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A.3.2 The Package Characters.Handling

Static Semantics

1
The library package Characters.Handling has the following declaration: 
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{AI95-00362-01} {AI95-00395-01} with Ada.Characters.Conversions;
package Ada.Characters.Handling is
  pragma Pure(Handling);
3
--Character classification functions
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{AI05-0185-1}   function Is_Control           (Item : in Character) return Boolean;
  function Is_Graphic           (Item : in Character) return Boolean;
  function Is_Letter            (Item : in Character) return Boolean;
  function Is_Lower             (Item : in Character) return Boolean;
  function Is_Upper             (Item : in Character) return Boolean;
  function Is_Basic             (Item : in Character) return Boolean;
  function Is_Digit             (Item : in Character) return Boolean;
  function Is_Decimal_Digit     (Item : in Character) return Boolean
                     renames Is_Digit;
  function Is_Hexadecimal_Digit (Item : in Character) return Boolean;
  function Is_Alphanumeric      (Item : in Character) return Boolean;
  function Is_Special           (Item : in Character) return Boolean;
  function Is_Line_Terminator   (Item : in Character) return Boolean;
  function Is_Mark              (Item : in Character) return Boolean;
  function Is_Other_Format      (Item : in Character) return Boolean;
  function Is_Punctuation_Connector (Item : in Character) return Boolean;
  function Is_Space             (Item : in Character) return Boolean;
5
--Conversion functions for Character and String
6
  function To_Lower (Item : in Character) return Character;
  function To_Upper (Item : in Character) return Character;
  function To_Basic (Item : in Character) return Character;
7
  function To_Lower (Item : in String) return String;
  function To_Upper (Item : in String) return String;
  function To_Basic (Item : in String) return String;
8
--Classifications of and conversions between Character and ISO 646
9
  subtype ISO_646 is
    Character range Character'Val(0) .. Character'Val(127);
10
  function Is_ISO_646 (Item : in Character) return Boolean;
  function Is_ISO_646 (Item : in String)    return Boolean;
11
  function To_ISO_646 (Item       : in Character;
                       Substitute : in ISO_646 := ' ')
    return ISO_646;
12
  function To_ISO_646 (Item       : in String;
                       Substitute : in ISO_646 := ' ')
    return String;
13/2
{AI95-00285-01} {AI95-00395-01} -- The functions Is_Character, Is_String, To_Character, To_String, To_Wide_Character,
-- and To_Wide_String are obsolescent; see J.14.
Paragraphs 14 through 18 were deleted.
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{AI95-00395-01}
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{AI95-00395-01}
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{AI95-00395-01}
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{AI95-00395-01}
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{AI95-00395-01}
19
end Ada.Characters.Handling;
19.a/2
Discussion: {AI95-00395-01} The with_clause for Ada.Characters.Conversions is needed for the definition of the obsolescent functions (see J.14). It would be odd to put this clause into J.14 as it was not present in Ada 95, and with_clauses are semantically neutral to clients anyway. 
20
In the description below for each function that returns a Boolean result, the effect is described in terms of the conditions under which the value True is returned. If these conditions are not met, then the function returns False.
21
Each of the following classification functions has a formal Character parameter, Item, and returns a Boolean result. 
22
Is_Control 
True if Item is a control character. A control character is a character whose position is in one of the ranges 0..31 or 127..159.
23
Is_Graphic 
True if Item is a graphic character. A graphic character is a character whose position is in one of the ranges 32..126 or 160..255.
24
Is_Letter 
True if Item is a letter. A letter is a character that is in one of the ranges 'A'..'Z' or 'a'..'z', or whose position is in one of the ranges 192..214, 216..246, or 248..255.
25
Is_Lower 
True if Item is a lower-case letter. A lower-case letter is a character that is in the range 'a'..'z', or whose position is in one of the ranges 223..246 or 248..255.
26
Is_Upper
True if Item is an upper-case letter. An upper-case letter is a character that is in the range 'A'..'Z' or whose position is in one of the ranges 192..214 or 216.. 222.
27
Is_Basic 
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', 'Ð', 'ð', 'Þ', 'þ', or 'ß'.
28
Is_Digit 
True if Item is a decimal digit. A decimal digit is a character in the range '0'..'9'.
29
Is_Decimal_Digit 

A renaming of Is_Digit.
30
Is_Hexadecimal_Digit

True if Item is a hexadecimal digit. A hexadecimal digit is a character that is either a decimal digit or that is in one of the ranges 'A' .. 'F' or 'a' .. 'f'.
31
Is_Alphanumeric 

True if Item is an alphanumeric character. An alphanumeric character is a character that is either a letter or a decimal digit.
32
Is_Special 
True if Item is a special graphic character. A special graphic character is a graphic character that is not alphanumeric.
32.1/3
   {AI05-0185-1} Is_Line_Terminator

True if Item is a character with position 10 .. 13 (Line_Feed, Line_Tabulation, Form_Feed, Carriage_Return) or 133 (Next_Line).
32.2/3
   {AI05-0185-1} Is_Mark

