Antlr左因子语法 [英] Antlr Left-Factoring Grammar
问题描述
我是Antlr的新手.我正在使用Antlr 3为我的公司定义语法.
I am new to Antlr. I am defining a grammar for my company using Antlr 3.
下面是我的语法:
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;
当我尝试使用ANTLRWorks生成代码时,出现以下异常:
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
我浏览了以下网站:
http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+语法
任何建议可以做什么?我在网上找不到很多东西.
Any suggestions what can be done? I couldn't find much online.
当我添加以下内容时:
grammar Grammar;
@options {
backtrack=true;
}
我只有一个例外:
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)
我拥有增值和要素.在ANTLRWorks中的图形内部使用ELEMENTS时,无法看到该值.我只能看到:
I have added value and ELEMENTS. When using ELEMENTS inside the graph in ANTLRWorks, the value cannot be seen. I can only see:
',' ELEMENTS
代替:
value | value ',' ELEMENTS
这可能是令牌异常问题的原因吗?这是真的允许吗?解决办法是什么?
Could this be the cause of the problem for the Tokens Exception? Is this actually allowed? What is the solution?
推荐答案
尝试
query : (STATEMENT)*;
一些建议:
-
避免使用
avoid rules like
value | value ',' ELEMENTS
其中两种选择都以相同的术语开头.将该词移到方括号中:
where both alternative starts with the same term. Move that term "out of brackets":
value (',' value ) *
-
必须定义所有术语(语法中未定义NUMBER)
all terms must be defined (NUMBER is not defined in your grammar)
只有一个规则可以定义未被其他规则引用的术语
only one rule can define term which is not referenced from other rules
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