Re: Add a Functor instance to Kleisli

Lovely On Thu, Apr 18, 2019 at 12:43 AM Tony Morris wrote:

+1

Including others such as Applicative, Alternative, etc. On 15/4/19 4:34 pm, Fumiaki Kinoshita wrote:

Hello,

This has been proposed as a part of my proposal: https://mail.haskell.org/pipermail/libraries/2019-April/029478.html

2019年4月15日(月) 15:30 Dmitriy Kovanikov :

...

Hello everyone!

I would like to propose to add a `Functor` instance to the `Kleisli` data type from the `Control.Arrow` module. The instance can look like this:

instance Functor m => Functor (Kleisli m a) where fmap :: (b -> c) -> Kleisli m a b -> Kleisli m a c fmap f (Kleisli h) = Kleisli (fmap f . h) {-# INLINE fmap #-}

(<$) :: c -> Kleisli m a b -> Kleisli m a c c <$ Kleisli h = Kleisli (\a -> c <$ h a) {-# INLINE (<$) #-}

Having this instance would be really helpful in improving the `profunctors` package by adding QuantifiedConstraints to it. See more details in the discussion below:

https://github.com/ekmett/profunctors/pull/70#discussion_r267648958

Thanks, Dmitrii Kovanikov

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