Which is awfully similar to Haskell's Maybe. Ignoring boilerplate and comments, the entire module is just [0]:

  data Maybe a = Nothing | Just a
    deriving ( Eq, Ord )

And the deriving line isn't really nessasary.

The Monad module is larger and contains code specific to Maybe [1]:

  instance  Monad Maybe  where
    (Just x) >>= k      = k x
    Nothing  >>= _      = Nothing
    (>>) = (*>)
    fail _              = Nothing

(Only the first 2 lines are needed. The 3rd is an optimization, the 4th is a historical wart that will be removed in future versions (moved to MonadFail)

[0] https://hackage.haskell.org/package/base-4.12.0.0/docs/src/G...

[1] https://hackage.haskell.org/package/base-4.12.0.0/docs/src/G...