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

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

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.

/Andreas


On Mar 25, 2011, at 15.17 h, Joel Reymont wrote:

> It appears that I spoke to early as I'm still having trouble with  
> the implementation of my concept.
>
> What is it?
>
> I'm working with ZeroMQ and Thrift. The latter generates messages  
> using OCaml classes.
>
> I have request and reply messages in my system and replies are  
> created (dispatched) based on their request pair.
>
> A server should not have to know what messages it's dealing with.
>
> I would like to wrap each message class in a variant, particularly  
> helpful since some message classes are unions in the original Thrift  
> DSL but the Thrift OCaml code generator implements them poorly.
>
> Is my intent clear in the code below and if so how do I make it work?
>
> 	Thanks, Joel
>
> --- error
>
> File "x.ml", line 56, characters 26-35:
> Error: Signature mismatch:
>       Modules do not match:
>         sig
>           type obj = MyRequest.obj
>           type variant = MyRequest.variant = A
>           val make : unit -> int
>           val convert : 'a -> variant
>           val print : 'a -> unit
>         end
>       is not included in
>         Request
>       Values do not match:
>         val make : unit -> int
>       is not included in
>         val make : unit -> obj
>
> --- 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 =
> struct
>  type obj = private int
>  type variant = A
>  let make () = 1
>  let convert o = A
>  let print o = ()
> end
>
> module MyReply = functor (Req: Request) ->
> struct
>  type obj = private int
>  type variant = B
>  let make () = 2
>  let convert o = B
>  let print o = ()
>  let dispatch _ = B
> end
>
> module MyServer = Server (MyRequest) (MyReply)
>
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> drivers
> ---------------------+------------ 
> +---------------------------------------
> http://wagerlabs.com | @wagerlabs | http://www.linkedin.com/in/joelreymont
> ---------------------+------------ 
> +---------------------------------------
>
>
>
>
>
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