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POAntlr Left-Factoring Grammar
 

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  1. POAntlr Left-Factoring Grammar
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    <p>I am new to Antlr. I am defining a grammar for my company using Antlr 3.</p> <p>Below is my grammar:</p> <pre><code>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; </code></pre> <p>When I try to generate the code using ANTLRWorks, I get the following Exception:</p> <pre><code>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 </code></pre> <p>I had a look at the following website:</p> <p><a href="http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar" rel="nofollow">http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar</a></p> <p>Any suggestions what can be done? I couldn't find much online.</p> <p>When I add the following:</p> <pre><code> grammar Grammar; @options { backtrack=true; } </code></pre> <p>I get only one Exception:</p> <pre><code> 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='&lt;missing ACTION&gt;',&lt;50&gt;,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) </code></pre> <p>EDIT:</p> <p>I have added value and ELEMENTS. When using ELEMENTS inside the graph in ANTLRWorks, the value cannot be seen. I can only see:</p> <pre><code>',' ELEMENTS </code></pre> <p>instead of:</p> <pre><code>value | value ',' ELEMENTS </code></pre> <p>Could this be the cause of the problem for the Tokens Exception? Is this actually allowed? What is the solution?</p>
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