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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: A few questions
Date: Wed, 4 Nov 2015 19:20:42 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:28218
Date: 2015-11-04T19:20:42-06:00
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"Simon Wright" <simon@pushface.org> wrote in message 
news:lybnb9lote.fsf@pushface.org...
> Simon Wright <simon@pushface.org> writes:
>
>> "Randy Brukardt" <randy@rrsoftware.com> writes:
>>
>>> "Simon Wright" <simon@pushface.org> wrote in message
>>> news:ly611kmh1g.fsf@pushface.org...
>>> ...
>>>> I wrote the attached, using generalized iteration, which bears a
>>>> strong resemblance to the standard container iteration (the names
>>>> bear too strong a resemblance! but this way you can see the
>>>> commonality).
>>>
>>> I suspect you could have written this in a lot simpler
>>> fashion. Something similar to the Prime_Numbers iterator found in the
>>> ACATS foundation (F552A00, look in the support subdirectory,
>>> specifically
>>> http://www.ada-auth.org/cgi-bin/cvsweb.cgi/acats/support/f552a00.a)
>>> would be a starting point. (Thanks again to Brad Moore for creating
>>> this foundation and the associated ACATS tests to give all Ada
>>> implementers something to use as a correct example of iterators.)
>>
>> Great pointer. Though I think the Date case would be a bit more
>> complicated, because you couldn't constrain a Date_Set by Times or
>> Durations.
>
> And I was hoping to write
>
>   with Ada.Text_IO;
>   with F552A00_Prime_Numbers;
>   procedure Primes is
>   begin
>      for P of F552A00_Prime_Numbers.Prime_Number_Set'(Max_Value => 31) 
> loop
>         Ada.Text_IO.Put_Line (P'Img);
>      end loop;
>   end Primes;
>
> but (surprise)
>
>   primes.adb:5:08: cannot iterate over "Prime_Number_Set"

Prime_Number_Set is (directly) an iterator, so you use "in" to iterate over 
it:

 for P in F552A00_Prime_Numbers.Prime_Number_Set'(Max_Value => 31) loop

The "of" form is for iterating over an array or a container whose type has 
the Default_Iterator aspect (which gives the iterator to use).

I can hear the head slap from here. ;-)

                                    Randy.