gistfile1.hs

data Sound
    = Silence
    | Audio AudioData
    | Volume Double Sound
    | Sequence Sound Sound

data SoundM a = SoundM Sound a

instance Monad SoundM where
    return a = SoundM Silence a
    SoundM s a >>= f = let SoundM s' a' = f a in SoundM (Sequence s s') a'

play :: SoundM a -> IO a
play (SoundM s a) = do
    p <- setup
    ...
    close p
    return a


sound :: Sound -> SoundM ()
sound s = SoundM s ()

main = do
    x <- obtain audio data ...
    y <- obtain audio data ...
    play $ do
        sound (Audio x)
        sound (Volume 0.90 (Audio y))