简单的 ANTLR 错误
我从 ANTLR 开始，但出现了一些错误，我真的不明白为什么。
这是我非常简单的语法
grammar Expr;
options {backtrack=true;}
@header {}
@members {}
expr returns [String s]
: (LETTER SPACE DIGIT | TKDC) {$s = $DIGIT.text + $TKDC.text;}
;
// TOKENS
SPACE : ' ' ;
LETTER : 'd' ;
DIGIT : '0'..'9' ;
TKDC returns [String s] : 'd' SPACE 'C' {$s = "d C";} ;
这是JAVA源代码，我只要求“expr”结果：
import org.antlr.runtime.*;
class Testantlr {
public static void main(String[] args) throws Exception {
ExprLexer lex = new ExprLexer(new ANTLRFileStream(args[0]));
CommonTokenStream tokens = new CommonTokenStream(lex);
ExprParser parser = new ExprParser(tokens);
try {
System.out.println(parser.expr());
} catch (RecognitionException e) {
e.printStackTrace();
}
}
}
当我的输入文件具有以下内容d 9时，问题就出现了。
我收到以下错误：
x line 1:2 mismatched character '9' expecting 'C'
x line 1:3 no viable alternative at input '<EOF>'
有人知道这里的问题吗？
I'm starting with ANTLR, but I get some errors and I really don't understand why.
Here you have my really simple grammar
grammar Expr;
options {backtrack=true;}
@header {}
@members {}
expr returns [String s]
: (LETTER SPACE DIGIT | TKDC) {$s = $DIGIT.text + $TKDC.text;}
;
// TOKENS
SPACE : ' ' ;
LETTER : 'd' ;
DIGIT : '0'..'9' ;
TKDC returns [String s] : 'd' SPACE 'C' {$s = "d C";} ;
This is the JAVA source, where I only ask for the "expr" result:
import org.antlr.runtime.*;
class Testantlr {
public static void main(String[] args) throws Exception {
ExprLexer lex = new ExprLexer(new ANTLRFileStream(args[0]));
CommonTokenStream tokens = new CommonTokenStream(lex);
ExprParser parser = new ExprParser(tokens);
try {
System.out.println(parser.expr());
} catch (RecognitionException e) {
e.printStackTrace();
}
}
}
The problem comes when my input file has the following content d 9.
I get the following error:
x line 1:2 mismatched character '9' expecting 'C'
x line 1:3 no viable alternative at input '<EOF>'
Does anyone knwos the problem here?
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评论（1）
您的语法有一些问题：
options部分中的backtrack=true并不适用于词法分析器规则，这就是为什么您会得到不匹配的字符 '9' 期望 ' C'（没有回溯！）；expr规则的内容：(LETTER SPACE DIGIT | TKDC) {$s = $DIGIT.text + $TKDC.text;}没有多大意义（大部头书）。您想要匹配LETTER SPACE DIGIT或TKDC，但您试图获取这两个选项的text：$DIGIT .text和$TKDC.text。在我看来，
TKDC需要“升级”为解析器规则。我认为您简化了您的示例，无法说明您所面临的问题。也许更好的主意是解释你的实际问题：你想准确解析什么？
There are a few things wrong with your grammar:
Tokens, soreturns [String s]is ignored afterTKDC;backtrack=truein youroptionssection does not apply to lexer rules, that is why you getmismatched character '9' expecting 'C'(no backtracking there!);exprrule:(LETTER SPACE DIGIT | TKDC) {$s = $DIGIT.text + $TKDC.text;}doesn't make much sense (to me). You either want to matchLETTER SPACE DIGITorTKDC, yet you're trying to grab thetextof both choices:$DIGIT.textand$TKDC.text.It looks to me
TKDCneeds to be "promoted" to a parser rule instead.I think you dumbed down your example a bit too much to illustrate the problem you were facing. Perhaps it's a better idea to explain your actual problem instead: what are you trying to parse exactly?