From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <rich@annexia.org>
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=AWL autolearn=disabled 
	version=3.1.3
X-Original-To: caml-list@yquem.inria.fr
Delivered-To: caml-list@yquem.inria.fr
Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104])
	by yquem.inria.fr (Postfix) with ESMTP id 2B515BBCA
	for <caml-list@yquem.inria.fr>; Tue, 18 Mar 2008 11:56:48 +0100 (CET)
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: ApoEAGM830fAXQIn/2dsb2JhbACpOA
X-IronPort-AV: E=Sophos;i="4.25,517,1199660400"; 
   d="scan'208";a="10396605"
Received: from concorde.inria.fr ([192.93.2.39])
  by mail3-smtp-sop.national.inria.fr with ESMTP; 18 Mar 2008 11:56:47 +0100
Received: from mail4-relais-sop.national.inria.fr (mail4-relais-sop.national.inria.fr [192.134.164.105])
	by concorde.inria.fr (8.13.6/8.13.6) with ESMTP id m2IAul4b004548
	(version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=OK)
	for <caml-list@inria.fr>; Tue, 18 Mar 2008 11:56:47 +0100
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: AqgBAOg830dQRFuwgGdsb2JhbACRAAEBCQqYLA
X-IronPort-AV: E=Sophos;i="4.25,517,1199660400"; 
   d="scan'208";a="23902379"
Received: from furbychan.cocan.org ([80.68.91.176])
  by mail4-smtp-sop.national.inria.fr with ESMTP; 18 Mar 2008 11:56:47 +0100
Received: from rich by furbychan.cocan.org with local (Exim 4.63)
	(envelope-from <rich@annexia.org>)
	id 1JbZUq-0006qc-6t
	for caml-list@inria.fr; Tue, 18 Mar 2008 10:56:44 +0000
Date: Tue, 18 Mar 2008 10:56:44 +0000
To: caml-list@inria.fr
Subject: Re: [Caml-list] Yet another question about insufficient polymorphism
Message-ID: <20080318105643.GA26219@annexia.org>
References: <20080312193431.GA10622@annexia.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20080312193431.GA10622@annexia.org>
User-Agent: Mutt/1.5.13 (2006-08-11)
From: Richard Jones <rich@annexia.org>
X-Miltered: at concorde with ID 47DF9FEF.000 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)!
X-Spam: no; 0.00; polymorphism:01 mli:01 val:01 val:01 mutable:01 bool:01 mutable:01 bool:01 casts:01 textbox:98 textbox:98 wrote:01 caml-list:01 unit:03 unit:03 

On Wed, Mar 12, 2008 at 07:34:32PM +0000, Richard Jones wrote:
> I have a signature like this:
> 
> newt.mli:
> 
>   type 'a component
> 
>   val form_add_component :
>     [> `Form ] component -> [> `Component ] component -> unit
>   val form_add_components :
>     [> `Form ] component -> [> `Component ] component list -> unit
> 
> An implementation like this:
> 
> newt.ml:
> 
>   type 'a component = {
>     co : newtComponent;
>     mutable in_form : bool;
>   }

[...]

> 04_form.ml:
> 
>   let text = textbox 1 1 15 5 [WRAP; SCROLL] in
>   textbox_set_text text "This is some text in a reflowed text box.";
>   let b1 = button 5 8 "  OK  " in
>   let b2 = button 5 13 "Cancel" in
>   let form = form None None [] in
>   form_add_components form [text; b1; b2];
>                                   ^^

The answer to this, pointed out to me by milanst, is to write the type
like this:

  type _component = {
    co : newtComponent;
    mutable in_form : bool;
  }
  type 'a component = _component

which works as expected, without any "casts" needed on the call to
form_add_components.

Rich.

-- 
Richard Jones
Red Hat