On Sun, Jun 5, 2011 at 12:51 PM, KC
<kc1956@gmail.com> wrote:
If new intermediate classes crop up then there would be no point in fixing
class (Applicative m) => Monad m where
since it would have to be changed if new intermediate classes are found.
You might check out a few articles regarding Kleisli arrows [1][2] for possibilities that live between applicative and monad.
Applicative itself is also a little on the strong side. I had to reject Applicative for one model of signal transformers because 'pure' was not a legal constructor, even though 'fmap . const' and '<*>' were okay. And even Functor is too strong if you want effective linearity. I've found Adam Megacz's Generalized Arrows [3] to be a suitable chassis for weaker models.