP framework you are using. A framework can be as simple as to model only the behaviors and events like the original Fran, in which case often a design pattern such as the observer pattern is not even available. One way out of this dilemma is that the main behavior actually gives enough information to draw the scene. In more versatile frameworks, which includes basically any modern framework like Elerea, Netwire and reactive-banana, typically you would model your entire application including the rendering as part of the main behavior. In Netwire you can go as far as having something like this: myApp :: WireM IO a () However, I do not recommend this. As far as possible you should use a stateless monad, ideally simply Identity or a reader: type MyWire = WireM ((->) AppConfig) myApp :: MyWire a GameFrame This is only the first part of the story. The second part is the rendering itself. You certainly want a way to make use of various OpenGL extensions like vertex buffers, which are inherently stateful. One sensible way I see is not to output the game's state, but rather a state delta: myApp :: MyWire a GameDelta That way you can do the imperative stateful plumbing outside of the application's wire and get the full power of FRP without giving up efficient rendering. GameDelta itself would essentially be a type for game state commands. In fact it could be a (free) monad: myApp :: MyWire a (GameDelta ()) someDelta :: GameDelta () someDelta = do randomPos <- liftA2 (,) getRandom getRandom replicateM_ 4 (addCreature randomPos) getPlayerPos >>= centerCamOver Then you could perform that monadic action as part of the rendering process. Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.