Haskell语言学习笔记（47）Arrow（2）

Function, Monad, Arrow

f :: Int -> (Int, Int)
f = \x ->
  let y  = 2 * x
      z1 = y + 3
      z2 = y - 5
  in (z1, z2)

-- ghci> f 10
-- (23, 15)

fM :: Int -> Identity (Int, Int)
fM = \x -> do
  y  <- return (2 * x)
  z1 <- return (y + 3)
  z2 <- return (y - 5)
  return (z1, z2)

-- ghci> runIdentity (fM 10)
-- (23,15)

fA :: Int -> (Int, Int)
fA = proc x -> do
  y  <- (2 *) -< x
  z1 <- (+ 3) -< y
  z2 <- (subtract 5) -< y
  returnA -< (z1, z2)

-- ghci> fA 10
-- (23,15)

24 Days of GHC Extensions: Arrows