On Monday, May 13, 2024 at 03:05:48 AM EDT, Hécate via Haskell-Cafe <haskell-cafe@haskell.org> wrote:

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

Le 12/05/2024 à 21:41, Mark McConnell via Haskell-Cafe a écrit :

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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Hécate ✨
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