title: How to include a local library to an executable with dune ocaml
body: <p>I have a project structured like this :</p>
  <pre><code>root/
  |—— dune-project
  |—— lib/
  |  |—— dune
  |  |—— Readertsp.ml
  |  |-- ...
  |
  |—— bin/
  |  |—— dune
  |  |—— bin.ml
  </code></pre>
  <p><code>bin.ml</code> :</p>
  <pre class="lang-ml prettyprint-override"><code>let city_config = &quot;ch130&quot; in
  let path = Readertsp.open_path city_config in ();;
  </code></pre>
  <p><code>dune</code>:</p>
  <pre><code>(executable
   (name MCTS_main)
   (libraries graphics mcts)
  )
  </code></pre>
  <p><code>Readertsp.ml</code> : <a href="https://pastebin.com/U0h69uRy" rel="nofollow noreferrer">https://pastebin.com/U0h69uRy</a></p>
  <p><code>dune</code> :</p>
  <pre><code>(library
   (name mcts)
   (modules Readertsp)
   (libraries graphics))
  </code></pre>
  <p>When I try dune build, I get this error :</p>
  <pre class="lang-js prettyprint-override"><code>File &quot;tests/MCTS_main.ml&quot;, line 3, characters 0-19:
  3 | Readertsp.open_path city_config;;
      ^^^^^^^^^^^^^^^^^^^
  Error: Unbound module Readertsp
  </code></pre>
  <p>Do you know how to fix this ?</p>