From HaskellWikifunctor but less than a monad. See the Haddock docs for <div class="inline-code">
It has turned out that many applications do not require monad functionality but only those of applicative functors. Monads allow you to run actions depending on the outcomes of earlier actions.
do text <- getLine if null text then putStrLn "You refuse to enter something?" else putStrLn ("You entered " ++ text)
This is obviously necessary is some cases, but in other cases it is disadvantageous.