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Date: 22 Aug 2013 05:47:56 -0000
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From: oleg@okmij.org
To: evgenyr@cs.ubc.ca
CC: caml-list@inria.fr
In-reply-to: <20130815070432.GA31041@jade.home.test>
Subject: Re: [Caml-list] Callback.register equivalent before runtime is


> 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 ()