Hello World of Yampa, Haskell's FRP library.

TryYamp2.hs

{-# LANGUAGE Arrows #-}

import qualified FRP.Yampa as Y

type Inp = (String, String)
type Out = String

main = do
  rh <- Y.reactInit initIO act sf
  loop rh

loop :: Y.ReactHandle Inp Out -> IO ()
loop rh = do
  i <- initIO
  flag <- Y.react rh (1, Just i)
  loop rh

initIO :: IO Inp
initIO = do
  cont1 <- readFile "./file1.txt"
  cont2 <- readFile "./file2.txt"
  return (cont1, cont2)

act :: Y.ReactHandle Inp Out -> Bool -> Out -> IO Bool
act rh ch out = do
  putStrLn ("out:" ++ show out)
  putStrLn "--------------------"
  return False

sf :: Y.SF Inp Out
sf = proc i -> do
  out <- Y.arr (\(s1, s2) -> chomp s1 ++ chomp s2) -< i
  t <- Y.time -< ()
  Y.returnA -< out ++ "--" ++ show t

chomp :: String -> String
chomp = filter (\c -> c /= '\n')

TryYampa.hs

{-# LANGUAGE Arrows #-}

import FRP.Yampa

main = reactimate initial input actuation sf

initial :: IO (String, String)
initial = do cont1 <- readFile "./file1.txt"
             cont2 <- readFile "./file2.txt"
             return (cont1, cont2)

input :: Bool -> IO (DTime, Maybe (String, String))
input bl = do i <- initial
              return (1, Just i)

actuation :: Bool -> String -> IO Bool
actuation ch out = do putStrLn out
                      return False

sf :: SF (String, String) String
sf = proc i -> do
  out <- arr (\(s1, s2) -> chomp s1 ++ chomp s2) -< i
  t <- time -< ()
  returnA -< out ++ "--" ++ show t

chomp :: String -> String
chomp = filter (\c -> c /= '\n')