Re: [Haskell-cafe] Polykinded promoted types

On Dec 10, 2014, at 12:31 PM, Gautier DI FOLCO wrote:

2014-12-10 16:21 GMT+01:00 Richard Eisenberg : The problem I see here is that your List1 and List2 kinds are essentially untyped. These lists are allowed to store any types. For example, I can say `Cons1 'True (Cons1 Int Nil1)`, even though 'True and Int have different kinds. Your List3 won't allow such a construction. You're right that the kinds aren't isomorphic.

Does this help?

Yes, it does. I guess that there is no way to escape ?

Escape what, exactly? I'm not sure what your end goal is, so I don't know what you're trying to escape from. Is this what you want?

data List where Nil :: List Cons :: a -> b -> List

type Foo = Cons True (Cons "x" (Cons () Nil))

That works, but isn't very useful in practice, I don't think... Richard