How to export a value?

[francoisthire]

I am writing a VScode extension using the Brr library.

I don't have a minimal reproducible example but here is my snippet:

 let activate =
    Jv.callback ~arity:1 (fun context ->
        Console.log "Congratulations, your extension for kalkulu is now active!";
        let callback () = Vscode.Window.show "Hello world!" in
        let disposable =
          Vscode.Command.register ~command:"extension.helloWorld" ~callback
        in
        Vscode.Extension_context.subscribe context disposable)
  in
  (* Js.export "activate" @@ activate *)
  Jv.set Jv.global "activate" activate

If I uncomment the Js.export line, it works, but the Jv.set does not.

I am not sure to understand what is going on. I observe the compiled JS is a little bit different. In particular Js.export uses "jsoo_exports` value.

I have tried to read the FFI cookbook, but I did not find an explanation. Is this expected? Why?

[dbuenzli]

It's not clear what "works" mean. I guess it depends a bit when activate needs to be available. Perhaps the extension needs to have it before the OCaml module initialisation code is executed ?

[francoisthire]

What VScode prompts when I use the Jv.set approach is similar to a not found error. Somehow it does not find the activate function.

I am not sure how I can debug that, the generated code is complex. What changes seems to be the following lines:

With Js.export:

 activate =
    (* ... *)
   caml_call1(caml_call1(Js_of_ocaml_Js[50], "activate"), activate);
   var Dune_exe_Main = [0];
   runtime.caml_register_global(16, Dune_exe_Main, "Dune__exe__Main");
   return;
  }
  (globalThis));

While with the Jv.set approach:

  activate =
     (* ... *)
   Jv[12]["activate"] = activate;
   var Dune_exe_Main = [0];
   runtime.caml_register_global(15, Dune_exe_Main, "Dune__exe__Main");
   return;
  }
  (globalThis));

[dbuenzli]

Perhaps @hhugo can shed a light ?

[dbuenzli]

For reference this is how Jv.global is defined

[dbuenzli]

Could you perhaps try to rename the activate OCaml value to something else.

[francoisthire]

I have tried to rename the OCaml value but I get the same error.

[dbuenzli]

In eeeff51 I tried to export a function as mentioned in the cookbook and it works in FF, Safari and Chrome. So I'm not sure exactly why the Js.export is needed.

I tentatively try to ping @hhugo again if he can maybe shed some light.