[Haskell-beginners] Is it possible such Monad? (Baa)

[鲍凯文]

Hi,

1. I think your data type is isomorphic to

data Allpass w m a = Pass Bool (m a) w

2. Maybe first try to write a Functor instance? Then you can find out what
constraints are necessary for 'w' and 'm' to write it.

3. What does this data type intend to represent?

Best,

toz

On Wed, Oct 25, 2017 at 5:32 AM <beginners-request at haskell.org> wrote:

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> Message: 1
> Date: Wed, 25 Oct 2017 13:56:31 +0300
> From: Baa <aquagnu at gmail.com>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
>         beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: [Haskell-beginners] Is it possible such Monad?
> Message-ID: <20171025135631.1f9913d2 at Pavel>
> Content-Type: text/plain; charset=US-ASCII
>
> Hello All!
>
> Is it possible to write Monad for such type:
>
>   data Allpass w m a = Nopass (m a) w | Allpass (m a) w
>
> I can write (>>=), IMHO such type can not be Monad due to `w` is not
> under `m` monad, right?
>
>
> ===
> Best regards, Paul
>
>
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