I like my code to do what it says. You can pretty much do that in Haskell. If you allow me to add a definition first:

    mfilter' :: MonadPlus m => (a -> Bool) -> a -> m a
    mfilter' f = mfilter f . return

Then it's just:

    toUpperCase <=< mfilter' (\x -> length x /= 0) . trim

Which is pretty close. No need to change the language.