Is there an inverse operation to >>= (kinda)

[jaror]

I think you’re looking for <|>. It “fails” at the first Just

Just 1 <|> Just 2 = Just 1

And it skips over Nothing as if it was a success:

Nothing <|> Just 1 = Just 1

It works out if you consistently think about Just as failure and Nothing as success, even in the final result.

See also this post of mine where I use the alternative instance of Maybe in this way:

The ICFP'22 playlist has been published to YouTube

I’m not arguing for manual examples like those presented in the paper. Instead, you should write proper functional code. For example the paper presents a “succinct” locally imperative implementation of findM: def List.findM? (p : α → m Bool) (xs : List α) : m (Option α) := do for x in xs do let b ← p x if b then return some x return none But in Haskell you can write it as an even more succinct composition of more and less common combinators: findM :: Monad m => (a -> m Bool…