Why are 3rd party libraries not found on the OCaml search path?

Question

My configuration is as follows:

OCaml is installed by Homebrew, according to its default recipe. It lives in /usr/local/Cellar/objective-caml/3.12.0/[bin,lib,share], the contents of which are symlinked out to /usr/local/[bin,lib,share].

A 3rd party library (LLVM) installed symlinks into /usr/local/lib/ocaml/*. Critically, /usr/local/lib/ocaml is itself not a symlink to the Homebrew Cellar, but a folder containing links to the individual files under the OCaml Cellar path, so these 3rd party library files are in the /usr/local/lib/ocaml/ path but not the original path of

The standard OCaml compilers/interpreter/build tools consistently fail to find these 3rd party libraries unless they are explicitly pointed there (e.g. with ocamlbuild -cflags -I,/usr/local/lib/ocaml).

ld.conf lists:

/usr/local/lib/ocaml/stublibs
/usr/local/lib/ocaml
/usr/local/lib/ocaml/site-lib/pcre

which would seem to suggest that the compiler search path be set correctly, but I am not familiar with the inner workings of the toolchain.

• Is this a known problem?
• Is there a way to print the OCaml search paths actually used by the standard tools?
• Assuming this is a consequence of the Homebrew configure and installation process (i.e. assuming that the problem is OCaml, as configured, assuming its actual lib path is /usr/local/Cellar/objective-caml/3.12.0/lib/ocaml rather than /usr/local/lib/ocaml), is it possible to force explicitly add additional search paths outside the --prefix during configuration?
• Is it possible to extend the search paths for the entire environment after installation (by editing config files, rather than having to resort to potential reinstallation)?

Answer 1

Indeed as ygrek pointed out, the answer is ocamlfind. OCamlfind maintains a list of findlib-enabled¹ OCaml packages installed on your system, and it's easy to link them. Use

ocamlfind list

To get the list of packages, which can be piped to grep etc.

ocamlfind query mypackage

To get the installation path for the package (for more see ocamlfind query --help)

ocamlfind ocamlc -package mypackage .....

To compile something using the package as a dependency (-linkpkg is used in the final linking step to build the executable, you don't need it with -c -o foo.cmo for example).

ocamlfind can also be used through ocamlbuild. Prior to ocaml 3.12 you add to hack a bit the myocamlbuild.ml file (link), but since 3.12 it's dead easy: use package(foo) in the ocamlbuild tags if you want to use ocamlfind's package foo, and add option -use-ocamlfind to ocamlbuild's invocation.

¹: ocamlfind is the lingua franca of OCaml packages. If some of your third libraries don't register themselves through ocamlfind, you should hunt them, write a META file (it's easy), and send it to the library maintainer.