ANTLR4模棱两可的语法 [英] ANTLR4 ambiguous grammar
问题描述
我想要实现以下行为:User:class应该被解析为Object - User; Type - class，Us:er:class也应该得到Object - Us:er; Type - class.我不能使第二部分起作用，一旦我添加:作为WORD的合法符号，它就会将整个输入解析为对象Object - Us:er:class.
我的语法:
I want to achieve following behavior: User:class should be parsed to Object - User; Type - class, alsoUs:er:class should result Object - Us:er; Type - class. I can't make second part work, as soon as I add : as a legal symbol for WORD it parses whole input as an object Object - Us:er:class.
My grammar:
grammar Sketch;
/*
* Parser Rules
*/
input : (object)+ EOF ;
object : objectName objectType? NEWLINE ;
objectType : ':' TYPE ;
objectName : WORD ;
/*
* Lexer Rules
*/
fragment LOWERCASE : [a-z] ;
fragment UPPERCASE : [A-Z] ;
fragment NUMBER : [0-9] ;
fragment WHITESPACE : (' ') ;
fragment SYMBOLS : [!-/:-@[-`] ;
fragment C : [cC] ;
fragment L : [lL] ;
fragment A : [aA] ;
fragment S : [sS] ;
fragment T : [tT] ;
fragment U : [uU] ;
fragment R : [rR] ;
TYPE : ((C L A S S) | (S T R U C T));
NEWLINE : ('\r'? '\n' | '\r')+ ;
WORD : (LOWERCASE | UPPERCASE | NUMBER | WHITESPACE | SYMBOLS)+ ;
每个字母的片段用于不区分大小写的解析. 据我了解，词法分析器从上到下优先考虑规则，因此TYPE应该优先于WORD，但我无法实现. 我是antlr4的新手，也许我错过了明显的东西.
Fragments for each letter are for case-insensitive parsing. As I understand, lexer gives priority to rules top-to-bottom, so TYPE should be picked over WORD, but I can't achieve it. I'm new to antlr4, maybe I'm missing something obvious.
推荐答案
如果您只需要解析这么简单的内容，则无需使用ANTLR编写解析器.这是我建议仅使用简单正则表达式的极少数情况之一. 如果您想用ANTLR解决它，我会这样做: 1)丑陋的解决方案:您尝试使用谓词或动作来欺骗&强迫解析做你想做的事 2)您只需定义两个标记:一个用于获取标识符，另一个用于获取分号.然后，稍后使用解析器在代码中进行合成.
If you just need to parse something so simple you do not need to write a parser with ANTLR. It is one of the very few cases where I would suggest just using a simple regex. If you want to solve it with ANTLR I would do it like this: 1) Ugly solution: you try to use predicates or actions to trick & force the parsing to do what you want 2) You simply define two tokens: one to get identifiers and one to get the semicolon. Then you do the composition later, in the code using your parser.
例如，对于User:class，您将获得[[ID:"User"]，[ID:"class"]]
而对于Us:er:class，您将获得[[ID:"Us"]，[ID:"er"]，[ID:"class"]]
那么您编码后就知道最后一个ID代表类型，所有其他ID的顺序代表对象.
For example, for User:class you would get [[ID:"User"], [ID:"class"]]
while for Us:er:class you would get [[ID:"Us"], [ID:"er"], [ID:"class"]]
then you code you know that the last ID represent the type and the sequence of all the other IDs represent the object.
都不是很好的解决方案，但我认为ANTLR不是您要尝试做的正确工具.
Neither are not great solutions but I think ANTLR is not the right tool for what you are trying to do.
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