I’m working on a project in OCaml using Dune, and I’m encountering an “Unbound value” error for a function defined in a custom module. I’ve ensured that the module is correctly defined and imported, but the error persists.

Relevant files:

lib/markdown.ml

module Markdown = struct
  open Omd

  let convert_markdown_to_html content =
    content |> Omd.of_string |> Omd.to_html
end

lib/lib.ml

module Markdown = Markdown
module Template = Template
module SiteConfig = SiteConfig
module Generator = Generator

lib/generator.ml

open Core
open Core_unix

module Generator = struct
  let generate_site config =
    let dh = Core_unix.opendir "content/" in
    let rec read_all dh acc =
      match Core_unix.readdir_opt dh with
      | None -> List.rev acc
      | Some entry -> read_all dh (entry :: acc)
    in
    let markdown_files = read_all dh [] in
    Core_unix.closedir dh;
    List.iter markdown_files ~f:(fun file ->
      let input_path = "content/" ^ file in
      let output_path = "output/" ^ (Filename.chop_suffix file ".md") ^ ".html" in
      let content = In_channel.read_all input_path in
      let html_content = Markdown.convert_markdown_to_html content in
      let template = In_channel.read_all "templates/default.html" in
      let full_content = Template.render_template template html_content in
      Out_channel.write_all output_path ~data:full_content
    )
end

lib/dune

(library
 (name ocamlpress)
 (public_name ocamlpress)
 (libraries str yojson omd core core_unix))

bin/dune

(executable
 (public_name ocamlpress)
 (name main)
 (libraries ocamlpress omd cohttp lwt cmdliner))

Error Message:

When I run dune build, I get the following error:

File "lib/generator.ml", line 28, characters 25-58:
28 |       let html_content = Markdown.convert_markdown_to_html content in
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: Unbound value Markdown.convert_markdown_to_html

I’ve tried cleaning and rebuilding the project using dune clean and dune build, but the error persists.
The dune and dune-project files are correctly set up according to Dune documentation.
I’m using OCaml version 4.12.0 and Dune version 2.9.1.

Why am I getting the “Unbound value” error for Markdown.convert_markdown_to_html, and how can I resolve this issue?