I want to have an OCaml toplevel in a browser having ppx_deriving.show
support.  I tried to include "ppx_deriving.show" as in the attached
dune file, but the resulting toplevel does not appear to understand
[@@deriving show] directive.

With the attached files, I can at least print a message in a browser:

- create a directory
- save the attached four files
- dune build
- open index.html

In index.html, I run the toplevel with

print_endline "hello";;

and 

type test_t = {x:int}[@@deriving show];;
print_endline (show_test_t {x=1});;

The former succeeds, but the latter produces:

Error: Unbound value show_test_t

How can I create an OCaml toplevel that produces

{ x = 1 }
- : unit = ()

for the latter?  Thank you in advance!

Sincerely,

-- 
Kenichi Asai