{-# LANGUAGE DeriveFunctor #-}

module Main where

-- Derive functor for a data type with functions and tuples

data ReaderWriter r w a = RW { runRW :: r -> (a,w) }
    deriving (Functor)

data Cont r a = Cont { runCont :: (a -> r) -> r }
    deriving (Functor)

main = do
    let rw = RW (\r -> ("something",r*3))
    print (runRW rw 123)
    print (runRW (fmap reverse rw) 456)
    let five = Cont ($ 5)
    runCont five print
    runCont (fmap (*2) five) print

data X a = X
instance Functor X where
   fmap _ X = X