gistfile1.hs

module Main where

import Control.Monad.Writer
import Control.Monad.Reader

rwt :: A Int
rwt = ask >>= \x -> tell ("Got " ++ show x) >> return (x * 2)

type A = ReaderT Int (WriterT String Maybe)

runA :: A a -> Int -> Maybe (a, String)
runA app i = runWriterT (runReaderT app i)

main = do
    let ee = runA rwt 6
    putStrLn $ (show ee)