Hi Shayne,

You can add a constrain to your functor arguments :

module type MUL = functor (E : EQ) (N : NUM with type t = E.t) ->
    MUL_S with module N := N and module E := E

Cheers,
Nicolas

On Fri, Oct 28, 2016 at 3:14 PM, Shayne Fletcher <
shayne.fletcher.50@gmail.com> wrote:

>
> On Fri, Oct 28, 2016 at 9:01 AM, Nicolas Ojeda Bar <
> nicolas.ojeda.bar@lexifi.com> wrote:
>
>>
>> One approach is to name the *output* signature of the functors:
>>
>> module type EQ_PROD_S = sig
>>     module X : EQ
>>     module Y : EQ
>>     type t = X.t * Y.t
>>     val eq: t * t -> bool
>> end
>>
>
> ​Sorry to be a bother. Got another one for you Nicolas​!
>
> How do I achieve the intent of this:
>
> module type EQ = sig
>   type t
>   val eq : t * t -> bool
> end
>
> module type NUM = sig
>   type t
>   val from_int : int -> t
>   val ( + ) : t -> t -> t
> end
>
> module type MUL_S = sig
>   module N : NUM
>   module E : EQ  with type t := N.t
>
>   type t = N.t
>   val mul : t -> t -> t
> end
>
> module type MUL = functor (E : EQ) (N : NUM) -> MUL_S with module N := N
> and module E := E
>
> The idea is that the modules satisfying EQ and NUM must agree in their
> type t and MUL brings them together and adds a 'mul' function.
>
> --
> Shayne Fletcher
>