``` -- | One can easily implement a monadic 'selec...

# arrow-contributors

[pakoito]

-- | One can easily implement a monadic 'selectM' that satisfies the laws,
-- hence any 'Monad' is 'Selective'.
selectM :: Monad f => f (Either a b) -> f (a -> b) -> f b
selectM x y = x >>= \e -> case e of Left  a -> ($a) <$> y -- execute y
                                    Right b -> pure b     -- skip y