$ ghci -XDataKinds -XKindSignatures

Prelude> data K = K

Prelude> data Foo (a :: K) = Foo

Prelude> :kind Foo

Foo :: K -> *

Note that types with kinds other than * are uninhabited, so you can't write a version of Maybe with that kind (because the Just constructor would require a value that can't exist).

On Mon, Dec 8, 2014 at 2:52 PM, Gautier DI FOLCO <gautier.difolco@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.

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe