Here's an attempt to clarify the question:

I have a functor F and a functor G. I apply F to module M outside of G to
create F', and within G I also apply F to M to create F''. Additionally, G
is applied to M to create G'. How do I make the compiler understand that F'
outside G' is the same as F'' inside G'?

Yotam


On Wed, Sep 3, 2014 at 1:20 PM, Yotam Barnoy <yotambarnoy@gmail.com> wrote:

> Working with ocaml's functional data structures has quickly become a job
> of connecting different functors together, and I'd appreciate some help.
>
> I have the following layout:
>
> module rec OrderedKey : OrderedKeyType = struct
>     type t = Value.value_t
>     let compare = compare
>     let filter_idxs idxs = function
>       | Value.VTuple l -> Value.VTuple(list_filter_idxs idxs l)
>       | _ -> invalid_arg "not a vtuple"
>     end
>
> and ValueBag : IBag.S with type elt = Value.value_t =
>   IBag.Make(OrderedKey)
>
> and ValueMMap : IMultimap.S with type elt = Value.value_t and type bag =
> ValueBag.t =
>   IMultimap.Make(OrderedKey)
>
> and Value : sig ... type value_t = ... end = Value
>
> The situation is as such: my multimap (IMultimap) contains an internal
> specialization of the IBag functor called an InnerBag. It attempts to
> return said bag, which is equivalent to the external ValueBag in structure.
> However, I don't know how to tell ocaml that the type 'bag' which is
> abstract in IMultimap is exactly the same as the external ValueBag. I tried
> to do that above, but what I get is a mismatch between IMultimap's internal
> InnerBag.t and the external ValueBag.t.
>
> Any help would be appreciated.
>
> Yotam
>
>