I am trying to figure out how to use GHC's arrow commands, and I found some extremely weird behavior. In GHC's manual, there is a description of arrow commands, which I don't really understand. http://www.haskell.org/ghc/docs/latest/html/users_guide/arrow-notation.html#... (Primitive Constructs) I have two questions: 1. What are arrow commands supposed to do? 2. What is this code supposed to do? -- start of code -- {-# LANGUAGE Arrows #-} module Main where import Control.Arrow foo :: (b -> String) -> ((((b, Int), Float), Double) -> String) -> (b -> String) foo f g b = f b ++ " " ++ g (((b, 8), 1.0), 6.0) bar :: (t -> String) -> ((Double, Int) -> String) -> t -> String bar f g = proc x -> do (f -< x) `foo` \n m -> g -< (n) main = do putStrLn $ foo show show 17 putStrLn $ bar show show 17 putStrLn $ foo show show 42 putStrLn $ bar show show 42 -- end of code -- Output from GHCi: 17 (((17,8),1.0),6.0) 17 (6.730326920298707e-306,0) 42 (((42,8),1.0),6.0) 42 (6.730326920298707e-306,0) Output after compiling with GHC: 17 (((17,8),1.0),6.0) 17 (5.858736684536801e-270,0) 42 (((42,8),1.0),6.0) 42 (5.858736684536801e-270,0) GHC Version: The Glorious Glasgow Haskell Compilation System, version 6.12.3 Thank you -- Ron