Hi Mark,

Yes I would favour Rebecca's approach in her book to use Semigroup. Personally I never think of lists as Monads, as I see this instance useful only to power list comprehension. 

Concatenation with (<>) is more meaningful and holds better semantics than (<|>), described as just "An associative binary operation".  It's so vague it could be the documentation for a Magma typeclass, and the name "Alternative" is quite loaded (we think especially of parsers when thinking/seeing Alternative).

Cheers,

Hécate

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 <> .

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