Re: Add flipped fmap

On Wed, Apr 7, 2010 at 4:12 PM, Bas van Dijk wrote:

On Wed, Apr 7, 2010 at 3:58 PM, Felipe Lessa wrote:

...

Simmetry, as the ticket says.

Indeed, I would like to emphasize that my main reason for adding a flipped fmap is symmetry. I find it hard to explain why <$$> shouldn't be in this list:

(<$>)  ∷ Functor f ⇒ (α → β) → (f α → f β) (<$$>) ∷ Functor f ⇒ f α → (α → β) → f β

(<*>)  ∷ Applicative f ⇒ f (α → β) → (f α → f β) (<**>) ∷ Applicative f ⇒ f α → f (α → β) → f β

(>>=)  ∷ Monad f ⇒ f α → (α → f β) → f β (=<<)  ∷ Monad f ⇒ (α → f β) → (f α → f β)

I think the argument I would make is that (<**>) and (=<<) shouldn't have been added in the first place. Now, it might not be feasible to remove them but should we really add flipped versions of everything because these exists. I understand the Functor feels "close" to Applicative and Monad somehow but you could make the argument that any non-commutative operator should now have a flipped versions and there are more operators than those you listed above.

Thanks for the excellent discussion so far,

Thank you! -- Johan