# Talk:Functor hierarchy proposal

Um, it would be good if it was something like:

class (Idiom f) => Monad f where fmap f m = m >>= return . f -- or ap . return ? ap mf mv = mf >>= \f -> mv >>= \v -> return $ f v (>>=) :: f a -> (a -> f b) -> f b

Or am I missing the point?

Serhei 15:24, 29 January 2006 (UTC)

- You can't put defaults for one class in another. Though that could be another proposal. —Ashley Y 21:02, 29 January 2006 (UTC)

- Wasn't this part of John Meacham's class system proposal? What happend to this? -- Wolfgang Jeltsch 19:25, 2 February 2006 (UTC)

`<*>`

should really be merged with `ap`

, right ?
(Btw, why such a symmetric operator symbol as `<*>`

? `<*`

or some other assymetric one would be better .. even plain ``ap``

is not so bad, imho.)

Also, it would be nice to change `sequence`

, `sequence_`

, `mapM`

and `mapM_`

to only require `Applicative`

instead of `Monad`

. (Or one could merge these four into something like `Data.FunctorM.FunctorM`

, which should use `Applicative`

anyway.) -- StefanLjungstrand 10:18, 3 November 2006 (UTC)

I think it makes sense to take return out of Applicative. Either into a separate step between Functor and Applicative, or into a new class altogether:

```
class Boxable f where
return :: a -> f a
class (Functor f, Boxable f) => Applicative f where
...
```

But maybe this is just overengineering.

Twanvl 21:46, 15 January 2007 (UTC)