处理以空格开头的字符串 [英] Handle strings starting with whitespaces

问题描述

我正在尝试使用以下规则集创建ANTLR v4语法:

I'm trying to create an ANTLR v4 grammar with the following set of rules:

1.如果一行以@开头，则被视为标签:

1.In case a line starts with @, it is considered a label:

@label

2.如果该行以cmd开头，则将其视为命令

2.In case the line starts with cmd, it is treated as a command

cmd param1 param2
 

3.如果一行以空格开头，则将其视为字符串.所有文本都应被提取.字符串可以是多行，因此它们以空行结尾

3.If a line starts with a whitespace, it is considered a string. All the text should be extracted. Strings can be multiline, so they end with an empty line

 A long string with multiline support
 and any special characters one can imagine.
<-empty line here->
    

4.最后，如果一行以空格( @ 和 cmd )以外的任何内容开头，则应将第一个单词视为标题.

4.Lastly, in case a line starts with anything but whitespace, @ and cmd, it's first word should be considered a heading.

Heading A long string with multiline support
 and any special characters one can imagine.
<-empty line here->
    

处理标签和命令很容易.但是我对字符串和标题一无所知.无论doubleNewline 和 doublenewline 为何，分隔 whitespace单词空白的最佳方法是什么?我已经看到了很多带有空格的示例，但是它们都不能用于随机文本和换行符.我不希望您为我编写实际的代码.建议一种方法.

It was easy to handle lables and commands. But I am clueless about strings and headings. What is the best way to separate whitespace word whitespace whatever doubleNewline and whatever doubleNewline? I've seen a lot of samples with whitespaces, but none of them works with both random text and newlines. I don't expect you to write actual code for me. Suggesting an approach will do.

推荐答案

这种方法应该可以解决问题:

Something like this should do the trick:

lexer grammar DemoLexer;

LABEL
 : '@' [a-zA-Z]+
 ;

CMD
 : 'cmd' ~[\r\n]+
 ;

STRING
 : ' ' .*? NL NL
 ;

HEADING
 : ( ~[@ \t\r\nc] | 'c' ~'m' | 'cm' ~'d' ).*? NL NL
 ;

SPACE
 : [ \t\r\n] -> skip
 ;

OTHER
 : .
 ;

fragment NL
 : '\r'? '\n'
 | '\r'
 ;

这并不强制要求行的开始".要求.如果这是您想要的内容，则必须在语法中添加语义谓词，然后将其与目标语言联系起来.对于Java，看起来像这样:

This does not mandate the "beginning of the line" requirement. If that is something you want, you'll have to add semantic predicates to your grammar, which ties it to a target language. For Java, that would look like this:

LABEL
 : {getCharPositionInLine() == 0}? '@' [a-zA-Z]+
 ;

请参阅:

• ANTLR4中的语义谓词?
• https://github.com/antlr/antlr4/blob/master/doc/predicates.md

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