ANTLR4:lexer命令中无法识别的常数值 [英] ANTLR4: Unrecognized constant value in a lexer command

问题描述

我正在学习如何使用更多" lexer命令.我输入了ANTLR书第281页中显示的词法分析器语法:

I am learning how to use the "more" lexer command. I typed in the lexer grammar shown in the ANTLR book, page 281:

lexer grammar Lexer_To_Test_More_Command ;

LQUOTE : '"'        -> more, mode(STR) ;

WS   : [ \t\r\n]+   -> skip ; 

mode STR ;

STRING : '"'    -> mode(DEFAULT_MODE) ;

TEXT : .        -> more ;

然后，我创建了这个简单的解析器以使用词法分析器:

Then I created this simple parser to use the lexer:

grammar Parser_To_Test_More_Command ;

import Lexer_To_Test_More_Command ;

test: STRING EOF ;

然后我打开DOS窗口并输入以下命令:

Then I opened a DOS window and entered this command:

antlr4 Parser_To_Test_More_Command.g4

产生此警告消息:

警告(155):Parser_To_Test_More_Command.g4:3:29:规则LQUOTE 包含一个无法识别的常数值的lexer命令；词法分析器 口译员可能会产生错误的输出结果

warning(155): Parser_To_Test_More_Command.g4:3:29: rule LQUOTE contains a lexer command with an unrecognized constant value; lexer interpreters may produce incorrect output

我在词法分析器或解析器中做错什么了吗?

Am I doing something wrong in the lexer or parser?

推荐答案

组合语法(即仅以grammar开头的语法，而不是parser grammar或lexer grammar开头的语法)不能使用词法分析器模式.代替使用import功能¹，您应该使用这样的tokenVocab功能:

Combined grammars (which are grammars that start with just grammar, instead of parser grammar or lexer grammar) cannot use lexer modes. Instead of using the import feature¹, you should use the tokenVocab feature like this:

Lexer_To_Test_More_Command.g4 :

lexer grammar Lexer_To_Test_More_Command;

// lexer rules and modes here

Parser_To_Test_More_Command.g4 :

parser grammar Parser_To_Test_More_Command;

options {
  tokenVocab = Lexer_To_Test_More_Command;
}

// parser rules here

¹我实际上建议在ANTLR中完全避免使用import语句.我上面描述的方法几乎总是首选.

¹ I actually recommend avoiding the import statement altogether in ANTLR. The method I described above is almost always preferable.

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