Defining a type and a module type recursively

Defining a type and a module type recursively

[Daniel Bünzli]

Hello,

I have now side stepped the issue but I wonder. Is it possible to
define a type and a module type recursively ?

E.g., something like

type 'a t = 'a * (module T)
and module type T = sig ... (* mentions 'a t somewhere *) ... end

Thanks,

Daniel

Re: [Caml-list] Defining a type and a module type recursively

[Kaustuv Chaudhuri]

On Sat, Aug 28, 2010 at 10:30 AM, Daniel Bünzli
<daniel.buenzli@erratique.ch> wrote:
> Is it possible to define a type and a module type recursively ?

Technically, you can use recusive modules to encode all kinds of
recursive type definitions. Here, for example, is your case:

    module rec M : sig
      type 'a t = 'a * (module N.T)
    end = struct
      type 'a t = 'a * (module N.T)
    end

    and N : sig
      module type T = sig
        type s = S of int M.t
      end
    end = struct
      module type T = sig
        type s = S of int M.t
      end
    end

    type 'a t = 'a M.t
    module type T = N.T

It's pretty ugly. Please only use such patterns if you have solid
reasons not to go with something simpler.

-- Kaustuv