Remove WrappedMonad

[Dan Burton]

I don't quite understand the comment about DerivingVia.

If Monad keeps return as a typeclass method, then DerivingVia could be used
> to produce an Applicative instance from a Monad instance.


Why would DerivingVia be needed for this? If you have your hands on a Monad
instance, then you always have access to the corresponding Applicative
instance, since Applicative is a superclass of Monad. I'm not sure how
DerivingVia comes into play here, or how the "monad of no return" proposal
would change anything about this. Can someone spell it out for me?

-- Dan Burton

On Wed, Apr 25, 2018 at 6:11 PM, Andrew Martin <andrew.thaddeus at gmail.com>
wrote:

> Control.Applicative features a type named WrappedMonad that is used to
> recover an Applicative instance from a Monad instance. However, since GHC
> 7.10, it hasn't been possible to write an Monad instance without an
> Applicative instance. Consequently, this type is useless (with one caveat
> below). I propose removing this type.
>
> Trac Ticket: https://ghc.haskell.org/trac/ghc/ticket/15027
> GitHub PR: https://github.com/ghc/ghc/pull/129
>
> On the PR, David Feuer suggests that the type may have some utility
> depending on whether the monad-of-no-return proposal is accepted (and also
> on whether DerivingVia is accepted, but this one seems more sure). If Monad
> keeps return as a typeclass method, then DerivingVia could be used to
> produce an Applicative instance from a Monad instance. If anyone knows the
> status of this proposal, that could be helpful. This aside, all indication
> of approval or disapproval of this proposal are welcome. Also, I'd really
> love to know if anyone is even using this type.
>
> --
> -Andrew Thaddeus Martin
>
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