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Date: Mon, 11 Jun 2012 19:14:45 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: Practicalities of Ada for app development
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Date: 2012-06-11T19:14:45+02:00
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On 11.06.12 16:43, Dmitry A. Kazakov wrote:
> On Mon, 11 Jun 2012 16:27:30 +0200, Georg Bauhaus wrote:
> 
>> On 11.06.12 10:22, Dmitry A. Kazakov wrote:
>>> On Sun, 10 Jun 2012 23:36:46 +0200 (CEST), Nomen Nescio wrote:
>>>
>>>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote:
>>>>>
>>>>>> Please, why have you defined Code_Point as a modular type?
>>>>>
>>>>> Because code point is unsigned. When you declare something signed
>>>>> you do that because you want negative inverses. Signed integers have
>>>>> the base type with 0 in the middle of its range.
>>>>
>>>> That's no reason to use mod.  You can put boundaries where you want
>>>> them, integer, or mod.
>>>>
>>>> It's about the operators.
>>>
>>> Exactly, there is *no* arithmetic of code points.
>>
>> In case there is no arithmetic of code points, it is really
>> surprising to see
>>
>>    type Code_Point is mod 2**32;
>>
>> and not
>>
>>    type Code_Point is private;
> 
> Code points are numeric:

Numeric to what extent? I'd have thought that code points need little more
than equality and ordering, with conversion functions to/from a "more"
numeric type such as mod 2**32 or a range type.  Either for construction
of code point values, or in case an algorithm wants to use offsets,
or use a table indexed by a numeric subtype made from a "subsection" of
the repertoire.

The construction function could be nicely Unicode-ish when named U:

   PI : constant Code_Point := U+16#03C0#;

> http://en.wikipedia.org/wiki/Unicode


package Unicode_Stuff is

   Data_Error : exception;

   type Unsigned is mod 2**32;

   type Code_Point is private;

   Max_Code_Point : constant := 16#10FFFF#;

   type Non_Code_Point(<>) is limited private;

   U : constant Non_Code_Point;

   function "+"
     (U      : in Non_Code_Point;
      Number : in Unsigned)
   return Code_Point;
   --  raises Data_Error if Number > Max_Code_Point;

private
   type Code_Point is new Unsigned range 0 .. Max_Code_Point;
   type Non_Code_Point is limited null record;
   U : constant Non_Code_Point := (null record);
end Unicode_Stuff;