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
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