Using an external library

Imagine you want to use lablgl and lablglut in your OCaml project. These libraries are not currently directly known by ocamlbuild so you have to declare them. To do so you have to write a plugin in a file myocamlbuild.ml at the root of your project:

open Ocamlbuild_plugin
open Command
 
let () =
  dispatch begin function
  | After_rules ->
     ocaml_lib ~extern:true ~dir:"+lablGL" "lablgl";
     ocaml_lib ~extern:true ~dir:"+lablGL" "lablglut";
  | _ -> ()
  end

The ocaml_lib declarations are the important part of this plugin. You can reach some documentation about this function in the API documentation. This declaration inform ocamlbuild and produce tags to use the library, they are named use_<library_name>.

Note that the order of ocaml_lib calls determine the order in which they are linked by the C compiler. In the above example, if tag use_lablgl and use_lablglut are both used, ocamlc and ocamlopt are linked first with -llalblgl, then with -llalblglut.

Then you have to specify programs which use these libraries, you can do so using the _tags file.

$ cat _tags
# Tag things that are linked with external libraries
<main.{byte,native}>: use_lablgl, use_lablglut
# Tag also sources that use these libraries.
# This will add -I +lablGL.
# You can specify something more precise than **/*.ml
<**/*.ml>: use_lablgl
$ ocamlbuild main.byte main.native

That's it!

Note: that's also the case when Using internal libraries.