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Author:halw

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Date:2008-12-10T05:29:55.000000Z


git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@134 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
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halw
2008-12-10 05:29:55 +00:00
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documentation/current/solutions/text-processing/eiffellex/eiffellex-tutorial.wiki
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@@ -227,6 +227,7 @@ The Lex library supports a powerful set of construction mechanisms for describin
Let us now study the format of regular expressions. This format is used in particular for the lexical grammar files needed by class [[ref:/libraries/lex/reference/scanning_chart|SCANNING]] and (as seen below) by procedure <eiffel>read_grammar</eiffel> of class [[ref:/libraries/lex/reference/metalex_chart|METALEX]] . The ''eiffel_regular'' grammar file in the examples directory provides an extensive example.
Each regular expression denotes a set of tokens. For example, the first regular expression seen above, <br/>
<code>
'0'..'9'
</code>
@@ -299,7 +300,7 @@ Concatenations may be inconvenient when the concatenated elements are simply cha
More generally, a string is written "a <code>1</code> a <code>2</code> ... a <code>n</code>" for ''n >= 0'', where the "a <code>i</code>" are characters, and is an abbreviation for the concatenation 'a <code>1</code>' 'a <code>2</code>' ... 'a <code>n</code>', representing a set containing a single token. In a string, the double quote character " is written \" and the backslash character \ is written \\. No other special characters are permitted; if you need special characters, use explicit concatenation. As a special case, "" represents the set containing a single empty token.
A union, writtenexp <code>1</code> | exp <code>2</code> | ... | exp <code>n</code>, describes the set of tokens which are specimens of exp <code>1</code>, or of exp <code>2</code>, etc. For example, the union ''('a'..'z') | ('A'..'Z')'' describes the set of single-letter tokens (lower-case or upper-case).
A union, written exp <code>1</code> | exp <code>2</code> | ... | exp <code>n</code>, describes the set of tokens which are specimens of exp <code>1</code>, or of exp <code>2</code>, etc. For example, the union ''('a'..'z') | ('A'..'Z')'' describes the set of single-letter tokens (lower-case or upper-case).
===Predefined expressions===