我该如何将Eliom客户端的user_type传递给服务器？

Question

http://ocsigen.org/eliom/manual/server-params#h5o-3显示了一个接受用户定义类型的GET服务的示例。我想从客户端调用带有user_type的coservice，在客户端使用相同的类型。现在看来似乎应该是可能的，但我得到

ocsigenserver: main: Exn during page generation: Failure("User service parameters 'foo' type not supported client side.") (sending 500) 

当我尝试

{shared{ 
    open Eliom_lib 
    open Eliom_content 
    open Html5.D 

    type foo = A | B 
    let foo_of_string = function "a" -> A | "b" -> B | _ -> raise (Failure "foo_of_string: unsupported foo") 
    let string_of_foo = function A -> "a" | B -> "b" 
}} 

let foo_to_div foo : Html5_types.div Html5.elt Lwt.t = match foo with A -> Lwt.return (div [pcdata "aye"]) | B -> Lwt.return (div [pcdata "bee"]) 
let foo_service = 
    Eliom_registration.Ocaml.register_post_coservice' 
    ~post_params:Eliom_parameter.(user_type foo_of_string string_of_foo "foo") 
    (fun() foo -> foo_to_div foo) 

{client{ 
    let test() = 
    Eliom_client.call_ocaml_service ~service:%foo_service() A 
}} 


(* Boilerplate from eliom-distillery: *) 
module Testing_app = Eliom_registration.App 
    (struct let application_name = "testing" end) 
let main_service = 
    Eliom_service.App.service ~path:[] ~get_params:Eliom_parameter.unit() 
let() = 
    Testing_app.register ~service:main_service 
    (fun()() -> Lwt.return (Eliom_tools.F.html ~title:"foo" 
           Html5.F.(body [ pcdata "bar" ]))) 

---

我也尝试使用server_function，但后来我跑进如何获得的问题div作为json;做

type div_elt = Html5_types.div Eliom_content.Html5.elt 
let div_elt_json = Json.t<div_elt> 

给我Error: Unbound module Html5_types.Json_div

Answer 1

一次偶然的机会我向下滚动了一下阅读服务器功能后，发现http://ocsigen.org/eliom/4.1/manual/clientserver-communication#h5o-5它说，而不是做

{shared{ 
    type foo = A | B deriving (Json) 
    type foo_json = Json.t<foo> 
}} 
let foo_service = 
    Eliom_registration.Ocaml.register_post_coservice' 
    ~post_params:Eliom_parameter.(ocaml "param" foo_json) 
    (fun() foo -> foo_to_div foo) 

这一点也适用= d

（虽然我仍然会倾向于使用server_function，这看起来更简洁一些。）