We know that lists have map.  Sometimes we want to take the higher perspective of Functor, replacing map with fmap, then replacing fmap with <$> .  This post asks the corresponding question about append.

The notation for append within List itself is ++ .  Often we think of lists as Monads.  Applicative generalizes Monad, and Alternative specializes Applicative.  Alternative has <|> which behaves as ++ on List.  I have been using <|> for this purpose.

Recently, I have begun to read and enjoy "Effective Haskell".  In Chapter 1, this book uses <> for append.  Clearly they are thinking of List as a Semigroup.

I'm curious about your thoughts on ++ versus <|> versus <> .