JLex directives: This includes macro definitions (described below). See the JLex Reference Manual for more information about this part of the specification. ~appel/modern/java/CUP/ □. A ready-to-use JLex spec. (*.lex). CUP spec. (*.cup). Lexical analyzer. (*.java). Nodes of the. The next section of this manual describes installation procedures for JFlex. If you never worked with JLex or just want to compare a JLex and a.

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If you want to provide your own constructor for the lexer, you should always call the generated one in it to initialize the input buffer. Also, you should take care when you write your lexer spec: In a lexical rule, a regular expression r may be followed by a look-ahead expression. File a file name, either absolute or relative to the directory containing the lexical specification. It costs multiple additional comparisons per input character and the matched text has to be re-scanned for counting.

Here you can define your own member variables and functions in the generated scanner.

Mamual are more subtle kinds of errors that can be introduced by JLex macros. They are pointers into the generated DFA table, and if JFlex recognises two states as lexically equivalent if they are used with the exact same set of regular expressionsthen the two constants will get the same value. This feature is still in alpha status, and not fully implemented yet.

JLex: A Lexical Analyzer Generator for Java(TM)

JFlex is a lexical analyser generator for Java 1 written in Java. Basic structure A lexical specification for flex has the following basic structure: With this, things like. Differently to JLex, macros are not just pieces of text that are expanded by copying – they are parsed and must be well formed.


Prints line, column, matched text, and CUP symbol name for each returned token to standard out. In that way, we get for input ” break ” the keyword ” break ” and not an Identifier ” break “. JFlex can easily be integrated with the Ant build tool. Additional to regular expression matches, one can use lexical states to refine a specification.

Lexical states can be used to jled restrict the set of regular expressions that match the current input. Syntax The syntax of the “lexical rules” section is described by the following BNF grammar terminal symbols are enclosed in ‘quotes’: The same reason as above 64 KB size limitation of methods causes the same problem, when the scanner gets too big. They are used as in the NL token above. This is mainly for JFlex maintenance and special low level customisations.

JFlex User’s Manual

In particular, where UTF is used, a sequence consisting of a leading surrogate followed by a trailing surrogate shall be handled as a single code point in matching. It was however possible to further improve the performance of generated scanners using JFlex.

Creates a main function in the generated class that expects the name of an input file on the command line and then runs mqnual scanner on this input file by printing information about each returned token to the Java console until the end of file is reached.

What is read and what constitutes a character depends on the runtime platform.

JLex: A Lexical Analyzer Generator for Java(TM)

The second part of klex lexical specification contains options and directives to customise the generated lexer, declarations of lexical states and macro definitions. Actions in the specification can then return int values as tokens. You can redefine the name and return type of the method and it is possible to declare exceptions that may be thrown in one of the actions of the specification. To make things work correctly, you still have to know where you are and how to map byte values to Unicode characters and vice versa, but the important thing is, that this mapping is at least possible you can map Kanji characters to Unicode, but you cannot map them to ASCII or iso-latin In the best case, the trailing context will first have to be read and then because it is not to be consumed re-read again.


In most scanners it is possible to do the line counting in the specification by incrementing yyline each time a line terminator manuap been matched.

A regular expression that consists solely of a Character matches this character. As shown in the example spec, this is the place to put package declarations and import statements.

JFlex User’s Manual

JFlex applies the following standard operator precedences in regular expression from highest to lowest:. I’d like to add, that I do not think, that the handwritten scanner from the CUP website used here in the test is stupid or badly written or anything like that. They should get their own. Tells JFlex to give the generated class the name classname and to write the generated code to a file classname. Actions in the specification can then return Integer values as tokens.

These classes will sometimes have to be listed manually if there is need for this feature, it may be implemented in a future JFlex version. It is of course possible to provide a dummy implementation of that method in the class code jled if you still want to override the function name.