[antlr-interest] Can never be matched

[Patrick Higgins]

I don't know what your grammar is supposed to be doing, but from the looks of it, there's a lot of confusion and unfortunately I wouldn't say that you're "almost done".

Are you using ANTLR because your course asks you to specifically use it and you have some examples and explanations of how to use it, or does your course not specify any particular tool and you're just using ANTLR as a tool to understand grammars? I ask this because of your INTEGER rule. The way you have defined it is not optimal for ANTLR and makes me think you grabbed it from a grammar that was not intended for use with ANTLR.

Your token for DIGIT and INTEGER will actually match the same input. Can you take a look at it and explain why?

The general problem I see is that you seem to be confused about what should be lexer rules and what should be parser rules, and ANTLR makes it a little confusing (although convenient) by allowing both in a single file. That bit of confusion is also what makes me suspect you've been looking at some grammars that were not designed for ANTLR.

Do you not have access to a professor, TA, or even a book to gain an understanding of the basics?



----- Original Message ----
From: Bryan S Follins <asalh at mindspring.com>
To: John B. Brodie <jbb at acm.org>
Cc: antlr-interest at antlr.org
Sent: Sunday, July 19, 2009 1:10:11 PM
Subject: [antlr-interest] Can never be matched

I'm almost done with a lesson grammar but I ran into a problem   I get an
error referencing the TOKEN RULE,  which is on Line 17 (TOKEN : ID)  It also
references Line 20, where there is a blank before SEPERATOR.  

The error reads: error (line)20.1: groupassign.g(file name) (line)17:8:  The
following alternatives can never be matched: 2,3

Does anyone know what that error code means?

Code is below:

grammar groupassign;
@header{
import java.util.HashMap;
}
@members{
HashMap memory = new HashMap();
}

prog                       :               WS        
                                |              COMMENT
                                |              TOKEN;
                                
WS                         :               (' '|'\t'|'\n'|'\r\n')+{skip();};
COMMENT                         :               '//'
                                                {~('\n'|'\r'|'\r\n'))*
('\n'|'\r'|'\r\n'('\n')?)
                                                {$setType(Token.SKIP};
newline();};
TOKEN                  :               ID            
                                |              KEYWORD
                                |              LITERAL
                                |              SEPERATOR
                                |              OPERATOR;
ID                            :               (LETTER| DIGIT) (LETTER)*;
LETTER                  :               ('a'..'z'|'A'..'Z')+;
DIGIT                     :               ('0'..'9')+;
KEYWORD                           :
('boolean'|'else'|'if'|'int'|'main'|'void'|'while'|'print');
LITERAL                                :               BOOLEAN 
                                |              INTEGER;
INTEGER              :               DIGIT
                                |              INTEGER DIGIT;
SEPERATOR        :               ('('|')'|'{'|'}'|';'|',');
BOOLEAN            :               ('true'|'false');
OPERATOR          :
('='|'+'|'-'|'*'|'/'|'<'|'<='|'>'|'>='|'=='|'!='|'&&'|'||'|'!');
                                

                                


                                
                                




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