On Tue, Feb 19, 2013 at 9:28 PM, Anton Kholomiov <anton.kholomiov@gmail.com> wrote:

Do you think the approach can be extended for non-regular (nested) algebraic types (where the recursive data type is sometimes at a different type instance)? For instance, it's very handy to use GADTs to capture embedded language types in host language (Haskell) types, which leads to non-regularity.

I'm not sure I understand the case you are talking about. Can you write a simple example
of the types like this?

Here's an example of a type-embedded DSEL, represented as a GADT:

> data E :: * -> * where
>   Lit :: Show a => a -> E a
>   Op :: Op a -> E a
>   App :: E (a -> b) -> E a -> E b
>   ...
>
> data Op :: * -> * where
>   Add :: Num a => E (a -> a -> a)
>   Mul :: Num a => E (a -> a -> a)
>   Neg :: Num a => E (a -> a)
>   ...

-- Conal