> This is a silly example. Console lines "b = x" update the value of b; "c =
> y" likewise; lines starting "a" cause the current value of a to be printed.
>
> module Main
> where
>
> import FRP.Reactive
> import FRP.Reactive.LegacyAdapters
> import Data.List
> import Control.Monad
> import Control.Concurrent
> import Control.Applicative
>
> parseEvent :: String -> Event String -> Event Integer
> parseEvent s = fmap read . joinMaybes . fmap (stripPrefix s)
>
> main :: IO ()
> main = do
> cl <- makeClock
> (s,e) <- makeEvent cl
> forkIO . forever $ getLine >>= s
> let b = stepper 0 $ parseEvent "b =" e
> let c = stepper 0 $ parseEvent "c =" e
> let p = parseEvent "a" e
> let a = liftA2 (+) b c -- the only interesting line
>
> adaptE . fmap print $ snapshot_ a p
>
> So yes, this does use explicit concurrency because "feeding" the reactive
> events (with getLine) and printing the answers must happen in different
> threads.
>
> Interestingly, this fairly simple program gobbles CPU and RAM on
> reactive-0.11, as well as running with a bit of a lag. Could joinMaybes be
> to blame? I don't know how happy the Monad instance of Event is these days.
>