Unbound Module when using Dream eml pre-processor

Question

I'm trying to learn OCaml by way of building a website with this lovely library I found called Dream (https://aantron.github.io/dream/), but I've run into an issue when trying to work with the template preprocessor! My code is copied straight from the 7-template example from the library's github page, and everything seems to work, up until the point I run dune build. The preprocessor, dream_eml, converts my templated code with jsx style html markup to less pretty, but more compilable, OCaml code, but when it does, it inserts a reference to the module Dream_pure, and my compiler is saying that Dream_pure is an unbound module! Below you can find the preprocessed code as well as my dune file!

dune file:

(executable
 (name jenr_dev_server)
 (libraries base core dream)
 (preprocess (pps lwt_ppx)))

(rule
 (targets jenr_dev_server.ml)
 (deps jenr_dev_server.eml.ml)
 (action (run dream_eml %{workspace_root}/src/server/%{deps})))

expanded code:

#1 "./src/server/jenr_dev_server.eml.ml"
let render param =
let ___eml_buffer = Buffer.create 4096 in
(Buffer.add_string ___eml_buffer "<html>\n<body>\n  <h1>The URL parameter was ");
(Printf.bprintf ___eml_buffer "%s" (Dream_pure.Formats.html_escape (
#4 "./src/server/jenr_dev_server.eml.ml"
                                  param 
)));
(Buffer.add_string ___eml_buffer "!</h1>\n</body>\n</html>\n\n");
(Buffer.contents ___eml_buffer)
#8 "./src/server/jenr_dev_server.eml.ml"
let () =
  Dream.run
  @@ Dream.logger
  @@ Dream.router [

    Dream.get "/:word"
      (fun request ->
        Dream.param request "word"
        |> render
        |> Dream.html);

  ]

the error message

File "../../src/server/jenr_dev_server.eml.ml", line 4, characters 36-66:
Error: Unbound module Dream_pure

I tried reinstalling the library on my opam switch with opam install dream as well as reconfiguring the dune file to match the example from the library's repository

What does your `dune_project` file look like? – glennsl Jul 23 '23 at 20:33 — glennsl, Jul 23 '23 at 20:33

score 0 · Answer 1 · answered Jul 24 '23 at 08:22

I suspect that you've disabled implicit_transitive_deps in your dune_project file. As the documentation states:

Then all dependencies directly used by a library or an executable must be added in the libraries field.

Which means you'll have to add dream-pure to libraries in your dune file.

It seems it could also be fixed in dream by adding re_export to dream-pure in its libraries stanza.

Unbound Module when using Dream eml pre-processor

1 Answers1