From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <serge@hq.idt.net>
X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr
X-Spam-Level: 
X-Spam-Status: No, score=0.0 required=5.0 tests=none autolearn=disabled 
	version=3.1.3
X-Original-To: caml-list@yquem.inria.fr
Delivered-To: caml-list@yquem.inria.fr
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39])
	by yquem.inria.fr (Postfix) with ESMTP id 563C2BC69
	for <caml-list@yquem.inria.fr>; Wed, 28 Mar 2007 14:37:57 +0200 (CEST)
Received: from mta5.srv.hcvlny.cv.net (mta5.srv.hcvlny.cv.net [167.206.4.200])
	by concorde.inria.fr (8.13.6/8.13.6) with ESMTP id l2SCbu6P000951
	for <caml-list@inria.fr>; Wed, 28 Mar 2007 14:37:57 +0200
Received: from [192.168.15.101]
 (ool-457da870.dyn.optonline.net [69.125.168.112]) by mta5.srv.hcvlny.cv.net
 (Sun Java System Messaging Server 6.2-6.01 (built Apr  3 2006))
 with ESMTP id <0JFM00FWA5R7N5C0@mta5.srv.hcvlny.cv.net> for
 caml-list@inria.fr; Wed, 28 Mar 2007 08:37:56 -0400 (EDT)
Date: Wed, 28 Mar 2007 08:40:50 -0500
From: Serge Aleynikov <serge@hq.idt.net>
Subject: Re: [Caml-list] Wrapping OCaml function returning a variant
In-reply-to: <CDE554C6-8389-45AD-A72C-091CD75C88C0@gmail.com>
To: Joel Reymont <joelr1@gmail.com>
Cc: Caml List <caml-list@inria.fr>
Message-id: <460A7062.7050609@hq.idt.net>
MIME-version: 1.0
Content-type: text/plain; charset=ISO-8859-1; format=flowed
Content-transfer-encoding: 7BIT
References: <E888843F-390B-49FB-82E5-662088922B56@gmail.com>
 <460A65AB.8020902@hq.idt.net> <CDE554C6-8389-45AD-A72C-091CD75C88C0@gmail.com>
User-Agent: Thunderbird 1.5.0.10 (Windows/20070221)
X-Miltered: at concorde with ID 460A61A4.000 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)!
X-Spam: no; 0.00; ocaml:01 c-interface:01 variants:01 syntax:01 foo:01 syntax:01 variants:01 constructors:01 ocaml:01 toplevel:01 camlp:01 foo:01 val:01 constructors:01 val:01 

Joel Reymont wrote:
> 
> On Mar 28, 2007, at 1:55 PM, Serge Aleynikov wrote:
> 
>> You can read the section 18.3.4 of 
>> http://caml.inria.fr/pub/docs/manual-ocaml/manual032.html
> 
> It does not clearly explain how to handle variant types in C code. Maybe 
> I'm dumb but I did not understand it.
> 
>> Then if still unclear, examine: http://oracaml.sourceforge.net/
>> or any other C-interface library available on Caml Hump: 
>> http://caml.inria.fr/cgi-bin/hump.en.cgi?sort=0&browse=65
> 
> It looks like you are using polymorphic variants in new syntax. Maybe 
> I'm wrong but it doesn't work for me
> 
> # type foo = [Null | Int of int];;
> Syntax error

That's because this code is written using revised 
(http://caml.inria.fr/pub/docs/tutorial-camlp4/tutorial005.html) syntax. 
  These are not polymorphic variants but rather a basic union type with 
non-constant constructors.

Hint: you can start the ocaml toplevel like this to get it understand 
revised syntax: "ocaml camlp4r.cma".

 > I still don't understand how I can handle regular variants of the
 > following type returned by OCaml to the C side

In terms of your example above, on the C side you would do:

void bar(value foo) {
   if (Is_long(foo)) {
      switch (Long_val(foo)) {
        case 0: /* Null */
          ...
          break;
        /* if there are other constant constructors besides Null
           add additional cases here */
        default:
          fail_exception(Long_val(foo), "Unknown constant constructor!");
      }
   } else {
      switch (Tag_val(foo)) {
        case 0:  /* Int of int */
          /* Access the non-constant value by Long_val(Field(foo,0))) */
          break;
        ...
      }
   }
}

Regards,

Serge