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= Module CharClass =

Programs that deal with characters and strings often need to perform tests that "classify a character." Is the character a letter? A digit? A whitespace character? and so forth.

Module CharClass provides a set of boolean function procedures that are used for such classification of values of the type CHAR. All procedures accept a single argument of type CHAR and return a BOOLEAN result.

Recall that Oberon-2 is defined so that characters are ordered in the same manner as defined by ASCII. Specifically, all the digits precede all the upper-case letters, and all the upper-case letters precede all the lower-case letters. This assumption is carried over into module CharClass. Also, note that CharClass uses constants defined in module Ascii within many of its procedures (see section Module Ascii)

== Example ==

For example, the function IsLetter is used to test whether a particular character is one of `A' through `Z' or `a' through `z':

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Out.String("The character '");
IF CharClass.IsLetter(c) THEN
   Out.Char(c); 
   Out.String("' is a letter."); 
ELSE
   Out.Char(c); 
   Out.String("' isn't a letter."); 
END;
Out.Ln
</syntaxhighlight>


== Note ==
Please note: None of these predicates are affected by the current localization setting. For example, IsUpper will always test for "A"<=ch & ch<="Z" regardless of whether the locale specifies that additional characters belong to this set or not. The same holds for the compare and capitalization procedures in module Strings.

Constant: eol

The implementation-defined character used to represent end-of-line internally by OOC (see section Module Ascii) 

Read-only Variable: systemEol

An implementation defined string that represents the end-of-line marker used by the target system for text files. systemEol may be more than one character in length, and is not necessarily equal to eol. Note that systemEol is a string; it is always terminated by 0X (i.e., systemEol cannot contain the character `0X'). 

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsNumeric (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch is classified as a numeric character (i.e., a decimal digit---`0' through `9'). 

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsLetter (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch is classified as a letter. 

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsUpper (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch is classified as an upper-case letter. 

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsLower (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch is classified as a lower-case letter. 

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsControl (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch represents a control function (that is, an ASCII character that is not a printing character). 

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsWhiteSpace (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch represents a space character or other "format effector". IsWhiteSpace returns TRUE for only these characters:

` ' -- space (i.e., `Ascii.sp')

`Ascii.ff' -- formfeed

`Ascii.cr' -- carriage return

`Ascii.ht' -- horizontal tab

`Ascii.vt' -- vertical tab

<syntaxhighlight lang="oberon2" style="font-size:10pt">
Function: IsEOL (ch: CHAR): BOOLEAN
</syntaxhighlight>
Returns TRUE if, and only if, ch is the implementation-defined character used to represent end of line internally.

==Origin==

{{ModulesPortedFromOOCLibrary}}

{{SourceOptimizingOberonCompilerReferenceManual}}
[[Category:Modules]]