Creating an OCaml library
ocaml, ocamlbuild
Solution
OCamlbuild has some built-in functionality for building libraries, so you can get started with just `ocamlbuild foo.cma foo.cmxa` (assuming `foo.ml` is your entry point). This will invoke `ocamlopt -a` and `ocamlc -a` for you, handling all the dependency plumbing and leaving the generated files inside `_build`.
That should be enough to let you compile a library and link it from another program. Since this is just a test you can simply point at the aforementioned `_build` with `-I` when compiling the program that uses the library. For real use a library should be packaged - when you get to that point you'll want to look into ocamlfind, oasis, etc.
Have a look at the ocaml.org tutorial on compiling OCaml projects. Additionally the official manual for the bytecode and native code compilers contains useful detail on producing and using the various types of files.
Problem
I am trying to create a library that I can use in other OCaml projects, and I'm totally lost. I'm currently using `ocamlbuild` which is great for spitting out executables, but I don't know how to get a library out of it. I've discovered the -a option in `ocamlopt` and `ocamlc` but I'm not really sure how to use it. The documentation I've found (for example, here), seems to assume some preexisting knowledge. I don't even know what a .a file is. After I run that, which of the outputted files do I need to build a project that depends on this library? Do I need the mli files so that the application knows the signatures of the library code, or is that included in the output somehow? Also, it would be nice to be able to package all the files together, something similar to a .jar file for Java. In any case, I would love for `ocamlbuild` to do all of this for me, since if I have to invoke `ocamlopt -a` I will have to either manually specify dependencies or hack a script around `ocamldep` -- something that `ocamlbuild` was supposed to fix. However, I don't know how to tell it to build a library. I'm willing to use oasis or OPAM or something if it's necessary, but I would like to learn how to do this using just the basic tools first.