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From: Thomas Braibant <thomas.braibant@gmail.com>
Date: Tue, 13 Jan 2015 18:09:54 +0100
Message-ID: <CAHR=Vkx1Lb43qh5QtcnKM2tw=64m6NuU8xsd0CoFR5P7tP2X8g@mail.gmail.com>
To: OCaML Mailing List <caml-list@inria.fr>
Content-Type: text/plain; charset=UTF-8
Subject: [Caml-list] Quizz

Hi list,

Here is a quizz that can easily be solved using OCaml (version
4.02.1), but it would be less fun than trying to infer which functions
are accepted.

```
module type S = sig val test : 'a list end

type t = (module S)

let a (x : t) =
  let module M = (val x) in
  List.length M.test

let b (module M : S) =
  List.length M.test

let c ((module M) : t) =
  List.length M.test

let d (module M : t) =
  List.length M.test

let e (x : (module S)) =
  let module M = (val x) in
  List.length M.test

let f ((module M) : (module S)) =
  List.length M.test

let g : (module S) -> int = fun (module M) ->
  List.length M.test

let h ((module M) : (module sig val test : 'a list end)) =
  List.length M.test

```
(I am sure I have missed interesting variations, though.)

I have read through

http://caml.inria.fr/pub/docs/manual-ocaml/types.html,
http://caml.inria.fr/pub/docs/manual-ocaml/modtypes.html
http://caml.inria.fr/pub/docs/manual-ocaml/extn.html#sec230

but what I do not get is how to make a variation of `h` work. That is,
I would like to inline the module signature. Is that possible?

Best,
Thomas