[Caml-list] Re: fighting the type system

[Joel Reymont <joelr1@gmail.com>]

A much reduced version. Help!

--- Util.ml

open ZMQ
open ZMQ.Socket
open Thrift

let make_proto = 
  let inbuf = Buffer.create 0
  and outbuf = Buffer.create 0 in
  let tx = new TBufferTransport.t inbuf outbuf in
  new TBinaryProtocol.t tx

type 'a request = < write : Protocol.t -> unit; .. > as 'a

module type Endpoint = 
sig 
  val request : unit -> 'a request
  val read_request : Protocol.t -> 'a request
end

module SimpleService (E: Endpoint) = 
struct 
  let server endpoint =  
    let proto = make_proto in
    E.read_request proto
end

--- A.ml

module U = Util
module T = AdCampaign_types

module Ads = 
struct
  let read_request = T.read_request
  let request () = new T.request
end

module M = U.SimpleService(Ads)

--- Error

File "src/ads.ml", line 10, characters 27-30:
Error: Signature mismatch:
       Modules do not match:
         sig
           val read_request : Thrift.Protocol.t -> T.request
           val request : unit -> T.request
         end
       is not included in
         U.Endpoint
       Values do not match:
         val request : unit -> T.request
       is not included in
         val request :
           unit -> < write : Thrift.Protocol.t -> unit; .. > U.request