title: Error: Unbound module ... in Ocaml
body: <p>I have just installed a library called <code>Apron</code>, the installation seems to be done:</p>
  
  <pre><code>@ubuntu$ find -name "*apron*"
  ./lib/libapron_debug.so
  ./lib/libapron.a
  ./lib/libapron.so
  ./lib/libapron_debug.a
  ./local/lib/ocaml/3.11.2/stublibs/dllapron_caml.so.owner
  ./local/lib/ocaml/3.11.2/stublibs/dllapron_caml.so
  ./local/lib/ocaml/3.11.2/apron
  ./local/lib/ocaml/3.11.2/apron/libapron_caml_debug.a
  ./local/lib/ocaml/3.11.2/apron/apron.cmxa
  ./local/lib/ocaml/3.11.2/apron/libapron_caml.a
  ./local/lib/ocaml/3.11.2/apron/apron.cmi
  ./local/lib/ocaml/3.11.2/apron/apron.cmx
  ./local/lib/ocaml/3.11.2/apron/apron.a
  ./local/lib/ocaml/3.11.2/apron/apron.cma
  </code></pre>
  
  <p>And I tried a first example:</p>
  
  <pre><code>(* with default setting:
  
  apronppltop -I $MLGMPIDL_INSTALL/lib -I $APRON_INSTALL/lib
  
  #load "gmp.cma";;
  #load "apron.cma";;
  #load "box.cma";;
  #load "oct.cma";;
  #load "polka.cma";;
  #load "ppl.cma";;
  #load "polkaGrid.cma";;
  
  #install_printer Apron.Linexpr1.print;;
  #install_printer Apron.Texpr1.print;;
  #install_printer Apron.Lincons1.print;;
  #install_printer Apron.Generator1.print;;
  #install_printer Apron.Abstract1.print;;
  
  let environment_print fmt x = Apron.Environment.print fmt x;;
  let lincons1_array_print fmt x = Apron.Lincons1.array_print fmt x;;
  let generator1_array_print fmt x = Apron.Generator1.array_print fmt x;;
  
  #install_printer Apron.Var.print;;
  #install_printer environment_print;;
  #install_printer lincons1_array_print;;
  #install_printer generator1_array_print;; *)
  open Apron;;
  ...
  </code></pre>
  
  <p>However <code>ocaml -c file.ml</code> gives me <code>Error: Unbound module Apron</code> which happens on <code>open Apron;;</code></p>
  
  <p>Does anyone know why I could not load the Apron module? Thank you very much!</p>