The IORef method is the technique I used to solve this same problem, but I'd be interested to see if there was a nice solution involving the state monad. On Mon, Nov 8, 2010 at 8:07 PM, Tom Hobbs wrote:

In case anyone else happens across this and wonders the same as me.  I got this working by using IORef.  Like so;

main = do    world <- sequence (take (worldSize * worldSize) $ repeat rand)    worldM <- newIORef world    -- snip more code   displayCallback $= (display worldM)    idleCallback $= Just (evolveM worldM)    -- snip yet more code

evolveM ior_world = do    world <- readIORef ior_world    let evolved = evolve world    writeIORef ior_world evolved    postRedisplay Nothing

Here, every time the idleCallback is called the world is evolved. Since the displayCallback also has a reference (is that an acceptable term?) to (IORef world) it can draw the latest evolved world.

On Fri, Nov 5, 2010 at 3:55 PM, Tom Hobbs wrote:

...

Hi all,

I have a program which implements Conway's Game Of Life.  It even has an open GL UI which shockingly works.

I've followed a tutorial (http://blog.mikael.johanssons.org/archive/2006/09/opengl-programming-in-hask...) which tells how to get the open GL to animate, and according to my sysouts, that's working to.  The problem I have comes with the fact that between every frame I want to evolve my world but I'm really struggling working out how to get the state stuff working.

Here's a snippet of my main function;

main = do        world <- sequence (take (worldSize * worldSize) $ repeat rand) -- randomly generate a square world        -- code snipped out        displayCallback $= (display position world)  -- display method which is called on every frame redraw        mainLoop

Here, world is a [Int] and represents my cells.  The display function as referenced by "displayCallback" is the function that is called back to everytime the frame is redrawn.

I also have another function which takes in a world, updates the state of the cells and the evolved world, thus;

evolve :: [Int] -> [Int]

I've been reading through (a lot of) tutorials on the state monad but I'm not any closer to working out how I make the call to display take some kind of updated world.

I've also got the following code;

type World = State [Int]

evolveS :: World [Int] evolveS = do              w <- get              let w2 = evolve w              put w2              return w2

Which I believe to be the correct code for wrapping my [Int] in the state monad but now I have two problems;

1) I don't know if it's correct 2) I don't know how to apply it, even if it is

Can anyone offer any advice?

Many thanks,

Tom

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