I’ve written the following function (using the these library):

import Control.Applicative (Alternative ((<|>)), optional)
import Data.These (These(..))

asumThese :: (Alternative f, Monad f) => f a -> f b -> f (These a b)
asumThese x y = optional x >>= case
  Just x' -> maybe (This x') (These x') <$> optional y
  Nothing -> That <$> y

Is there a way I can remove the Monad constraint, or is there no way out of using bind?

My gut feeling says I can’t avoid the Monad constraint here, but can anyone give me an intuition of why that is the case? Just so in the future I have a better sense of what sort of functions I likely need Monad and which ones I can generalise to Applicative and/or Alternative?

I sense it has something to do with needing Monad for sequencing, but I can’t quite put my finger on it, because f <$> x <*> y parses things in a different sequence to f <$> y <*> x, so there’s still sequencing in Applicative.