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.
|Published (Last):||21 October 2008|
|PDF File Size:||6.53 Mb|
|ePub File Size:||4.59 Mb|
|Price:||Free* [*Free Regsitration Required]|
The following table shows the results that were produced by the scanner specification of a small toy programming language the example from the JLex website. The following scenario works like a breeze: Here you can define your own member variables and functions in the generated scanner. There is no guarantee that the values of these integer constants are distinct.
You can just concentrate on your grammar. Flex offers the ones directly supported by C, JFlex offers the ones supported by Java. When constructing the InputStreamReaderyou can give the encoding as argument.
JLex: A Lexical Analyzer Generator for Java(TM)
jleex The section on porting scanners shows how to port scanners from JLex, and from the lex and flex tools for C. In the optimal case, each character is only examined once, in some situations explained below, a small amount of backtracking is necessary to determine the longest match.
The second part of the lexical specification contains options and directives to customise the generated lexer, declarations of lexical states and macro definitions. In JLex, the right hand side of a macro is just a piece of text that is copied to the point where the macro is used. It builds on many helpful suggestions and comments from Larry Bell.
JFlex jles always manuao second form of expansion, since this is the natural form of thinking about abbreviations for regular expressions. Since CUP version 0. Causes the scanning method to be declared as of the Java wrapper type Integer.
The lexical rules section of a JFlex specification contains regular expressions and actions Java code that are executed when the scanner matches the associated regular expression. The pushed back characters will after the call of yypushback not be included in yylength and yytext.
You can just concentrate on your grammar. JFlex comes with a skeleton file in the src directory that reflects exactly the internal, pre-compiled skeleton and can be used with the -skel option. Use only when you know what you are doing! The preceding line terminator in the input is not consumed and can be matched by another rule.
When in doubt or when requirements are not or not yet fixed: This regular expression may itself contain macro usages. This section concentrates on the CUP side of the story.
This section gives details about JFlex 1. The two main rules of optimization apply also for lexical specifications: If the end of file is reached, the scanner executes the EOF action, and also upon each further call to the scanning method returns the specified EOF value. The example is for site wide installation. You can fix the problem by telling Java explicitly which msnual to use.
JFlex attempts to report such cases at generation time, but it might be overeager: JFlex comes with a directory examplesmnual you can find a small standalone scanner that doesn’t need other tools like CUP to give you a running example.
More information about encodings, which ones are supported, how they are called, and how to set them may be found in the official Java documentation in the chapter about internationalization. It also consumes memory proportional to the size of the matched input for r1 r2. The calling main procedure would then construct the parser as shown ljex the section above. Getting rid of backtracking is messy and often may be an enormous amount of work for a complicated scanner. These escape sequences should be manuql into their octal or hexadecimal equivalent.
JLex: A Lexical Analyzer Generator for Java(TM)
Access to the genarated class is expected to be mediated by user class code see next switch. With input “averylongjoke” the scanner has to read all charcters up to ‘j’ to decide that rule. Causes the scanning method to be declared as returning values of the specified type.
Flex offers the character classes directly supported by C, JFlex offers the ones supported by Java. To meet this requirement, if an implementation provides for case-insensitive matching, then it shall provide at least the simple, default Unicode case-insensitive matching, and specify which properties are closed and which are not.
Java does this as follows: If a program reads a file from disk, what it really reads is a stream of bytes. As shown in the example jelx, this is the place to put package declarations and import statements. What is read and what constitutes a character depends on the runtime platform. Scanning is performed after that translation and both match.
In flex more special characters lose their meaning in character classes. The syntax and semantics of joex expressions manul flex are pretty much the same as in JFlex. The class will have a constructor taking a java. The algorithm JFlex currently uses for matching jllex context expressions manul the one described in [ 1 ] leading to the deficiencies mentioned above.
You may however define a specific value to return and a specific piece of code that should be executed when the end of file is reached.
This section concentrates on the CUP side of the story. It is DFA-based deterministic finite automata and does mlex require backtracking over alternative as for instance perl-style regular expression matching does.
Backtracking can be avoided in general by adding error rules that match those error conditions “av” “ave” “avery” “averyl”.