arrow_test.hs

{-# LANGUAGE Arrows #-}

import Control.Arrow

multiply2 :: (Num a) => (->) a a
multiply2 = arr (\x -> x * 2)
multiply4 :: (Num a) => (->) a a
multiply4 = arr (\x -> x * 4)

addA f g = proc x -> do
                y <- f -< x
                z <- g -< x
                returnA -< (y + z)

plus1 :: Int -> Int
plus1 = proc x -> returnA -< (x + 1)

plus3 :: Int -> Int
plus3 = proc x -> returnA -< (x + 3)

plus2 :: Int -> Int
plus2 = proc y -> do x <- plus1 -< y
                     plus1 -< x

comparr :: Int -> Int
comparr = plus1 >>> plus3 >>> plus2

main :: IO()
main = putStrLn $ show $ addA multiply2 multiply4 (5.5 :: Float)