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module Ty = struct
type 'a witness = ..
exception Not_equal
type (_, _) eq = Eq : ('a, 'a) eq
module type Ty = sig
type t val witness : t witness
val eq: 'a witness -> ('a, t) eq
end
type 'a id = (module Ty with type t = 'a)
let new_id (type a) () =
let module Ty = struct
type t = a
type 'a witness += Ty : t witness
let witness = Ty
let eq (type b) : b witness -> (b, t) eq =
function Ty -> Eq | _ -> raise Not_equal
end in
(module Ty : Ty with type t = a)
let eq : type a b. a id -> b id -> (a, b) eq =
fun (module TyA) (module TyB) -> TyB.eq TyA.witness
end
type descr = {
name: string ;
descr: string option ;
example: string option
}
type 'a t = {
id: 'a Ty.id;
destruct: string -> ('a, string) result ;
construct: 'a -> string ;
description: descr ;
}
let make ?example ?descr ~name ~destruct ~construct () =
let id = Ty.new_id () in
let example = match example with
| None -> None
| Some example -> Some (construct example) in
let description = { name ; descr; example } in
{ description ; id ; construct ; destruct }
let descr (ty: 'a t) = ty.description
let int ?descr ?example name =
let int_of_string s =
try Ok (int_of_string s)
with Failure _ ->
Error (Printf.sprintf "Cannot parse integer value: %S." s) in
make ?example ?descr ~name ~destruct:int_of_string ~construct:string_of_int ()
let float ?descr ?example name =
let float_of_string s = match float_of_string_opt s with
| Some f -> Ok f
| None -> Error (Printf.sprintf "Cannot parse float value: %S." s) in
make ?example ?descr ~name ~destruct:float_of_string ~construct:string_of_float ()
let int32 ?descr ?example name =
let int32_of_string s = match Int32.of_string_opt s with
| Some i -> Ok i
| None -> Error (Printf.sprintf "Cannot parse int32 value: %S." s) in
make ?example ?descr ~name ~destruct:int32_of_string ~construct:Int32.to_string ()
let int64 ?descr ?example name =
let int64_of_string s = match Int64.of_string_opt s with
| Some i -> Ok i
| None -> Error (Printf.sprintf "Cannot parse int64 value: %S." s) in
make ?descr ?example ~name ~destruct:int64_of_string ~construct:Int64.to_string ()
let string ?descr ?example name =
make ?descr ?example ~name ~destruct:Result.ok ~construct:(fun s -> s) ()