Re: [Caml-list] Callback.register equivalent before runtime is

[Evgeny Roubinchtein <evgenyr@cs.ubc.ca>]

On Thu, Aug 22, 2013 at 05:47:56AM -0000, oleg@okmij.org wrote:
> 
> > I am learning about run-time compilation, and using OCaml as a base for
> > my experiments.  So far, I have a really simple C primitive that just
> 
> > However, I am now trying to move to producing bytecode executables, so,
> > if I stay with my current set-up I would need to do the equivalent of
> > Callback.register (i.e., put the address of the wrapper into the hash
> > table maintained by caml_callback_register) before any of the "user
> > code" in the executable starts to run. 
> 
> You may want to look into how MetaOCaml does it. Briefly, you just
> have to link in your own .cmo file right before user's files. Your
> file will set things up. For example, metaocamlc is a shell script
> that does 
> 
>      exec ocamlc -I +compiler-libs ocamlcommon.cma ocamlbytecomp.cma ocamltoplevel.cma metalib.cma berstart.cmo "$@"
> 
> The key is the file berstart.cmo placed before any user files to
> compile and link. That file is trivial and enclosed for
> convenience. The file mentions Toplevel because MetaOCaml relies on
> top-level for executing code created at run-time. You can add your
> registration code to that file.
> 
> (*
>    To `run' the code we use toplevel facilities.
>    If we invoke BER MetaOcaml top level, then Toplevel.topstart() will
>    initalialize the top level.
>    If we execute a byte-compiled executable, we link with
>    the top-level library. But we need initialize it first.
>    This is the job of the current file.
> 
>    This file must be linked in *before* the first user executable.
> 
>    The present code roughly do the same steps OCaml top level does
>    when executing a script.
>    See Toplevel.topmain
> *)
> 
> let () =
>   Toploop.set_paths ();
>   Compile.init_path();
>   Toploop.initialize_toplevel_env ()

Thank you.  Yes, after experimenting with David Allsop's earlier
suggestion, I eventually realized that "module initialization" code gets
executed "early enough for my purposes", so I ended up doing exactly
what you suggested above.

-- 
Best,
Evgeny