MVarTransformer.hs

import           Control.Monad.IO.Class (MonadIO)
import           Control.Monad.IO.Class (liftIO)
import           PureMVar

asyncGreet :: (MonadIO m) => MVarT m String
asyncGreet = do
  v <- newMVar
  fork $ do
    let greeting = "Hello world"
    liftIO $ putStrLn greeting
    putMVar v greeting
  takeMVar v