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|
(* Typed names *)
module Msg : sig
type 'a tag
type result = Result : 'a tag * 'a -> result
val write : 'a tag -> 'a -> unit
val read : unit -> result
type 'a tag += Int : int tag
module type Desc = sig
type t
val label : string
val write : t -> string
val read : string -> t
end
module Define (D : Desc) : sig
type 'a tag += C : D.t tag
end
end = struct
type 'a tag = ..
type ktag = T : 'a tag -> ktag
type 'a kind =
{ tag : 'a tag;
label : string;
write : 'a -> string;
read : string -> 'a; }
type rkind = K : 'a kind -> rkind
type wkind = { f : 'a . 'a tag -> 'a kind }
let readTbl : (string, rkind) Hashtbl.t = Hashtbl.create 13
let writeTbl : (ktag, wkind) Hashtbl.t = Hashtbl.create 13
let read_raw () : string * string = raise (Failure "Not implemented")
type result = Result : 'a tag * 'a -> result
let read () =
let label, content = read_raw () in
let K k = Hashtbl.find readTbl label in
let body = k.read content in
Result(k.tag, body)
let write_raw (label : string) (content : string) =
raise (Failure "Not implemented")
let write (tag : 'a tag) (body : 'a) =
let {f} = Hashtbl.find writeTbl (T tag) in
let k = f tag in
let content = k.write body in
write_raw k.label content
(* Add int kind *)
type 'a tag += Int : int tag
let ik =
{ tag = Int;
label = "int";
write = string_of_int;
read = int_of_string }
let () = Hashtbl.add readTbl "int" (K ik)
let () =
let f (type t) (i : t tag) : t kind =
match i with
Int -> ik
| _ -> assert false
in
Hashtbl.add writeTbl (T Int) {f}
(* Support user defined kinds *)
module type Desc = sig
type t
val label : string
val write : t -> string
val read : string -> t
end
module Define (D : Desc) = struct
type 'a tag += C : D.t tag
let k =
{ tag = C;
label = D.label;
write = D.write;
read = D.read }
let () = Hashtbl.add readTbl D.label (K k)
let () =
let f (type t) (c : t tag) : t kind =
match c with
C -> k
| _ -> assert false
in
Hashtbl.add writeTbl (T C) {f}
end
end;;
let write_int i = Msg.write Msg.Int i;;
module StrM = Msg.Define(struct
type t = string
let label = "string"
let read s = s
let write s = s
end);;
type 'a Msg.tag += String = StrM.C;;
let write_string s = Msg.write String s;;
let read_one () =
let Msg.Result(tag, body) = Msg.read () in
match tag with
Msg.Int -> print_int body
| String -> print_string body
| _ -> print_string "Unknown";;
|
