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From: "G.B." <bauhaus@notmyhomepage.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Community Input for the Maintenance and Revision of the Ada
 Programming Language
Date: Wed, 4 Oct 2017 23:45:37 +0200
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Xref: news.eternal-september.org comp.lang.ada:48355
Date: 2017-10-04T23:45:37+02:00
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On 04.10.17 21:21, reinert wrote:
> On Tuesday, October 3, 2017 at 8:36:22 AM UTC+2, G.B. wrote:
>> On 03.10.17 05:30, reinert wrote:
>>> I noticed that my compiler did not like for example:
>>>
>>>     t1 : time := clock + 10.0;
>>>     t2 : time := t1 + 20.0;
>>>     t3 : time range t1 + 10.0 .. t2 + 30.0;
>>>
>>>
>>> No room for syntactic sugar here? :-)
>>
>> For a start, the compiler has no idea what "20.0" should
>> mean with regard to Time.
>>
> 
> My compiler (gnat on debian) says "clock + 20" means 20 seconds
> into the future :-)  Assuming I have not misunderstood.

That was confused. What I meant was that
    20.0 Time
has no meaning, since time (moment) is not itself countable,
but duration or span are.

Ada ranges would also be used in for loops that make the program
step through the set of values of the range:

    for Moment in Candy_Time range t1 .. t2 loop
       null;  --  How many iterations will there be?
    end loop;

No such problem when using countable units of time:

    procedure Candy is
       T1 : Day_Number := Day (Clock);
       T2 : Day_Number := T1 + 10;
    begin
       for Day in Day_Number range t1 .. t1 loop
          null;  -- 10 + 1 iterations!
       end loop;
    end Candy;

Thus, by use of proper types the program becomes predictable
at the source level.