220 21618 article Path: news.gmane.org!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: is await an extension of the do-notation? (was Re: Re: Resumable expressions p0114r0 vs async/await P0057R0) Date: Mon, 12 Oct 2015 12:59:26 -0700 Lines: 169 Approved: news@gmane.org Message-ID: References: <639f0012-8cb4-4db3-82a6-8d042a3497f9@isocpp.org> <401aa118-ed0b-4c7b-92cf-3fbd706eff9d@isocpp.org> <1d15dbc4-e0c1-4df1-86db-014e11f14d26@isocpp.org> <56114953.4030701@wanadoo.fr> <561B403D.4030403@gmail.com> <561C07D1.3080304@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a114391283726880521edc412 X-Trace: ger.gmane.org 1444679978 10261 80.91.229.3 (12 Oct 2015 19:59:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 12 Oct 2015 19:59:38 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBDVNBJG4YAIBBHVC6CYAKGQECLWL35Y@isocpp.org Mon Oct 12 21:59:36 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZljFp-00015X-Bu for gclcip-std-proposals@m.gmane.org; Mon, 12 Oct 2015 21:59:29 +0200 Original-Received: by ioae62 with SMTP id e62sf40447432ioa.2 for ; Mon, 12 Oct 2015 12:59:28 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=F9nIUez7wVo4jT/9VlGlQ38LxBwUFch8dxbkAFjN8ac=; b=E9CdqzyTc/kfL8JaOA8NwsZc8pNJd+6zTg5hhQb/NHY9Nu19LGOjXeFimr3oeRVBFK jxBWBY3eUMaIBhKgvjFVJn76r5MitjmYN+unG2Ma6J+WxckyHdiVBW7bwshHH9iNZiqp N1JysK0dO2Nf5DPUcp+bLuwABi/ilgGsKcRbGwszaEPQeh19/TMWR1Yk/rMEcKZJ6zZy NSZ4zXHZj+y5tdVZZOzq02zfsC8wYnTtExP2LnU55BAqbVqt65cX34Nk+jnGgMhMRyub zE690HA3ku0nobWYXzq0iEMH8DfgntsWdKzUBbhJ3lKXxuF+/PcwqzXG87Y+Qf+UzWJ+ +HzA== X-Gm-Message-State: ALoCoQmpSGkmtV+1ZXXcjT+qnagp0JKMpVoQ0KaEA1XLRVj5okTVT3U3t0HC/VgP3/Tyy47tYkPZ X-Received: by 10.182.215.226 with SMTP id ol2mr25925829obc.11.1444679968653; Mon, 12 Oct 2015 12:59:28 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.23.42 with SMTP id 39ls2682053qgo.70.gmail; Mon, 12 Oct 2015 12:59:26 -0700 (PDT) X-Received: by 10.31.194.2 with SMTP id s2mr17862215vkf.39.1444679966694; Mon, 12 Oct 2015 12:59:26 -0700 (PDT) Original-Received: from mail-vk0-x22b.google.com (mail-vk0-x22b.google.com. [2607:f8b0:400c:c05::22b]) by mx.google.com with ESMTPS id f40si1787127vki.4.2015.10.12.12.59.26 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Oct 2015 12:59:26 -0700 (PDT) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c05::22b as permitted sender) client-ip=2607:f8b0:400c:c05::22b; Original-Received: by vkgc187 with SMTP id c187so28541475vkg.3 for ; Mon, 12 Oct 2015 12:59:26 -0700 (PDT) X-Received: by 10.31.54.83 with SMTP id d80mr19153685vka.88.1444679966464; Mon, 12 Oct 2015 12:59:26 -0700 (PDT) Original-Sender: metafoo@gmail.com Original-Received: by 10.31.142.72 with HTTP; Mon, 12 Oct 2015 12:59:26 -0700 (PDT) In-Reply-To: X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c05::22b as permitted sender) smtp.mailfrom=metafoo@gmail.com; dkim=pass header.i=@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:21618 Archived-At: --001a114391283726880521edc412 Content-Type: text/plain; charset=UTF-8 On Mon, Oct 12, 2015 at 12:30 PM, Gor Nishanov wrote: > Evgeny: > > Note the "purity" word in Richard's answer. > If you write a body of the coroutine in a pure manner, you can hack P0057 > and in your await_suspend for the list monad resume the coroutine multiple > times. > You need to provide proper final_suspend and return_value to make it work. > But it will work ONLY if your body is pure :-). That is the body of your > coroutine. And you cannot save any state in the awaiter, since it is torn > down at the end of the full expressions, hence, I am using thread_local to > ferry a value from await_suspend to await_resume. > > Here is "do not try this at home" awaiter for the list. Untested. Just > an idea of how it can look like. > > auto operator await(list const& l) { > struct awaiter { > list const * list_; > > static thread_local T* result_; > > bool await_ready() { return false; } > > void await_suspend(coroutine_handle<> h) { > auto l = list_; > for (auto && item : *l) { result_ = &item; h.resume(); } > For this to work, I think you'd need your coroutine to (somehow) repeatedly await the list item. That is, instead of: list_monad foo(list_monad v) { int x = await v; return x * x; } .... you'd need to write: list_monad foo(list_monad v) { loop: int x = await v; // somehow return x * x then conditionally goto loop. } .... because you don't have any kind of call/cc primitive. -- --- 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 email 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-proposals/. --001a114391283726880521edc412 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On M= on, Oct 12, 2015 at 12:30 PM, Gor Nishanov <gornishanov@gmail.com&= gt; wrote:
Evgeny:

Note the "purity" word in Richard's answer.
= If you write a body of the coroutine in a pure manner, you can hack P0057 a= nd in your await_suspend for the list monad resume the coroutine multiple t= imes.
You need to provide proper final_suspend and return_value t= o make it work. But it will work ONLY if your body is pure :-). That is the= body of your coroutine. And you cannot save any state in the awaiter, sinc= e it is torn down at the end of the full expressions, hence, I am using thr= ead_local to ferry a value from await_suspend to await_resume.
Here is "do not try this at home" awaiter for the li= st<T>. Untested. Just an idea of how it can look like.

=
auto operator aw= ait(list<T= > const& l) {
=C2=A0 struct awaiter {
=C2=A0 =C2=A0 list<T> const * list_;

=C2=A0 =C2=A0 static = thread_local T* result_;

=C2=A0 =C2=A0 bool await_ready() { return false;<= span style=3D"color:rgb(0,0,0)"> }

=C2=A0 =C2=A0 void await_suspend(coroutine_handle<> h) {
=C2=A0 =C2=A0 =C2=A0 =C2=A0auto l =3D list_;
=C2=A0 =C2=A0 =C2=A0 =C2=A0for (auto = && item : = *l) { result_ =3D &item;= h.resume(); = }

For this to work, I think you'= ;d need your coroutine to (somehow) repeatedly await the list item. That is= , instead of:

list_monad<int> foo(list_monad= <int> v) {
=C2=A0 int x =3D await v;
=C2=A0 retur= n x * x;
}

... you'd need to write:<= /div>

list_monad<int> foo(list_monad<int&g= t; v) {
loop:
=C2=A0 int x =3D await v;
=C2= =A0 // somehow return x * x then conditionally goto loop.
}
=

... because you don't have any kind of call/c= c primitive.

--

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