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
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