Dear All,

I'm trying to get my hands wet with the reactive library,
but already the simplest example I cooked up is failing
to work properly (and leaks memory, and uses relatively
lots of cpu time).

The problem appears when I try to merge my two events
with `mappend`. One event should exit on pressing ESC,
the other draws colored circles on pressing the left mouse
button. They work correctly separately.

Could somebody explain me what's happening, or
whether I'm making a basic mistake?

The code is below, I hope the formatting survives the
various email systems. I don't know if that matters or
not, but I'm using OS X.

Thanks,
Balazs

module Main where

import Control.Monad
import Data.Monoid

import FRP.Reactive
import FRP.Reactive.GLUT.Adapter

import Graphics.Rendering.OpenGL hiding (normalize)
import Graphics.UI.GLUT hiding (normalize,Char)

import System.Exit

-------------------------------------------------------

nop :: Monad m => m ()
nop = return ()

data Vec2 = Vec2 !Float !Float

(&+) (Vec2 x1 y1) (Vec2 x2 y2) = Vec2 (x1+x2) (y1+y2)

sinCosRadius a r = Vec2 (r * cos a) (r * sin a)

instance Vertex Vec2 where
vertex (Vec2 x y) = vertex (Vertex2 x y)

-------------------------------------------------------

display :: Action -> Action
display action = do
clear [ ColorBuffer , DepthBuffer ]

siz@(Size xs ys) <- get windowSize
matrixMode $= Projection
loadIdentity
let q = fromIntegral xs / fromIntegral ys
      r = 1 / q
if q >= 1
    then ortho 0 1 r 0 (-1) 1
    else ortho 0 q 1 0 (-1) 1
viewport $= ( Position 0 0 , siz )
matrixMode $= Modelview 0
loadIdentity

action
postRedisplay Nothing
swapBuffers

data Col = RR | GG | BB

nextCol RR = GG
nextCol GG = BB
nextCol BB = RR

setCol RR = color (Color3 1 0 (0::Float))
setCol GG = color (Color3 0 1 (0::Float))
setCol BB = color (Color3 0 0 (1::Float))

drawWithCol col = do
setCol col
let center = Vec2 0.25 0.25
      radius = 0.1
      n = 32
renderPrimitive TriangleFan $ do
    vertex center
    let phi j = 2*pi * fromIntegral j / fromIntegral n
    forM_ [0..n] $ \i ->
      vertex (center &+ sinCosRadius (phi i) radius)

myUI :: UI -> Behaviour Action
myUI ui = uiB where

mp = mousePosition ui
lb = leftButtonPressed ui
rb = leftButtonPressed ui
ky = keyPressed ui

colE = mealy_ RR nextCol lb
drawE = fmap drawWithCol colE

exitE = justE (fmap esc ky) where
    esc k = case k of
      Char '\ESC' -> Just exitSuccess
      _           -> Nothing

uiE = fmap display drawE `mappend` exitE
uiB = stepper nop uiE

-------------------------------------------------------

main = do
initialize "alma" []
initialWindowSize $= Size 512 384
initialDisplayMode $= [ RGBAMode , WithDepthBuffer , DoubleBuffered ]
createWindow "reactive test"
adapt myUI