Reader + IO monad transformer

DbIO.hs

import Control.Monad.Reader

data Db = Db { conn :: String }
type DbIO = ReaderT Db IO

insert :: String -> DbIO ()
insert s = do
  conn <- asks conn
  liftIO $ putStrLn ("Using connection " ++ conn ++ " inserting " ++ s)
  
run :: DbIO ()
run = do
  conn <- asks conn
  liftIO $ putStrLn ("Using connection " ++ conn)
  insert "foo"
  return ()

dbContext = 
  Db "this is my cnxn"

main :: IO ()
main = do
  (runReaderT run dbContext)