Just started with JavaCC. But I have a strange behaviour with it. I want to verify input int the form of tokens (letters and numbers) wich are concatenated with signs (+, -, /) and wich can contain parenthesis.
I hope that was understandable 🙂
In the main method is a string, which should produce an error, because it has one opening but two closing parenthesis, but I do not get a parse exception –> Why?
Does anybody have a clue why I don’t get the exception?
I was struggling with left recursion and choice conflicts with my initial try, but managed to get over them. Maybe there I introduced the problem?!
Oh – and maybe my solution is not very good – ignore this fact… or better, give some advice 😉
File: CodeParser.jj
options {
STATIC=false;
}
PARSER_BEGIN(CodeParser)
package com.testing;
import java.io.StringReader;
import java.io.Reader;
public class CodeParser {
public CodeParser(String s)
{
this((Reader)(new StringReader(s)));
}
public static void main(String args[])
{
try
{
/** String has one open, but two closing parenthesis --> should produce parse error */
String s = "A+BC+-(2XXL+A/-B))";
CodeParser parser = new CodeParser(s);
parser.expression();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
PARSER_END(CodeParser)
TOKEN:
{
<code : ("-")?(["A"-"Z", "0"-"9"])+ >
| <op : ("+"|"/") >
| <not : ("-") >
| <lparenthesis : ("(") >
| <rparenthesis : (")") >
}
void expression() :
{
}
{
negated_expression() | parenthesis_expression() | LOOKAHEAD(2) operator_expression() | <code>
}
void negated_expression() :
{
}
{
<not>parenthesis_expression()
}
void parenthesis_expression() :
{
}
{
<lparenthesis>expression()<rparenthesis>
}
void operator_expression() :
{
}
{
<code><op>expression()
}
Edit – 11/16/2009
Now I gave ANTLR a try.
I changed some terms to better match my problem domain. I came up with the following code (using the answers on this site), which seems to do the work now:
grammar Code;
CODE : ('A'..'Z'|'0'..'9')+;
OP : '+'|'/';
start : terms EOF;
terms : term (OP term)*;
term : '-'? CODE
| '-'? '(' terms ')';
And by the way… ANTLRWORKS is a great tool for debugging/visualizing! Helped me a lot.
Additional info
Above code matches stuff like:
(-Z19+-Z07+((FV+((M005+(M272/M276))/((M278/M273/M642)+-M005)))/(FW+(M005+(M273/M278/M642)))))+(-Z19+-Z07+((FV+((M005+(M272/M276))/((M278/M273/M642/M651)+-M005)))/(FW+(M0))))
What kgregory says is the right answer. You can see this if you build the grammar with the DEBUG_PARSER option and then run it:
$ javacc -debug_parser -output_directory=com/testing/ CodeParser.jj && javac com/testing/*.java && java -cp . com.testing.CodeParser Java Compiler Compiler Version 5.0 (Parser Generator) (type "javacc" with no arguments for help) Reading from file CodeParser.jj . . . File "TokenMgrError.java" is being rebuilt. File "ParseException.java" is being rebuilt. File "Token.java" is being rebuilt. File "SimpleCharStream.java" is being rebuilt. Parser generated successfully. Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 1> Consumed token: <<op>: "+" at line 1 column 2> Call: expression Call: operator_expression Consumed token: <<code>: "BC" at line 1 column 3> Consumed token: <<op>: "+" at line 1 column 5> Call: expression Call: negated_expression Consumed token: <"-" at line 1 column 6> Call: parenthesis_expression Consumed token: <"(" at line 1 column 7> Call: expression Call: operator_expression Consumed token: <<code>: "2XXL" at line 1 column 8> Consumed token: <<op>: "+" at line 1 column 12> Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 13> Consumed token: <<op>: "/" at line 1 column 14> Call: expression Consumed token: <<code>: "-B" at line 1 column 15> Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression Consumed token: <")" at line 1 column 17> Return: parenthesis_expression Return: negated_expression Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expressionSee that? The last token consumed is the second to last character – the second to last right parenthesis.
If you want the exception, again, like kgregory said, you could add a new top-level production called “file” or “data” or something and end it with an token. That way any dangling parens like this would cause an error. Here’s an grammar that does that:
options { STATIC=false; } PARSER_BEGIN(CodeParser) package com.testing; import java.io.StringReader; import java.io.Reader; public class CodeParser { public CodeParser(String s) { this((Reader)(new StringReader(s))); } public static void main(String args[]) { try { /** String has one open, but two closing parenthesis --> should produce parse error */ String s = "A+BC+-(2XXL+A/-B))"; CodeParser parser = new CodeParser(s); parser.file(); } catch(Exception e) { e.printStackTrace(); } } } PARSER_END(CodeParser) TOKEN: { <code : ("-")?(["A"-"Z", "0"-"9"])+ > | <op : ("+"|"/") > | <not : ("-") > | <lparenthesis : ("(") > | <rparenthesis : (")") > } void file() : {} { expression() <EOF> } void expression() : { } { negated_expression() | parenthesis_expression() | LOOKAHEAD(2) operator_expression() | <code> } void negated_expression() : { } { <not>parenthesis_expression() } void parenthesis_expression() : { } { <lparenthesis>expression()<rparenthesis> } void operator_expression() : { } { <code><op>expression() }And a sample run:
$ javacc -debug_parser -output_directory=com/testing/ CodeParser.jj && javac com/testing/*.java && java -cp . com.testing.CodeParser Java Compiler Compiler Version 5.0 (Parser Generator) (type "javacc" with no arguments for help) Reading from file CodeParser.jj . . . File "TokenMgrError.java" is being rebuilt. File "ParseException.java" is being rebuilt. File "Token.java" is being rebuilt. File "SimpleCharStream.java" is being rebuilt. Parser generated successfully. Call: file Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 1> Consumed token: <<op>: "+" at line 1 column 2> Call: expression Call: operator_expression Consumed token: <<code>: "BC" at line 1 column 3> Consumed token: <<op>: "+" at line 1 column 5> Call: expression Call: negated_expression Consumed token: <"-" at line 1 column 6> Call: parenthesis_expression Consumed token: <"(" at line 1 column 7> Call: expression Call: operator_expression Consumed token: <<code>: "2XXL" at line 1 column 8> Consumed token: <<op>: "+" at line 1 column 12> Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 13> Consumed token: <<op>: "/" at line 1 column 14> Call: expression Consumed token: <<code>: "-B" at line 1 column 15> Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression Consumed token: <")" at line 1 column 17> Return: parenthesis_expression Return: negated_expression Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression Return: file com.testing.ParseException: Encountered " ")" ") "" at line 1, column 18. Was expecting: <EOF> at com.testing.CodeParser.generateParseException(CodeParser.java:354) at com.testing.CodeParser.jj_consume_token(CodeParser.java:238) at com.testing.CodeParser.file(CodeParser.java:34) at com.testing.CodeParser.main(CodeParser.java:22)Voila! An exception.