+1

Including others such as Applicative, Alternative, etc.

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 <kovanikov@gmail.com>:

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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