Two remarks:

1. You should use "ocamlfind" to provide you with machine-portable path
information on OCaml libraries (this only works with libraries that have
ocamlfind support, but that's essentially all libraries worth using, and
otherwise it's a packaging bug that you should report to the library author
or distributor). So instead of the machine-dependent LIB variable, you
could just set:
  LIB=-I,$(shell ocamlfind query lacaml)

2. You don't actually need this include-handling logic as ocamlfind can
deal with that for you. To use it from ocamlbuild, the magic option is
"-use-ocamlfind", and then using "-pkg(s)" instead of "-lib(s)" option. I
was able to reproduce your problem on a test file, and fixed it with the
following Makefile:

all:
    ocamlbuild -use-ocamlfind -pkgs bigarray,lacaml,str,unix -verbose 2
molexc.native

clean:
    ocamlbuild -clean

doc:
    ocamlbuild -use-ocamlfind -pkgs bigarray,lacaml,str,unix
molexc.docdir/index.html

(To see a list of available ocamlfind package, use "ocamlfind list"; see
_build/_log for the actual compilation lines that ocamlbuild uses, if you
want to reproduce them by hand.)

On Thu, Feb 21, 2013 at 2:25 PM, Elisa Rebolini <erebolini@gmail.com> wrote:

> I've installed lacaml 7.0.3 by following the installation procedure
>         'ocaml setup.ml -configure'
>         'ocaml setup.ml -build'
>         'ocaml setup.ml -install'
> The path to the lacaml package is /usr/local/lib/ocaml/site-lib/lacaml
> and my Makefile is
>
> hostname := $(shell uname -n)
>
> # Default
> LIB=-I,+site-lib/lacaml
>
> ifeq ($(hostname),clastos)
> LIB=-I,+site-lib/lacaml
> endif
>
> ifeq ($(hostname),bulle)
> LIB=-I,/usr/local/lib/ocaml/3.12.1/lacaml
> endif
>
> all:
>         ocamlbuild -libs bigarray,lacaml,str,unix -verbose 2 -cflags $(LIB)
> -lflags $(LIB) molexc.native
>
> clean:
>         ocamlbuild -clean
>
> doc:
>         ocamlbuild -libs bigarray,lacaml,str,unix -verbose 2 -cflags $(LIB)
> -lflags $(LIB) molexc.docdir/index.html
>
> thanks
> --
> Elisa
>
> Le 21/02/2013 14:11, Gabriel Scherer a écrit :
> > It would help to have more precise information about your setup. Could
> you
> > detail how you installed lacaml on your system, and provide a directory
> > tarball for a simple project allowing to reproduce your problem (with the
> > _tags file etc.)?
> >
> > On Thu, Feb 21, 2013 at 2:07 PM, Elisa Rebolini <erebolini@gmail.com>
> wrote:
> >
> > Hello list,
> > I'm developping a quantum chemistry software with ocaml and use lacaml
> > as a binding to the LAPACK and BLAS libraries.
> > I have a warning at the compilation with ocamlbuild
> >         Warning: Failed to build the module Lacaml requested by ocamldep
> >         mid rule ocaml: ml -> cmo & cmi (%=parser_epsilon ): cache hit
> > but the compilation is still successful and the program works as
> > expected but when I try to compile the documentation I have an error
> >         Error: Unbound module Lacaml
> > I'm not very skilled (yet?) with caml so any help would be very much
> > appreciated.
> > Thanks a lot
> >>
> >> --
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> >>
> >
>