Father and Son Wallet example

import FRP.Elerea.Param
import Control.Monad

{-
This program is an example of functional reactive programming. There are two people a father and a son
they each have an amount of money and initially each of their values is 0 and 10. However , The father always has £10
more than his son. An updater signal keep track and tells when an amount of money has been added or removed from the
amounts of the father and the son. Here is the code written with the FRP library Elerea.
-}

main :: IO ()
main  = do
    smp <- start $ do
        b <- stateful 0 (+)
        d <- transfer 10 (\d b x -> b + 10) b
        g <- input
        gs <- effectful1 (inputCheck) g
        bs <- effectful2 (\b d -> (shout b d)) b d
        return g

    res <- forM [1,0,1,(-1),1,1,0, 6] smp
    return ()

shout :: Int -> Int -> IO ()
shout b d = putStrLn $ "The Boy has £" ++ show b ++ "\n" ++ "The Dad has £" ++ show d ++ "\n"

inputCheck :: Int -> IO ()
inputCheck x
    | x == 6 = return ()
    | x > 0  = putStrLn $ "--Increased by £" ++ show x
    | x < 0  = putStrLn $ "* Decreased by £" ++ show (abs x)
    | x == 0 = putStrLn "..No Change"