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Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Sum types visitation and future continuation similarities Date: Mon, 18 May 2015 21:04:36 +0200 Lines: 175 Approved: news@gmane.org Message-ID: <555A37C4.4070607@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------010703090002040307090707" X-Trace: ger.gmane.org 1431975452 3528 80.91.229.3 (18 May 2015 18:57:32 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 18 May 2015 18:57:32 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBDH67CONY4PBBD7M5CVAKGQEMKMIQMY@isocpp.org Mon May 18 20:57:23 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f200.google.com ([209.85.212.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YuQE5-0008Dv-BM for gclcip-std-proposals@m.gmane.org; Mon, 18 May 2015 20:57:21 +0200 Original-Received: by wivs14 with SMTP id s14sf26667286wiv.1 for ; Mon, 18 May 2015 11:57:20 -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:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=pT/PRTAi2VJe74dfPxqjZxDzXTtVj9OdDGRmtw/s9tg=; b=AXrSstwCUqD/G0EgqhehhtT2wrx8JXIUOWb/1wBaRGgkl/NOXXeIwJQrq/BlCOuTiz L3Wv2aIyv2PpfL0KUkMFY8gHSrv65kMMuLsJ/MVvvo7FJupeG7dE6Mn++w6TyMdWfDap NCLzkBjziODMEBQz6L7t0D4QnKzdgbR4vfuuHFq4MUUCEE6sixc/8NejJ8sp5y+M333R tRR6dB2OJ7x8/mKmtsSSzAFB0b8pq+BI9honyFtdsS7gBOehaljJuI2INaCc8+j9zNMh YCM6OAHtj2lvASy2aIw5zj9dGPGM+eNKTkrut2IIqYnLdY4TBjvvA85pq1FWBxD/d/qs Ts7A== X-Gm-Message-State: ALoCoQlXuRTSAWrvkpzwa0lcHjaNX7J6hdzkAnIWGfvTciIn7zQ/uhPkdceoUd92pyn68YO35C75 X-Received: by 10.152.184.73 with SMTP id es9mr18830233lac.4.1431975440730; Mon, 18 May 2015 11:57:20 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.7.135 with SMTP id j7ls505567wia.22.canary; Mon, 18 May 2015 11:57:19 -0700 (PDT) X-Received: by 10.194.84.100 with SMTP id x4mr17451520wjy.69.1431975439531; Mon, 18 May 2015 11:57:19 -0700 (PDT) Original-Received: from smtp.smtpout.orange.fr (smtp05.smtpout.orange.fr. [80.12.242.127]) by mx.google.com with ESMTPS id ck1si19226865wjc.67.2015.05.18.11.57.19 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 18 May 2015 11:57:19 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.127 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.127; Original-Received: from new-host.home ([92.139.141.131]) by mwinf5d61 with ME id VWxJ1q00X2qJ0z803WxJwf; Mon, 18 May 2015 20:57:19 +0200 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Mon, 18 May 2015 20:57:19 +0200 X-ME-IP: 92.139.141.131 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.127 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mail=vicente.botet@wanadoo.fr 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:17944 Archived-At: This is a multi-part message in MIME format. --------------010703090002040307090707 Content-Type: text/plain; charset=UTF-8; format=flowed Hi, In one of the variant threads, BS presented this language like example of pattern matching on sum types (union, variants) int area(variant v) { inspect(v) { // look at the variant v match Circle c: return pi*square(c.radius()); match Square s: return s.height()*s.width(); } } It easy to extend the inspection/matching to multiple sum types. A library solution applied to multiple variants could be inspect(v, b).match( [](Circle c, int j ) { }, [](auto i, autoj ) { // ... } ); This is quite close to the when_all(f1, f2).then(); expressions. This let me think that we could have a match function for futures because a future has either a value or an exception_ptr, so a sum type f.match( [](Circle c) { }, [](auto) { // ... } ); and that when_all would be close to inspect but applied to futures when_all(a, b).match( [](Circle, int j ) { }, [](auto i, auto j ) { // ... } ); Just wanted to share this similarity. Vicente -- --- 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/. --------------010703090002040307090707 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi,

In one of the variant threads, BS presented this language like example of pattern matching on sum types (union, variants)


=C2=A0=C2=A0=C2=A0 int area(variant<Circle,Square> v)
=C2=A0=C2=A0=C2=A0 {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 inspect(v) {=C2=A0=C2=A0=C2= =A0 // look at the variant v
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 match Circle c:=C2=A0=C2=A0= =C2=A0=C2=A0 return pi*square(c.radius());
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 match Square s:=C2=A0=C2=A0 = return s.height()*s.width();
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
=C2=A0=C2=A0=C2=A0 }

It easy to extend the inspection/matching to multiple sum types.

A library solution applied to multiple variants could be

inspect(v, b).match(
  [](Circle c, int j )
    {
    },
  [](auto i, autoj )
    {
      // ...
    }
  );
This is quite close to the when_all(f1, f2).then(); expressions. This let me think that we could have a match function for futures because a future has either a value or an exception_ptr, so a sum type

f.match(
  [](Circle c)
    {
    },
  [](auto)
    {
      // ...
    }
  );

and that when_all would be close to inspect but applied to futures
when_all(a, b).match(
  [](Circle, int j )
    {
    },
  [](auto i, auto j )
    {
      // ...
    }
  );

Just wanted to share this similarity.

Vicente


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