220 31309 <5d94e416-e8bf-41e1-98f3-eee6133c9b64@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Giovanni Piero Deretta Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: P0534: call/cc, type safety and exceptions Date: Thu, 2 Mar 2017 03:29:34 -0800 (PST) Lines: 115 Approved: news@gmane.org Message-ID: <5d94e416-e8bf-41e1-98f3-eee6133c9b64@isocpp.org> References: <3a57e294-7254-4358-828d-c9f7757f5295@isocpp.org> <4e6c13b2-4286-4df8-989b-97cbf3bf1cc7@isocpp.org> <312d04a6-8b20-4bf5-8357-507ba9938e84@isocpp.org> <762243ed-0c31-461d-b6fd-fdb8759857b2@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_118_329297088.1488454174790" X-Trace: blaine.gmane.org 1488454178 2317 195.159.176.226 (2 Mar 2017 11:29:38 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 2 Mar 2017 11:29:38 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDEP3I7TGEIJ7BHAYUCRUBADL3TXW@isocpp.org Thu Mar 02 12:29:33 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f199.google.com ([209.85.161.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cjOvK-00088W-9a for gclcip-std-proposals@m.gmane.org; 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Thu, 02 Mar 2017 03:29:36 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.32.34 with SMTP id n31ls5845952ota.4.gmail; Thu, 02 Mar 2017 03:29:35 -0800 (PST) X-Received: by 10.157.32.161 with SMTP id x30mr1519939ota.20.1488454175423; Thu, 02 Mar 2017 03:29:35 -0800 (PST) In-Reply-To: X-Original-Sender: gpderetta@gmail.com 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:31309 Archived-At: ------=_Part_118_329297088.1488454174790 Content-Type: multipart/alternative; boundary="----=_Part_119_1951193406.1488454174790" ------=_Part_119_1951193406.1488454174790 Content-Type: text/plain; charset=UTF-8 On Thursday, March 2, 2017 at 11:09:49 AM UTC, Oliver Kowalke wrote: > > 2017-03-02 11:52 GMT+01:00 Giovanni Piero Deretta >: > >> >> [1] contrary to what P0534 claims, it describes delimited continuations; >> I'm not even sure you can have undelimited continuations when you have >> one-shot semantics. >> > > undelimited continuations == no delimiter that tells you where the > continuatio nends, e.g. if you call callcc() from main(), it is undelimited > there are a whole family of delimited continuations semantics each with slightly different delimiter/invoker semantics. shift/reset is just one of them. With undelimted continuation you can return from call/cc and fall back in the original continuation, while still holding the captured continuation, allowing returning 'twice'. This is of course not possible with oneshot continuation, and callcc (and yield), in a way, do inserts a prompt. Now, if I understand correctly, with shift/reset, shift finds the closest dynamically scoped reset in the callstack, while with callcc and yield, there is not a clear distinction between the prompt and the shift point as they are both continuations and they are statically scoped (on the other hand, asymmetric coroutines with an explicit thread local parent pointer more closely match shift/reset model). Regarding main, the continuation is implicitly delimited as you can't fall further than that and return to the os instead. Oleg Kiselyov (which has done a lot of work on the topic) in fact claims that undelimited continuations do not really exist, as a delimiter always exists, it might just be outside of the programmer control. Anyway, I don't pretend to understand fully the formal semantics of continuations, so I might be mistaken. It doesn't really matter that much for us C++ programmers though . -- gpd -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/5d94e416-e8bf-41e1-98f3-eee6133c9b64%40isocpp.org. ------=_Part_119_1951193406.1488454174790 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Thursday, March 2, 2017 at 11:09:49 AM UTC, Oliver Kowa= lke wrote:
2017-03-02 11:52 GMT+01:00 Giovanni Piero Dere= tta <gpde...@gmail.com>:

[1] contrary to what= P0534 claims, it describes delimited continuations; I'm not even sure = you can have undelimited continuations when you have one-shot semantics.

undelimited continuations = =3D=3D no delimiter that tells you where the continuatio nends, e.g. if you= call callcc() from main(), it is undelimited
=

there are a whole family of delimited continuations semantics each= with slightly different delimiter/invoker semantics. shift/reset is just o= ne of them.

With undelimted continuation you can return from call/c= c and fall back in the original continuation, while still holding the captu= red continuation, allowing returning 'twice'. This is of course not= possible with oneshot continuation, and callcc (and yield), in a way, do i= nserts a prompt. Now, if I understand correctly, with shift/reset, shift fi= nds the closest dynamically scoped reset in the callstack, while with callc= c and yield, there is not a clear distinction between the prompt and the sh= ift point as they are both continuations and they are statically scoped (on= the other hand, asymmetric coroutines with an explicit thread local parent= pointer more closely match shift/reset model).

Regarding main, the = continuation is implicitly delimited as you can't fall further than tha= t and return to the os instead. Oleg Kiselyov (which has done a lot of work= on the topic) in fact claims that undelimited continuations do not really = exist, as a delimiter always exists, it might just be outside of the progra= mmer control.

Anyway, I don't pretend to understand fully the fo= rmal semantics of continuations, so I might be mistaken. It doesn't rea= lly matter that much for us C++ programmers though .

-- gpd

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