To do an IO action with the resulting value of a Monad we can either unwrap the Monad or use a Monad Transformer

monad_transformer.hs

import Control.Monad.Trans (lift)
import Control.Monad.Trans.Maybe (MaybeT, runMaybeT)

monadicAdd :: Monad m => m Int -> m Int -> m Int
monadicAdd l r = do
  l_ <- l
  r_ <- r
  return (l_ + r_)

printWithTransformerMonad :: MaybeT IO Int -> MaybeT IO Int
printWithTransformerMonad n = do
  n_ <- n
  lift . print $ n_

  return n_

main :: IO ()
main = do
  let x = return 1
  let y = return 2

  let r = monadicAdd x y

  runMaybeT $ printWithTransformerMonad r

  return ()

monad_transformer.sh

runghc monad_transformer.hs
#=> 3

unwrap_monad.hs

monadicAdd :: Monad m => m Int -> m Int -> m Int
monadicAdd l r = do
  l_ <- l
  r_ <- r
  return (l_ + r_)

main :: IO ()
main = do
  let x = return 1
  let y = return 2

  -- Be careful, we will get a runtime error if monadicAdd returns Nothing
  let Just r = monadicAdd x y

  print r

unwrap_monad.sh

runghc unwrap_monad.hs
#=> 3