bbrown wrote:
This is more an aesthetics question, I have a simple opengl application that has a singleton like object I need to pass around to the display loop and possibly to the keyboard action handler. (pseudo code)
data SimpleMech = SimpleMech { mechPos :: !MVector, mechRot :: !MVector } deriving (Read)
mainMech = initMech (0, 0, 0) (0, 0, 0) mainMechRef <- newIORef(mainMech)
displayCallback $= displayGameLoop mainMechRef
rotateMech :: (Double, SimpleMech) -> SimpleMech rotateMech (angle, mech) = -- Calculate a new rotation let (xrot,yrot,zrot) = (mechRot mech) newyrot = newyrot + angle
^^^ That should be newyrot = yrot + angle
in SimpleMech { mechRot = (xrot, newyrot, zrot), mechPos = (mechPos mech) }
displayGameLoop mechRef = do mech <- get mechRef mechRef $= (rotateMech (0.1, mech))
.... .... For some reason in that code above, the "mechRef" doesnt update the value I want to change. It is like I am getting an instance of the initial valyue back. Also, when I use writeIORef, eg writeIORef mechRef (rotateMech (0.1, mech)
I get stack overflow exceptions.
The bug above is probably responsible for both the stack overflows with writeIORef and for a $= that doesn't update (it wants to update, but the program is trapped in an infinite loop). Btw, you don't need parenthesis about function applications, you can use record update syntax and functions with several arguments are usually written in curried form: -- Calculate a new rotation rotateMech :: Double -> SimpleMech -> SimpleMech rotateMech angle mech = mech { mechRot = (xrot, yrot + angle, zrot) } where (xrot,yrot,zrot) = mechRot mech mainMech = initMech (0, 0, 0) (0, 0, 0) main = do mainMechRef <- newIORef mainMech displayCallback $= displayGameLoop mainMechRef displayGameLoop mechRef = do mech <- get mechRef mechRef $= rotateMech 0.1 mech The latter can also be written as displayGameLoop mechRef = do mechRef $~ rotateMech 0.1 Regards, apfelmus