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Date: Mon, 14 May 2012 17:50:07 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: What would you like in Ada202X?
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Date: 2012-05-14T17:50:08+02:00
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On 14.05.12 15:40, Dmitry A. Kazakov wrote:
> On Mon, 14 May 2012 15:09:54 +0200, Georg Bauhaus wrote:
> 
>> On 14.05.12 14:19, Dmitry A. Kazakov wrote:
> 
>>> P.S. I wonder why people keep on calling that thing loop. It has little to
>>> do with iterations. It is a set of paramerized sequences of statements
>>> executed asynchronously with a synchronization point at the end. The syntax
>>> should reflect that.
>>
>> For a start,
>>
>>   for all I in 1 .. 10 do
>>     { stmt }
>>   end do all;
> 
> Yes, I also thought about that, but it still looks much like a loop.

   with all I in 1 .. 10 do
      { stmt }
   end do all;

That's a non-loop indicator up front.

>>   for some I in 1 .. 10 do
>>     { stmt }
>>   end do some;

   with some I in 1 .. 10 do
      { stmt }
   end do some;

> I considered how to do this:
> 
>    up-to-10-instances of
>       ...
>       accept Service_Request do
>           ...
>       end do;
>       ...
>    end;
> 
> The semantics is: accept 1 to 10 calls to the entry Service_Request and
> service all rendezvous concurrently.

How would this work? Expanded into a family? I had thought that each
acceptor servicing would have to perform one atomic sequence, unless
all calls get serviced in the exact same way.

>> While we are at it, can we have goal directed evaluation � la Icon?
>>
>>    while some I ... => P(I, ...) do
>>       { stmt }
>>    end do some;
> 
> The semantics is unclear, how does I change? Is it inference?

The idea is that "some I ..." produces a value as long
as (a) a value is needed and (b) P(I, ...) is true.
This is probably a little vague, and in part syntactic sugar.


procedure Iconic is

   -- <quote>
   -- every subject ? write (find ("fish"));
   -- prints 3, 13, and 23.
   -- </>

   Subject : constant String :=
     "a fish is a fish is a fish";

   Max : constant Natural := 2;
   -- no more than `Max` fish

   function Find
     ( Source : String;
       Pattern : String )
     return Forward_Iterator;

begin
   if some Position in Find(Subject, "fish") => True then
      Put_Line (Natural'Image (Position));
   end if;

   if some Position in Find(Subject, "fish")
     => Position < Subject'Length / 2
   then
      Put_Line (Natural'Image (Position));
   end if;

   while some Position in Find (Subject, "fish")
     => Position < Subject'Length / 2
   do
      Put_Line (Natural'Image (Position));
   end do;

   N := 0;
   while some Position in Find (Subject, "fish")
     => N < Max
   do
      N := N + 1;
      Put_Line (Natural'Image (Position));
   end do;

end Iconic;