[Haskell-cafe] Polykinded promoted types

[Richard Eisenberg]

While it's true that Maybe's kind is (* -> *), there still may be a better answer to your question, which asks, "Is there a way to get a polykinded promoted type?" Maybe isn't polykinded, but it's also not promoted. With

data Proxy a = P

we get (Proxy :: k -> *). But that's not promoted either. On the other hand we have ('Just :: k -> Maybe k), which is promoted and polykinded, but maybe not what you want.

Does this help?

Richard

On Dec 8, 2014, at 5:52 PM, Gautier DI FOLCO <gautier.difolco at gmail.com> wrote:

> Hi all,
> 
> Is there a way to get a Polykinded promoted type.
> For example with Maybe I get:
> data Maybe a = Just a | Nothing
> Prelude> :k Maybe
> Maybe :: * -> *
> 
> Is it possible to get a k -> *? If so, how can I do that?
> 
> Thanks in advance for your help,
> Regards.
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