From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Generators/coroutines in future Ada?
Date: Wed, 12 Jul 2017 09:34:02 +0200
Organization: Aioe.org NNTP Server
Message-ID: <ok4jda$1dud$1@gioia.aioe.org>
References: <oju353$b75$1@gioia.aioe.org> <ok001a$rhm$1@gioia.aioe.org>
 <ok26bp$lt4$1@dont-email.me> <ok2hnb$p8q$2@gioia.aioe.org>
 <ok2i7v$pvj$1@gioia.aioe.org> <ok2jfj$t2$1@dont-email.me>
 <ok35rg$1orv$1@gioia.aioe.org> <ok38bc$bo1$1@dont-email.me>
 <ok3c7e$2bd$1@gioia.aioe.org> <ok4fne$j41$1@dont-email.me>
NNTP-Posting-Host: vZYCW951TbFitc4GdEwQJg.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.1
Content-Language: en-US
X-Notice: Filtered by postfilter v. 0.8.2
Xref: news.eternal-september.org comp.lang.ada:47375
Date: 2017-07-12T09:34:02+02:00
List-Id: <comp.lang.ada>

On 12/07/2017 08:35, G.B. wrote:
> On 11.07.17 22:25, Dmitry A. Kazakov wrote:
>> On 2017-07-11 21:22, J-P. Rosen wrote:
>>> Le 11/07/2017 à 20:36, Victor Porton a écrit :
>>>> This state also includes the point of execution (like "We are in the 
>>>> second
>>>> loop in its second operator.")
>>>>
>>>>> This can easily be achieved with a function within a package, where 
>>>>> the
>>>>> package serves to protect and hide the function's state.
>>>> Ada currently has no support to save such (point of execution) states.
>>> It has. Make your generator a task, and have an accept when the data is
>>> ready, which can be nested as deep as you want in any construct.
>>>
>>> A task is a perfect abstraction for a thread of control that maintains
>>> its own execution state!
>>
>> Except that no control is required.
>>
>> I don't understand what is wrong with:
>>
>>    type Stateful is limited private;
>>    function Generate (X : not null access Stateful) return Things;
> 
> Arguably, first, a "function" lacks query/command separation:
> 
>     type Stateful is limited interface;
>     function Current (x : Stateful) return Thing;  -- (*)
>     procedure Next (x : in out Stateful);

I don't understand this example. Why Next cannot be a part of Current? 
Example:

    X := Stack.Pop;

> Not surprisingly, I think, Icon's generators are available to
> use in while-loops that look perfectly ordinary. If Ada requires
> generators to be more explicit:
> 
>     G     : Stateful := Strings.Find
>                (Subject => "...",
>                Pattern => "___");
> 
>     while X of G with condition (X) loop    -- not Ada
>        ...
>     end loop;
> 
> "while ... of ... with" then requires G to be a Stateful.
> Presence of special syntax is, as previously, HOL.

I don't understand this example. If you mean multiple return values 
(tuples), yes Ada should have them, but that is unrelated to stefulness.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de