A.3.2 The Package Characters.Handling
Static Semantics
The library package
Characters.Handling has the following declaration:
--Character classification functions
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;
--Conversion functions for Character and String
function To_Lower (Item :
in Character)
return Character;
function To_Upper (Item :
in Character)
return Character;
function To_Basic (Item :
in Character)
return Character;
function To_Lower (Item :
in String)
return String;
function To_Upper (Item :
in String)
return String;
function To_Basic (Item :
in String)
return String;
--Classifications of and conversions between Character and ISO 646
subtype ISO_646
is
Character
range Character'Val(0) .. Character'Val(127);
function Is_ISO_646 (Item :
in Character)
return Boolean;
function Is_ISO_646 (Item :
in String)
return Boolean;
function To_ISO_646 (Item :
in Character;
Substitute :
in ISO_646 := ' ')
return ISO_646;
function To_ISO_646 (Item :
in String;
Substitute :
in ISO_646 := ' ')
return String;
{
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.
end Ada.Characters.Handling;
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.
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.
Each of the following classification functions has
a formal Character parameter, Item, and returns a Boolean result.
{control
character (a category of Character)} 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.
{graphic
character (a category of Character)} 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.
{letter
(a category of Character)} 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.
{lower-case
letter (a category of Character)} 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.
{upper-case
letter (a category of Character)} 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.
{basic
letter (a category of Character)} 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'.
{decimal
digit (a category of Character)} Is_Digit
True if Item is a decimal digit. A decimal digit is a character
in the range '0'..'9'.
Is_Decimal_Digit
A renaming of Is_Digit.
{hexadecimal
digit (a category of Character)} 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'.
{alphanumeric
character (a category of Character)} Is_Alphanumeric
True if Item is an alphanumeric character. An alphanumeric character
is a character that is either a letter or a decimal digit.
{special
graphic character (a category of Character)} Is_Special
True if Item is a special graphic character. A special graphic character
is a graphic character that is not alphanumeric.
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.
To_Lower
Returns the corresponding lower-case value for Item if Is_Upper(Item),
and returns Item otherwise.
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.
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.
The following set of functions test for membership
in the ISO 646 character range, or convert between ISO 646 and Character.
Is_ISO_646
The function whose formal parameter, Item, is of type Character returns
True if Item is in the subtype ISO_646.
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.
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.
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 48 were deleted.
Implementation Advice
5 A basic letter is a letter without a
diacritical mark.
6 Except
for the hexadecimal digits, basic letters, and ISO_646 characters, the
categories identified in the classification functions form a strict hierarchy:
— Control characters
— Graphic characters
— Alphanumeric characters
— Letters
— Upper-case letters
— Lower-case letters
— Decimal digits
— Special graphic characters
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.
Extensions to Ada 95
{
AI95-00362-01}
{
extensions to Ada 95}
Characters.Handling
is now Pure, so it can be used in pure units.
Wording Changes from Ada 95
{
AI95-00285-01}
We no longer talk about localized character sets; these are a non-standard
mode, which is none of our business.
Sponsored by Ada-Europe