Re: [Caml-list] substituting recursive types inside a signature

[Ashish Agarwal <agarwal1975@gmail.com>]

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I pasted the wrong code. Slightly less typing is possible by doing "include
M" in N's implementation.

On Wed, Nov 4, 2015 at 10:22 PM, Ashish Agarwal <agarwal1975@gmail.com>
wrote:

> On Wed, Nov 4, 2015 at 9:10 PM, Jacques Garrigue <
> garrigue@math.nagoya-u.ac.jp> wrote:
>
> the code you wrote is exactly equivalent to:
>>
>>    include (((module type of M) with type t = M.t) with type u = M.u)
>>
>
> And the parentheses here don't matter right, so this is the same as:
>
> include module type of M
>     with type t = M.t
>     with type u = M.u
>
> So then why do we have the "and" syntax at all?
>
> Well, I can use manifest types to work around this, at the expense of some
> manual typing. Here's what works:
>
> $ cat foo.ml
> module M = struct
>   type t = A | B of u
>   and u = C of t
> end
>
> module N : sig
>   type t = M.t = A | B of u
>   and u = M.u = C of t
>   val f : t -> t
> end = struct
>   type t = M.t = A | B of u
>   and u = M.u = C of t
>   let f x = x
> end
>
> let x : M.t = M.A
> let _ = N.f x
>
>

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