Antlr Left-Factoring Grammar

Question

I am new to Antlr. I am defining a grammar for my company using Antlr 3.

Below is my grammar:

grammar Grammar;

@header {
package com.grammar;
}

true        : 'true';
false       : 'false';
null        : 'null';
value       : true | false | null | STRING | NUMBER;
query           : (STATEMENT+) | STATEMENT?;
INSERT      : 'INSERT INTO' TABLE 'VALUES' '('ELEMENTS')'';';
STATEMENT   : INSERT;
STRING      : ('a'..'z'|'A'..'Z')+;
INTEGER     : '0'..'9'+;
ELEMENTS    : value | value ',' ELEMENTS;

When I try to generate the code using ANTLRWorks, I get the following Exception:

error (211): Grammar.g.1:8: [fatal] rule Tokens has non-LL(*) decision due to recursive rule  invocations reacable from alts 18,24. Resolve by left-factoring or using syntactic predicates or using backtrack=true option

I had a look at the following website:

http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar

Any suggestions what can be done? I couldn't find much online.

When I add the following:

 grammar Grammar;

@options {
  backtrack=true;
}

I get only one Exception:

    error(100): Grammar.g:3:2: syntax error: antlr: NoViableAltException(55@[])
   [12:03:20] error(100): Grammar.g:3:2: syntax error: antlr: MissingTokenException (inserted [@-1,0:0='<missing ACTION>',<50>,3:1] at options {)
   [12:03:20] error(100): Grammar.g:3:2: syntax error: antlr:    org.antlr.runtime.EarlyExitException
 [12:03:20] error(150):  grammar file Grammar.g has no rules
  [12:03:20] error(100): Grammar.g:0:1: syntax error: assign.types:   MismatchedTreeNodeException(0!=3)

EDIT:

I have added value and ELEMENTS. When using ELEMENTS inside the graph in ANTLRWorks, the value cannot be seen. I can only see:

',' ELEMENTS

instead of:

value | value ',' ELEMENTS

Could this be the cause of the problem for the Tokens Exception? Is this actually allowed? What is the solution?

Answer 1

try

query           : (STATEMENT)*;

a couple of advices:

• avoid rules like

   value | value ',' ELEMENTS 

where both alternative starts with the same term. Move that term "out of brackets":

   value (','  value ) * 

• all terms must be defined (NUMBER is not defined in your grammar)

• only one rule can define term which is not referenced from other rules