simplify errors and exns

examples/decode.ml

@@ -28,5 +28,5 @@ let _ =
   let json = {|{ "y": 42 } |} |> Json.parseOrRaise in
   match Json.Decode.(field "x" int json) with
   | x -> Js.log x
-  | exception Json.Decode.DecodeError err ->
-      Js.log ("Error:" ^ Json.Decode.error_to_string err)
+  | exception Json.Of_json_error err ->
+      Js.log ("Error:" ^ Json.of_json_error_to_string err)

ppx/browser/ppx_deriving_json_runtime.ml

@@ -6,8 +6,6 @@ let to_json t = t
 let of_json t = t
 let to_string t = Js.Json.stringify t
 
-exception Of_string_error of string
-
 let of_string s =
   try Js.Json.parseExn s
   with exn ->
@@ -20,13 +18,13 @@ let of_string s =
       (* msg really cannot be None in browser or any sane JS runtime *)
       Option.value msg ~default:"JSON error"
     in
-    raise (Of_string_error msg)
+    raise (Json.Of_string_error msg)
 
-type error = Json.Decode.error =
+type error = Json.of_json_error =
   | Json_error of string
   | Unexpected_variant of string
 
-exception Of_json_error = Json.Decode.DecodeError
+exception Of_json_error = Json.Of_json_error
 
 let of_json_error msg = raise (Of_json_error (Json_error msg))
 

src/Json.ml

@@ -374,13 +374,6 @@ end
 
 module Decode = struct
   type 'a decoder = 'a of_json
-  type error = Json_error of string | Unexpected_variant of string
-
-  let error_to_string = function
-    | Json_error msg -> msg
-    | Unexpected_variant tag -> "unexpected variant: " ^ tag
-
-  exception DecodeError of error
 
   let id json = json
   let bool = Of_json.bool

src/Json.mli

@@ -126,6 +126,8 @@ val to_json : json to_json
 (** The type of a error which occurs during decoding JSON values. *)
 type of_json_error = Json_error of string | Unexpected_variant of string
 
+val of_json_error_to_string : of_json_error -> string
+
 type exn +=
   | Of_json_error of of_json_error
         (** The exception raised when a decoding error occurs *)
@@ -263,12 +265,6 @@ module Decode : sig
   type 'a decoder = 'a of_json [@@deprecated "Use `of_json` instead"]
   (** The type of a decoder combinator *)
 
-  type error = Json_error of string | Unexpected_variant of string
-
-  val error_to_string : error -> string
-
-  exception DecodeError of error
-
   val id : t of_json [@@deprecated "Use `of_json` instead"]
   val bool : bool of_json [@@deprecated "Use `Of_json.bool` instead"]
   val float : float of_json [@@deprecated "Use `Of_json.float` instead"]