Re: [Caml-list] Re: module typing issue

[Andreas Rossberg <rossberg@mpi-sws.org>]

Well, you have to make it transparent in the Request signature then.  
Then you should be able to say Req.A -> 1.

/Andreas


On Mar 25, 2011, at 16.57 h, Joel Reymont wrote:

>
> On Mar 25, 2011, at 3:46 PM, Andreas Rossberg wrote:
>
>> I don't think it ever makes sense to define private type  
>> abbreviations in a structure - they are intended for use in  
>> signatures. Just drop the private from your example.
>
> This compiles but fails as soon as I try to replace dispatch in  
> MyReply (bottom) with
>
>  let dispatch = function | A -> 1
>
> This is obvious conceptually as MyReply doesn't know about the  
> variant type defined in MyRequest.
>
> How do I make let MyReply know about it?
>
> 	Thanks, Joel
>
> --- x.ml
>
> module type Message =
> sig
> type obj
> type variant
> val make : unit -> obj
> (* encapsulate object in a variant type *)
> val convert : obj -> variant
> val print : obj -> unit
> end
>
> module type Request =
> sig
> include Message
> end
>
> (* dispatches based on a request *)
>
> module type Reply = functor (Req : Request) ->
> sig
> include Message
> val dispatch : Req.variant -> obj
> end
>
> module Server (Req : Request) (REP : Reply) =
> struct
> module Rep = REP(Req)
> let server =
>   while true do
>     let req = Req.make () in
>     let var = Req.convert req in
>     let rep = Rep.dispatch var in
>     Req.print req;
>     Rep.print rep
>   done
> end
>
> module MyRequest : Request =
> struct
> type obj = int
> type variant = A
> let make () = 1
> let convert o = A
> let print o = ()
> end
>
> module MyReply : Reply = functor (Req: Request) ->
> struct
> type obj = int
> type variant = B
> let make () = 2
> let convert o = B
> let print o = ()
> let dispatch _ = 2
> end
>
> module MyServer = Server (MyRequest) (MyReply)
>
>
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