From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr X-Spam-Level: X-Spam-Status: No, score=0.4 required=5.0 tests=AWL,DNS_FROM_RFC_ABUSE autolearn=disabled version=3.1.3 X-Original-To: caml-list@yquem.inria.fr Delivered-To: caml-list@yquem.inria.fr Received: from mail4-relais-sop.national.inria.fr (mail4-relais-sop.national.inria.fr [192.134.164.105]) by yquem.inria.fr (Postfix) with ESMTP id CD0C4BB84 for ; Thu, 17 Jul 2008 02:43:53 +0200 (CEST) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ApoEAHMyfkiCNhAB/2dsb2JhbACwYQ X-IronPort-AV: E=Sophos;i="4.31,199,1215381600"; d="scan'208";a="27394860" Received: from kurims.kurims.kyoto-u.ac.jp ([130.54.16.1]) by mail4-smtp-sop.national.inria.fr with ESMTP; 17 Jul 2008 02:43:52 +0200 Received: from localhost (orion [130.54.16.5]) by kurims.kurims.kyoto-u.ac.jp (8.13.8/8.13.8) with ESMTP id m6H0hP1r009878; Thu, 17 Jul 2008 09:43:25 +0900 (JST) Date: Thu, 17 Jul 2008 09:43:28 +0900 (JST) Message-Id: <20080717.094328.191385811.garrigue@math.nagoya-u.ac.jp> To: jeremy.yallop@ed.ac.uk Cc: darioteixeira@yahoo.com, caml-list@yquem.inria.fr Subject: Re: [Caml-list] Troublesome nodes From: Jacques Garrigue In-Reply-To: <487BAB0B.6030000@ed.ac.uk> References: <831.74975.qm@web54604.mail.re2.yahoo.com> <487BAB0B.6030000@ed.ac.uk> X-Mailer: Mew version 5.2 on Emacs 22.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Spam: no; 0.00; nodes:01 node:01 generative:01 datatypes:01 generative:01 wrote:01 abstract:01 abstract:01 defines:01 caml-list:01 constraint:01 implemented:02 garrigue:03 garrigue:03 jacques:03 From: Jeremy Yallop > Dario Teixeira wrote: > > type ('a, 'b) t = private 'a constraint 'a = [< super_node_t ] > > I don't think this is quite what you want yet, although it's getting > close! > > The first problem is that phantom types must be implemented in terms > of abstract (or at least generative) types. This is actually the other way round: abstract and private types allow phantom types, but abbreviations and normal datatypes (generative ones) don't. So the above code really defines a phantom type. Jacques Garrigue