class Monad m where
  return :: a -> m a
  (>>=) :: m a -> (a -> m b) -> m b

hoge uID = do
  fname <- lookup uID firstNameDB
  lname <- lookup uID lastNameDB
  return $ fname ++ lname

foo = do
  tell ["hello, "]
  tell ["world!"]

main = do
  putStr "こんなんだったり"
  replicateM_ 3 $ do
    threadDelay 1000000
    putStr "."
  putStrLn "。"

do
  a <- do
    b <- foo
    bar b
  baz a

do
  b <- foo
  do
    a <- bar b
    baz a