Re: The extension of Is_Basic to unicode (about AI12-0260-1)

[ytomino <aghia05@gmail.com>]

On Thursday, April 12, 2018 at 7:20:28 AM UTC+9, Randy Brukardt wrote:
> "J-P. Rosen" <rosen@adalog.fr> wrote in message 
> news:palsmv$g18$1@gioia.aioe.org...
> > Le 11/04/2018 à 16:32, Dan'l Miller a écrit :
> >>> True if Item is a basic letter. A basic letter is a character that
> >>> is in one of the ranges 'A'..'Z' and 'a'..'z', or that is one of
> >>> the following: 'Æ', 'æ', 'Ğ', 'ğ', 'Ş', 'ş', or 'ß'.
> >> If this Ada-specific definition of this is-basic/base-Latin-letter
> >> property is the official normative list, then it seems rather
> >> arbitrary and capricious, not conforming to Unicode or to linguistic
> >> reality.
> >>
> >> In Unicode-speak's terminology/jargon, the definition of base
> >> character at https://definedterm.com/a/definition/160575 would admit
> >> quite a few more, [...]
> > The above Is_Basic is about Character, and is defined only when using
> > Latin-1. Unicode is a different standard.
> 
> Moreover, its definition is historical -- it was defined this way for Ada 
> 95, and whether or not that would be the correct definition had it been 
> defined in 2018 is irrelevant. Changing the definition would potentially 
> silently break programs that use it. There are a number of things in 
> Ada.Characters.Handling that aren't correct for Unicode purposes, one of 
> them is even called out by the third note in A.3.2.
> 
>                       Randy.

Thanks for your detailed description.

If Character.Handling.Is_Basic can not be changed because compatibility, still more, this *overloading* will create new problem for the future.

For example, on rewriting some applications from Character to Wide_Character, it may be imagined that two meanings of Is_Basic will confuse.
Or, they makes hard to use "use clause", or use as a generic formal subprogram.

Excuse me for repeating, should new function name be used for new definition?

  function Is_Base (Item : Wide_Character) return Boolean; -- according with Unicode
  function Is_Basic (Item : Wide_Character) return Boolean is (Is_Base (Item) and Is_Letter (Item)); -- for compatibility