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[Caml-list] embedding Ocaml in an existing application
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Date: 2001-12-07 (14:40)
From: Basile STARYNKEVITCH <basile@s...>
Subject: [Caml-list] embedding Ocaml in an existing application

Some remarks (and wishes) about embedding Ocaml (bytecoded) in an
existing application.

I just embedded (a single day hack) Ocaml inside the Larbin web
crawler (coded in C++ by Sebastien Ailleret) on
http://pauillac.inria.fr/~ailleret/prog/larbin/ You should be able to
get the patch from my personal web page or else email me either at
work <basile.starynkevitch@cea.fr> or at home
<basile@starynkevitch.net>. This because I need (for the POESIA
project) to scan some part of the Web and get some crude measures of
features like: percentage of Web pages using Javascript (about 50%)
and mean length of such scripts (about 2Kbytes). So I hacked larbin to
add Ocaml inside it.

I used ocaml v3.02 or v3.01 (bytecode interpreter).

First remark: the ocaml linking mechanism use the undocumented -p
flag to dump all the Ocaml symbol table. So I had to hack Larbin's
main routine to test for the special -p single argument and then call
only ocaml_main_init(argv); and exit(0) in that case. I believe that
it would be quite trickly to embed Ocaml inside a significant
application which uses the -p flag (see the code in
ocaml/byterun/startup.c routine parse_command_line). At least I
suggest that the linking mechanism use a less natural convention (such
as "-print-ocaml-symbols" as argv[1] of main) and that it could be
documented. (and I did not found quickly where Ocaml invokes this
magic -p flag).

Second remark: for embedding Ocaml inside Larbin I need the
-use-runtime flag to the ocamlc compiler. But it seems that the next
version (v3.03) does not have it anymore. I hope that it will still be
possible to embed OCaml inside an application without having to
compile the whole application as a shared library.

3rd remark: 
why don't caml_main take and changes the main argc,argv arguments
(like e.g. gtk_init routine in the Gtk toolkit) so that the
application can use the other arguments. Otherwise, I suggest to
publicize the parse_command_line routine so an embedding application
could parse its own main arguments and pass some others to ocaml
before starting the Ocaml interpreter. (imagine you want to embed
Ocaml inside an existing Gtk application?).

My previous post http://caml.inria.fr/archives/200112/msg00015.html
regarding a tiny syntactic extension was related to this [Larbin]
patch. I think that novice Ocaml users might be interested in a
syntactic sugar to register bound values.

Regards to all

Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
email: basile<at>starynkevitch<dot>net 
alias: basile<at>tunes<dot>org 
8, rue de la Faïencerie, 92340 Bourg La Reine, France
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