Never True (no value of type Character has categories Mark, Non-Spacing or Mark, Spacing Combining).
32.3/3
   {AI05-0185-1} Is_Other_Format

True if Item is a character with position 173 (Soft_Hyphen).
32.4/3
   {AI05-0185-1} Is_Punctuation_Connector

True if Item is a character with position 95 ('_', known as Low_Line or Underscore).
32.5/3
   {AI05-0185-1} Is_Space

True if Item is a character with position 32 (' ') or 160 (No_Break_Space).
33
Each of the names To_Lower, To_Upper, and To_Basic refers to two functions: one that converts from Character to Character, and the other that converts from String to String. The result of each Character-to-Character function is described below, in terms of the conversion applied to Item, its formal Character parameter. The result of each String-to-String conversion is obtained by applying to each element of the function's String parameter the corresponding Character-to-Character conversion; the result is the null String if the value of the formal parameter is the null String. The lower bound of the result String is 1. 
34
To_Lower
Returns the corresponding lower-case value for Item if Is_Upper(Item), and returns Item otherwise.
35
To_Upper
Returns the corresponding upper-case value for Item if Is_Lower(Item) and Item has an upper-case form, and returns Item otherwise. The lower case letters 'ß' and 'ÿ' do not have upper case forms.
36
To_Basic
Returns the letter corresponding to Item but with no diacritical mark, if Item is a letter but not a basic letter; returns Item otherwise. 
37
The following set of functions test for membership in the ISO 646 character range, or convert between ISO 646 and Character.
38
Is_ISO_646
The function whose formal parameter, Item, is of type Character returns True if Item is in the subtype ISO_646.
39
Is_ISO_646
The function whose formal parameter, Item, is of type String returns True if Is_ISO_646(Item(I)) is True for each I in Item'Range.
40
To_ISO_646
The function whose first formal parameter, Item, is of type Character returns Item if Is_ISO_646(Item), and returns the Substitute ISO_646 character otherwise.
41
To_ISO_646
The function whose first formal parameter, Item, is of type String returns the String whose Range is 1..Item'Length and each of whose elements is given by To_ISO_646 of the corresponding element in Item. 
Paragraphs 42 through 49 were deleted. 
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 {AI95-00285-01} {AI95-00395-01}
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 {AI95-00285-01} {AI95-00395-01}
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 {AI95-00285-01} {AI95-00395-01}
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 {AI95-00285-01} {AI95-00395-01}
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 {AI95-00285-01} {AI95-00395-01}
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 {AI95-00285-01} {AI95-00395-01}

Implementation Advice

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 {AI95-00285-01}
NOTES
50
5  A basic letter is a letter without a diacritical mark.
51
6  Except for the hexadecimal digits, basic letters, and ISO_646 characters, the categories identified in the classification functions form a strict hierarchy:
52
— Control characters
53
— Graphic characters
54
    — Alphanumeric characters
55
        — Letters
56
            — Upper-case letters
57
            — Lower-case letters
58
        — Decimal digits
59
    — Special graphic characters
59.a
Ramification: Thus each Character value is either a control character or a graphic character but not both; each graphic character is either an alphanumeric or special graphic but not both; each alphanumeric is either a letter or decimal digit but not both; each letter is either upper case or lower case but not both.
60/3
7  {AI05-0114-1} There are certain characters which are defined to be lower case letters by ISO 10646 and are therefore allowed in identifiers, but are not considered lower case letters by Ada.Characters.Handling.
60.a/3
Reason: This is to maintain runtime compatibility with the Ada 95 definitions of these functions. We don't list the exact characters involved because they're likely to change in future character set standards; the list for ISO 10646:2011 can be found in AI05-0114-1.
60.b/3
Ramification: No version of Characters.Handling is intended to do portable (Ada-version independent) manipulation of Ada identifiers. The classification given by Wide_Characters.Handling will be correct for the current implementation for Ada 2012 identifiers, but it might not be correct for a different implementation or version of Ada. 

Extensions to Ada 95

60.c/2
{AI95-00362-01} Characters.Handling is now Pure, so it can be used in pure units. 

Incompatibilities With Ada 2005

60.d/3
{AI05-0185-1} Added additional classification routines so that Characters.Handling has all of the routines available in Wide_Characters.Handling. If Characters.Handling is referenced in a use_clause, and an entity E with a defining_identifier that is the same as one of the new functions is defined in a package that is also referenced in a use_clause, the entity E may no longer be use-visible, resulting in errors. This should be rare and is easily fixed if it does occur. 

Wording Changes from Ada 95

60.e/2
{AI95-00285-01} {AI95-00395-01} The conversion functions are made obsolescent; a more complete set is available in Characters.Conversions — see A.3.4.
60.f/3
{AI95-00285-01} {AI05-0248-1} We no longer talk about localized character sets; these are a nonstandard mode, which is none of our business. 

Wording Changes from Ada 2005

60.g/3
{AI05-0114-1} Correction: Added a note to clarify that these functions don't have any relationship to the characters allowed in identifiers. 

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