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=0.0 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 mail4-relais-sop.national.inria.fr (mail4-relais-sop.national.inria.fr [192.134.164.105]) by yquem.inria.fr (Postfix) with ESMTP id 32D61BC6B for ; Sun, 10 Feb 2008 23:05:26 +0100 (CET) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AgAAAJ4Dr0fAXQInh2dsb2JhbACQOwEBAQgKKZU+ X-IronPort-AV: E=Sophos;i="4.25,331,1199660400"; d="scan'208";a="22450839" Received: from concorde.inria.fr ([192.93.2.39]) by mail4-smtp-sop.national.inria.fr with ESMTP; 10 Feb 2008 23:05:25 +0100 Received: from mail1-relais-roc.national.inria.fr (mail1-relais-roc.national.inria.fr [192.134.164.82]) by concorde.inria.fr (8.13.6/8.13.6) with ESMTP id m1AM5PFZ009274 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=OK) for ; Sun, 10 Feb 2008 23:05:25 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AgAAAGQEr0fBMVMPh2dsb2JhbACQOwEBAQgKKZU7 X-IronPort-AV: E=Sophos;i="4.25,331,1199660400"; d="scan'208";a="7878181" Received: from kabis.univ-orleans.fr (HELO ka.univ-orleans.fr) ([193.49.83.15]) by mail1-smtp-roc.national.inria.fr with ESMTP; 10 Feb 2008 23:05:25 +0100 Received: from smtps.univ-orleans.fr (localhost [127.0.0.1]) by ka.univ-orleans.fr (Postfix) with ESMTP id C0D4812B0BE; Sun, 10 Feb 2008 23:05:24 +0100 (CET) Received: from [192.168.0.12] (ras75-4-82-235-58-110.fbx.proxad.net [82.235.58.110]) by smtps.univ-orleans.fr (Postfix) with ESMTP id 0D84736E5B; Sun, 10 Feb 2008 23:05:29 +0100 (CET) Subject: Re: [Caml-list] [OSR] Exceptionless error management, take 2 From: David Teller To: yminsky@gmail.com Cc: OCaml In-Reply-To: <891bd3390802101047o187a94fch8f66a6c8a457d391@mail.gmail.com> References: <1202396482.6084.5.camel@Blefuscu> <891bd3390802101047o187a94fch8f66a6c8a457d391@mail.gmail.com> Content-Type: text/plain Date: Sun, 10 Feb 2008 23:05:23 +0100 Message-Id: <1202681123.6278.40.camel@Blefuscu> Mime-Version: 1.0 X-Mailer: Evolution 2.12.1 Content-Transfer-Encoding: 7bit X-Miltered: at concorde with ID 47AF7525.000 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)! X-Spam: no; 0.00; univ-orleans:01 yaron:01 minsky:01 monadic:01 monadic:01 univ-orleans:01 lifo:01 lifo:01 nomenclature:01 pipelines:01 ocaml:01 cheers:01 liquidations:98 wrote:01 unix:01 On Sun, 2008-02-10 at 13:47 -0500, Yaron Minsky wrote: > A couple of quick thoughts about the proposal: > * I don't understand the motivation behind separating out > may_fail and status. In the case where no explicit error is > returned, we're happy to return an ordinary option. Why not > return a status when we want to return an error condition? And > I don't understand the argument about wanting to delay > evaluation until the function result is called. Why is that > good, and if it's good, why do we still support functions that > return options? The whole thing seems to add verbosity with > little gain. I agree that this is the most arguable part of this recommendation candidate. I introduced it because * it makes possible to decide at a later stage between several mechanisms for delivering errors from within libraries * some of these mechanisms make possible to use fully monadic exceptionless error management, without the usual high cost of fully monadic exceptionless error management I have put together three different implementations for such mechanisms [1] and an example of fully monadic exceptionless error management [2]. [1] http://www.univ-orleans.fr/lifo/Members/David.Teller/software/exceptionless/exceptionless.ml [2] http://www.univ-orleans.fr/lifo/Members/David.Teller/software/exceptionless/test_monad.ml * * > * I think some attention on nomenclature is in order. In the > libraries Jane Street uses, we have something similar to > status (called "result"), but the type is "Ok of 'a | Error of > 'b" rather than "Success of 'a | Error of 'b", simply for > terseness. Also, having a function called "result" which > converts a "may_fail" into a "status" seems like one name too > many. I would call both the function and the type the same > thing (either status or result). Unless, of course, you want > to imply something material about the operation, in which case > calling it "eval" or somesuch would make sense. Interesting question. You are correct that "eval" might make more sense and I believe nobody would object to "Ok|Error" instead of "Success| Error". If terseness is a concern, "Bad" might even make a shorter replacement for "Error", although this would probably be harder to read. > * I don't understand why this proposal is only for functional > data types. I didn't find the motivation given in the OSR for > this convincing. I feel like the use of exceptions involves > roughly the same tradeoffs when you're using imperative and > functional code. If you have long functional pipelines, doing > exception handling at each stage is a pain, much as it is if > you do long sequences of imperative operations. That's why I > think the goal should not be for the interfaces to be > "exceptionless" so much as to make it easier to keep track of > where exceptions might and might not be thrown, so that the > reader of a piece of code knows where to stop and worry about > exceptions. My intuition is that managing errors with ('a, 'b) status (or whatever this name may become) is mostly functional in the first place. I have in mind functions such as Unix.rename, which return nothing but may fail. Without exceptions, one would need to stop at each step to check if no error has occurred. Of course, we can handle this with monadic operators, just as we would handle errors in functional code. I believe this monadic approach is as close as we can get to having errors tracked by the type system without requiring the user to handle them at each step along the road. Now, I admit that I usually write functional code, so input from people dealing in imperative code in OCaml would be interesting. > y Cheers, David -- David Teller Security of Distributed Systems http://www.univ-orleans.fr/lifo/Members/David.Teller Angry researcher: French Universities need reforms, but the LRU act brings liquidations.