I cannot get Reactive to behave. I am trying to write a simple program that feeds events to a function and prints 'DING!' when it receives an event from the function. If the function is id or (join . return), it works correctly. If the function is (>>= return), it consumes all of my RAM and does nothing. Why? I've spent several days trying to figure this out. I am using GHC 6.12.1 for x86_64 Linux. import FRP.Reactive import FRP.Reactive.Reactive import FRP.Reactive.Internal.Reactive import FRP.Reactive.Internal.Timing import FRP.Reactive.LegacyAdapters import Control.Monad import Control.Concurrent import Control.Applicative runEventProcessor :: (Event () -> Event ()) -> IO () runEventProcessor f = do clk <- makeClock (sink, ev) <- makeEvent clk forkE (wait clk) . fmap (\_ -> putStrLn "DING!") . f $ ev forever $ do getLine -- wait for <ENTER> sink () putStrLn "<< button pressed >>" threadDelay 100000 -- avoid pressing button too fast wait clk = sleepPast (cGetTime clk) . exactNB explodes1 = runEventProcessor (>>= return) explodes2 = runEventProcessor (join . fmap (Event . pure . pure)) works1 = runEventProcessor (join . return) works2 = runEventProcessor (fmap id) works3 = runEventProcessor (join . Event . pure . pure) -- requires joinE to be exported from FRP.Reactive.PrimReactive -- works4 = runEventProcessor (joinE . return)