Actually works now?

jslib/dune

@@ -1,3 +1,5 @@
 (melange.emit
  (target main)
+ (preprocess
+  (pps melange.ppx))
  (libraries hcfg))

jslib/main.ml

@@ -1,10 +1,46 @@
+type bytearray
+external create_bytearray: Bytes.t -> bytearray = "Uint8Array" [@@mel.new]
+
+module JsValue = struct 
+  type jsvalue =
+    | NUMBER of Js.Float.t
+    | STRING of Js.String.t
+    | BINARY of bytearray
+    | NULL of unit Js.Nullable.t
+    | ARRAY of jsvalue Js.Array.t
+    | OBJECT of jsvalue Js.Dict.t
+end
+
 let parse str = 
-  let rec hvalue_to_js x = match x with
-      | Hcfg.Parser.STRING s -> Js.Json.string s
-      | Hcfg.Parser.INTEGER i -> Js.Json.number (float_of_int i)
-      | Hcfg.Parser.FLOAT f -> Js.Json.number f
-      | Hcfg.Parser.BINARY _ -> failwith "Binary not supported"
-      | Hcfg.Parser.NULL -> Js.Json.null
-      | Hcfg.Parser.ARRAY a -> Js.Json.array (Array.of_list (List.map hvalue_to_js a))
-      | Hcfg.Parser.OBJECT o -> Js.Json.object_ (Js.Dict.fromList (List.map (fun (k, v) -> (k, hvalue_to_js v)) (Hcfg.Parser.Obj.to_list o))) in
-  Hcfg.Lexer.generate_tokens str |> Hcfg.Parser.parse |> hvalue_to_js
+  let _hvalue_to_js = [%mel.raw {|
+    function _hvalue_to_js(hvalue) {
+      switch (hvalue.TAG) {
+          case 0:
+              // Number
+          case 1:
+              // String
+          case 2:
+              // Binary
+          case 3:
+              // Null
+              return hvalue._0
+          case 4:
+              return hvalue._0.map(_hvalue_to_js)
+              // Array
+          case 5:
+              // Obj
+              return Object.fromEntries(
+                  Object.entries(hvalue._0).map(([k, v]) => [k, _hvalue_to_js(v)])
+              )
+      }
+  }
+  |}] in
+  let rec hvalue_to_js = function
+      | Hcfg.Parser.STRING s -> JsValue.STRING s
+      | Hcfg.Parser.INTEGER i -> JsValue.NUMBER (float_of_int i)
+      | Hcfg.Parser.FLOAT f -> JsValue.NUMBER f
+      | Hcfg.Parser.BINARY b -> JsValue.BINARY (create_bytearray b)
+      | Hcfg.Parser.NULL -> JsValue.NULL (Js.Nullable.null)
+      | Hcfg.Parser.ARRAY a -> JsValue.ARRAY (Array.of_list (List.map hvalue_to_js a))
+      | Hcfg.Parser.OBJECT o -> JsValue.OBJECT (Js.Dict.fromList (List.map (fun (k, v) -> (k, hvalue_to_js v)) (Hcfg.Parser.Obj.to_list o))) in
+  Hcfg.Lexer.generate_tokens str |> Hcfg.Parser.parse |> hvalue_to_js |> _hvalue_to_js

lib/parser.ml

@@ -68,6 +68,7 @@ module Parser = struct
       | (OBJECT a, OBJECT b) -> Obj.equal equal a b
       | _ -> false 
 
+  let stringify_bytes b = Bytes.fold_left (fun acc b -> acc ^ Printf.sprintf "\\x%2x" (Char.code b)) "" b
 
   let rec hvalue_to_string = function
     | INTEGER a -> "INTEGER: " ^ Int.to_string a

test/test.hcfg

@@ -3,6 +3,7 @@
     key: "value",
     /* this is a comment */
     other_key: 100,
+    nulled: null,
     floating: 123f,
     other_float: 123.3,
     bin: b"test",