Add flipped fmap

[Bas van Dijk]

On Wed, Apr 7, 2010 at 3:58 PM, Felipe Lessa <felipe.lessa at gmail.com> 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)

Thanks for the excellent discussion so far,

Bas