title: OCaml and Opam: unbound module Core
body: <p>I'm trying to get an OCaml environment set up, and I've followed the instructions from appendix A of the Real World OCaml beta. I set up opam, and installed a version of OCaml with the command</p>
  <pre><code>$ opam switch 4.01.0dev+trunk
  </code></pre>
  <p>which passed fine. I then did an</p>
  <pre><code>$ eval `opam config env`
  </code></pre>
  <p>to pull in the changes. I'm running the correct top level, as</p>
  <pre><code>$ which ocaml
  </code></pre>
  <p>outputs</p>
  <pre><code>/home/bryan/.opam/4.01.0dev+trunk/bin/ocaml
  </code></pre>
  <p>I installed the Core package from Jane street, with the command</p>
  <pre><code>$ opam install core
  </code></pre>
  <p>Both ocamlfind and opam search show that the package was installed correctly. However when I try to open it either from the repl or in a file, I get the error 'unbound module Core'. e.g.</p>
  <pre><code>$ ocaml
  # open Core;;
  Error: Unbound module Core
  </code></pre>
  <p>Is there something I'm missing here? Why can't OCaml find my installed module?</p>