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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Semantic values are expected in a field yylval of type parserval where parser is the name of the generated parser class. Symbol objects with position information of the current token see section 8.
Lexical states are declared and used as Java int constants in the generated class under the same name as they are used in the specification.
JFlex User’s Manual
It eliminates some very hard to find bugs in lexical specifications such like not having parentheses around more complicated macros – which is not necessary with JFlex. Working with JFlex – an example runs through an example specification and explains how it works. Flex offers the character classes directly supported by C, JFlex offers the ones supported by Java. The end of file There is always a default value that the scanning method will return when the end of file has been reached.
The next section of this manual describes installation procedures for JFlex. A lexical state acts like a start condition. Class options and user class jle These options regard name, constructor, API, and related parts of the generated scanner class. The minimal set of properties is supported, as well as a few others. Most times it is. Reader object which is passed to the lexer in the generated constructor.
In the JFlex source the directive. The string break in a specification is for instance handled like the expression [bB][rR][eE][aA][kK]. It costs multiple additional comparisons per input character and the matched text has to be re-scanned for counting. State identifiers are letters followed by a sequence of letters, digits or underscores.
There will be no runtime overflow when using this set of input characters. Note that writing more rules in a specification does not make the generated scanner slower except when you have to switch to another code generation method because of the larger size.
When consuming its input, the scanner determines the regular expression that matches the longest portion of the input longest match rule. The int member variable yycolumn contains the number of characters starting with 0 from the beginning of the current line to the beginning of the current token. For arbitrary lookahead also called trailing context the expression is matched only when followed by input that matches the trailing context.
It sounds quite easy, and actually it is no big deal, but ljex are a few little pitfalls on the way. This assumes that the generated parser will get the name parser. They are used as in the NL token above.
JFlex User’s Manual
Check lookahead expressions manually. It is of manuwl possible to provide a dummy implementation of that method in the class code section if you still mabual to override the function name. They were tested on different. Its internal implementation may change between releases or skeleton files without notice. The problem for binaries is that JFlex scanners are designed to work on text. They will be ignored by JFlex. JFlex was designed to read old JLex specifications unchanged and to generate a scanner which behaves exactly the same as the one generated by JLex with the only difference of being faster.
The main difference from older CUP versions to 0. 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. JFlex generates exactly one file containing one class from the specification unless you have declared another class in the first specification section.
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. The calling main procedure would then construct the parser as shown in the section above. Those are roughly in order of performance gain:.
In addition to regular expression matches, one can use lexical states to refine a specification. Therefore it should also be the most convenient one.
There are no special parser codeinit code or scan with options any more that you have to provide in your CUP parser specification. The syntax and semantics of regular expressions in flex are pretty much the same as in JFlex.
Rules and Actions 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. An Action consists either of a piece of Jldx code enclosed in curly braces or is the special action.