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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: How to convert a string containing two hex digits to a character?
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Date: Sat, 9 Jan 2010 12:33:32 +0100
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Date: 2010-01-09T12:33:28+01:00
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On Sat, 9 Jan 2010 03:13:38 -0800 (PST), Hibou57 (Yannick Duch�ne) wrote:

> I'm welcome to close my comments with more wordings, the addition and
> substraction have a formal logic definition which is based on the
> notion of successor and predecessor, so the most pure and native way
> of doing "+1" and "-1" is to use the successor and predecessor
> function. Ada knows that, yeah ;p (as its 'Pred and 'Succ are more
> universal than its standard "+ and "-" operators)

No. Addition is an operation (in an Abelian group) that may exist
independently on the order relation. As an example consider the complex
numbers, which is a field. As such it has addition and subtraction.
Nevertheless it lacks order, and thus there is no Complex'Pred or
Complex'Succ. And conversely, there can be an order, but no addition.
Example: String.

The guide line should be the semantics. If it is an iteration intended,
then T'Succ is a clear favorite, just because x + 1 has nothing to do with
enumeration. Unfortunately T'Succ is much too verbose, because it
unnecessarily refers to the type.

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