I want to create a web page where I can execute an OCaml expression
that mentions a prebuilt user-defined library.  I find the following
example in the js_of_ocaml/toplevel repository:

https://github.com/ocsigen/js_of_ocaml/tree/master/toplevel/examples/eval

Can I extend this example so that the toplevel is compiled with a
user-defined library?  The attached program contains the following
where the first three files are copied from the example in the
js_of_ocaml/toplevel repository.

toplevel/ -- dune
          -- eval.ml
          -- index.html
          -- fac/ -- dune
                  -- fac.ml

I intend that fac.ml is compiled as a library and I want to use it in
the toplevel.  I added "fac" in the libraries stanza of the toplevel
dune file (as in the attached file):

(executables
  (names eval)
  (libraries
    fac
    js_of_ocaml-compiler
    js_of_ocaml-toplevel)
  (link_flags (:standard -linkall))
  (preprocess (pps js_of_ocaml-ppx)))

Naturally, fac.ml is compiled and I can use it in the eval.ml, but it
is not visible from the toplevel.  I included the following part in
the index.html (as in the attached file):

<script type="text/ocaml" stdout="script3" stderr="script3">
  Fac.go 3;;
</script>
<div id="script3"> </div>

but the output says:

File "/dev/fake_stdin", line 2, characters 6-12:
Error: Unbound module Fac

Thank you in advance.

--
Kenichi Asai