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Declaring and working with types in Haskell

I recently played with a Haskell function -XDataKinds

and found that I want to create a view.

I'm not sure if my wishes can come true, but from the constraint package it seems like it is a declared view Constraint

(with a type BOX

) that says it is defined in GHC.Prim

, but I couldn't find it.

Is there a way to manually declare a view in Haskell or GHC? This will probably require manual confirmation that the datatypes declared with data

will have the proper appearance. My idea looks something like this:

data Foo :: BOX

data Bar a :: Foo where
  Bar :: a -> Bar a
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In the current GHC (7.8 at the time of writing) it is not possible to declare a new species from declaring its inhabitants at the type level.



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