[Haskell-cafe] Re: Data types, opengl display loop and readIORef/writeIORef

2007-10-08 Thread apfelmus 

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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Re: [Haskell-cafe] Re: Data types, opengl display loop and readIORef/writeIORef

2007-10-08 Thread bbrown 
On Mon, 08 Oct 2007 17:41:12 +0200, apfelmus wrote
 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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That should be 
newyrot = yrot + angle 


Thanks, I can't believe I missed that bug.  I laughed out loud when I saw 
that.

--
Berlin Brown
[berlin dot brown at gmail dot com]
http://botspiritcompany.com/botlist/?

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