applicative initialization

gistfile1.txt

import Control.Monad.Writer hiding (liftIO)
import Data.Functor.Compose

type InitIO = Compose (Writer (IO ())) IO

-- | Do no initialization
liftIO :: IO a -> InitIO a
liftIO = Compose . pure

liftInit :: IO () -> InitIO ()
liftInit act = Compose (return () <$ tell act)

initializeAndRun :: InitIO a -> IO a
initializeAndRun act = case runWriter (getCompose act) of
	(go, init) -> init >> go

open :: String -> InitIO ()
open s
	=  liftInit (putStrLn ("initializing " ++ s))
	*> liftIO (putStrLn ("running " ++ s))

main = initializeAndRun
	$  open "dialog"
	*> open "window"