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 January 2004|
|PDF File Size:||1.70 Mb|
|ePub File Size:||3.63 Mb|
|Price:||Free* [*Free Regsitration Required]|
JFlex is not sponsored by jkex affiliated with Sun Microsystems, Inc. Next to package and import statements there is usually not much to do here.
JFlex User’s Manual
If more than one end of file code directive jldx present, the code will be concatenated in order of appearance in the specification. See section 6 performance of this manual to compare these methods. Since Yacc’s architecture is a bit different from CUP’s, the interface setup also works in a slightly different manner.
The default end jlsx file value under this setting is YYEOFwhich is a public static final int member of the generated class. The same StateGroup see section 4. And also the other way around: StringCharacter an escape sequence or any unicode character that is not one of these meta characters: This can be useful in combination with the negation operator!
JFlex User’s Manual
The last lexical rule in the example specification is used as an error fallback. All subsequent calls to the scanning method will return the end of file value void yyreset java.
Therefore lookahead expressions could cause major headaches. Note that this exception is only for internal scanner errors. This feature is still experimental.
The action code will only be executed when the end of file is read and the scanner is currently in one of the lexical states listed in StateList.
All options and the complete specification syntax are presented in Lexical specifications section 4 ; Encodings, Platforms, and Unicode section 5 provides information about scannig text vs.
Manuaal is possible, but not considered as good Java programming style to put manuwl helper class such as token classes in this section. This is not allowed in JFlex and you will have to transform such definitions.
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.
Identifier matches each string that starts with a character of class jletter followed by zero or more characters of class jletterdigit. Prints line, column, matched text, and CUP symbol name for each returned token to standard out.
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. Both options cause the generated scanner to use the full Unicode input character set, including supplementary code points: Of course the encoding to use can also come from the data itself: The corresponding JFlex specification could look somewhat like this: In both cases the look-ahead is not consumed and not included in the matched text region, but it is considered while determining which rule has the longest match see also How the input is matched.
This method is only available in the skeleton file skeleton.
JLex: A Lexical Analyzer Generator for Java(TM)
Although this allows a grammar like specification style, macros are still just abbreviations and not non terminals – they cannot be recursive or mutually recursive. It works, but error reporting can be strange if a syntax error occurs on the last token in the included file.
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 Java does this as follows: See also section 5 for information about character encodings.
Here you can define your own member variables and functions in the generated scanner. It’s easier because you want the raw bytes and not their meaning, i. State declarations State declarations have the following from: They will be read again in the next call of the scanning method.