Re: [Caml-list] GADT memory representation

[Dmitry Bely <dmitry.bely@gmail.com>]

On Thu, Dec 1, 2016 at 12:52 PM, David Allsopp <dra-news@metastack.com> wrote:
> Dmitry Bely wrote:
>> I need to access/modify GADT data from C glue code. What is their memory
>> representation? Is there any difference from ordinary sum types?
>
> It's the same - GADTs are "just" add a lot of clever typing stuff on top of a normal sum type - they don't affect the runtime operation of the code.

Thanks a lot for your explanation. Let me ask another dumb question
regarding GADTs. What should I do to make the following code
typecheck?

type sum = Int_ of int | Float_ of float;;
type _ gadt = Int : int -> int gadt | Float : float -> float gadt;;
let convert (type el) v : el gadt = match v with  Int_ i -> Int i |
Float_ f -> Float f;;

Characters 61-66:
   let convert (type el) v : el gadt = match v with  Int_ i -> Int i |
Float_ f -> Float f;;
                                                               ^^^^^
Error: This expression has type int gadt
       but an expression was expected of type el gadt
       Type int is not compatible with type el

>> Unfortunately OCaml manual doesn't even mention GADTs in section
>> "Interfacing C with OCaml".
>
> That's worth a GPR/Mantis issue.

Yes, I'll submit one.

- Dmitry Bely