Error: Unbound module ... in Ocaml

I have just installed a library called Apron, the installation seems to be done:

@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

And I tried a first example:

(* 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.Abstr开发者_开发知识库act1.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;;
...

However ocaml -c file.ml gives me Error: Unbound module Apron which happens on open Apron;;

Does anyone know why I could not load the Apron module? Thank you very much!

---

I should indicate the path of the Apron library with '-I' options. As it is installed in the standard library of OCaml, you only need to compile with:

ocamlc -I +apron -c file.ml