220 11044 <538777A8.4050706@hyc.io> article Path: news.gmane.org!not-for-mail From: Pierre Talbot Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: N4015: A proposal to add a utility class to represent expected monad Date: Thu, 29 May 2014 20:08:40 +0200 Lines: 71 Approved: news@gmane.org Message-ID: <538777A8.4050706@hyc.io> References: <94ded66f-1c50-47b9-8a04-b83805443da9@isocpp.org> <1534916.IcxgtEDE2B@drako> <5384FDF2.6060904@hyc.io> <2524692.K0qNjsgtn9@drako> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1401809573 27831 80.91.229.3 (3 Jun 2014 15:32:53 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 3 Jun 2014 15:32:53 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH7J5FDT4ERBH6VW6OAKGQEHLGLONQ@isocpp.org Tue Jun 03 17:32:48 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f198.google.com ([209.85.217.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Wrqhj-0005Ac-Oq for gclcip-std-proposals@m.gmane.org; Tue, 03 Jun 2014 17:32:47 +0200 Original-Received: by mail-lb0-f198.google.com with SMTP id l4sf4019296lbv.5 for ; Tue, 03 Jun 2014 08:32:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :subject:references:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type:content-transfer-encoding; bh=R31LkZwuPdPu1++Gi+Z4Q6NF5o26ucUL+IkJidut5Oc=; b=au5Tya9VaPGWspJohvQvVSyguOH7ISNzmCtrR+eHL7WoH3h7vnBlw0tLt3NnRXVqB/ FwR1JWgMNZ2VmQ54Mtv9Ol6GnFy2ufU+QPnaAybQDadPEYPwxpZNQXyoBPn/6gZlHHYe mrukA1JPWpZNyTTonwZtGNH53cMm/RWz2twTTO46lB7DZUhuQNCOg06Hnp+vlMtP9sWd PhWuHa2nwnGuNjbMK+RAxQTkc3rDRneu/dGFRD3YyvOzGOPdJnYDg6yEibys6X7kv+oq W3VcH2yKkdJLs7G8aAFRc9v1aKj/5SX2F/Bzw32apteWaqs3Ionb3AT4Vj0DiqhqipqD OFW X-Gm-Message-State: ALoCoQmxytOUUsSST7okJW7Z/qqA2kNwyGOIWIUGQPCAPUvRw3xb7I+KBcxVR0obyUh9tWiTkmuX X-Received: by 10.152.29.169 with SMTP id l9mr3886671lah.3.1401809567449; Tue, 03 Jun 2014 08:32:47 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.36.39 with SMTP id n7ls449849laj.80.gmail; Tue, 03 Jun 2014 08:32:46 -0700 (PDT) X-Received: by 10.112.137.138 with SMTP id qi10mr3970006lbb.4.1401809566545; Tue, 03 Jun 2014 08:32:46 -0700 (PDT) Original-Received: by 10.194.100.38 with SMTP id ev6mswjb; Thu, 29 May 2014 11:09:06 -0700 (PDT) X-Received: by 10.180.107.130 with SMTP id hc2mr49001273wib.7.1401386946528; Thu, 29 May 2014 11:09:06 -0700 (PDT) Original-Received: from xvm-161-161.ghst.net ([2001:4b98:dc0:47:216:3eff:fe48:3630]) by mx.google.com with ESMTPS id mz5si22246332wic.67.2014.05.29.11.08.58 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 29 May 2014 11:08:58 -0700 (PDT) Received-SPF: none (google.com: ptalbot@hyc.io does not designate permitted sender hosts) client-ip=2001:4b98:dc0:47:216:3eff:fe48:3630; Original-Received: from [192.168.1.17] (nsg93-8-88-175-59-164.fbx.proxad.net [88.175.59.164]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by xvm-161-161.ghst.net (Postfix) with ESMTPSA id 3F8C72C0CF for ; Thu, 29 May 2014 20:08:40 +0200 (CEST) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 In-Reply-To: <2524692.K0qNjsgtn9@drako> X-Original-Sender: ptalbot@hyc.io X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: ptalbot@hyc.io does not designate permitted sender hosts) smtp.mail=ptalbot@hyc.io Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:11044 Archived-At: On 05/28/2014 11:10 PM, Ivan =C4=8Cuki=C4=87 wrote: > Hi Pierre, > >> First of all, thank you for the feedback. > Thank you for the proposal - I'd love to see a few more functional parts = like > this in STL. > >> std::exception_ptr being the default type for E might not be a good >> idea. Exceptions are a way to handle error but expected is another. The > Well, integer error codes vs typed errors... I guess we could start a hol= y war > over this :) IMHO, typed errors are only useful when there is contextual information=20 to report along with the error. Otherwise integer error codes do the job=20 well. Exception are only a kind of "typed error" and I'd advise to use a=20 custom error structure (with virtual methods) over exceptions since we=20 cannot add virtual method to the existing std::exception type. Another=20 possibility would be to use a variant but it has the=20 inconvenient to change the signature if a new error is added. Using exceptions when we don't need to interface with code using=20 exception is bad, it means we use the try-catch mechanism to go through=20 a hierarchy, this is not the goal of try-catch. > >> This is true, however in practice I suspect that users will use a type >> definition on expected with their own error type: >> >> template >> using expectation =3D expected; >> >> We get back our "happy path" :-) > Yes, I guess that will become a new common idiom. Honestly, I'm not overl= y > happy about STL things needing a typedef/using to make them useful, but y= es, > this would be ok. > >> IMHO, we didn't use fancy names neither we invented any :-) map and bind > I agree map/fmap/bind are already established names, but outside of C++. = This > remark was not aimed for this proposal per se, but more of a general worr= y > that we started introducing monads into C++ without predefining the commo= n > terminology. > >> Note that we add a syntax for a do-notation like in the section 7.1. > Yes, saw that. That is one of the things I'd put in a separate proposal -= I'm > guessing it will receive more resistance than just the expected<...> temp= late. I'm totally agree with you, this has little to do in the expected=20 proposal. We put it in because we wanted people to see aesthetic ways of=20 manipulating expected and monads in general. Cheers, Pierre --=20 ---=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. .