需要Antlr多余谓词吗? [英] Antlr superfluous Predicate required?
问题描述
我有一个要忽略其中一部分的文件.在Lexer中,我使用门控语义谓词来避免为文件的不感兴趣部分创建令牌.我的规则类似于以下内容.
I have a file where I want to ignore parts of it. In the Lexer I use gated semantic predicates to avoid creating tokens for the uninteresting part of the file. My rules are similar to the following.
A
: {!ignore}?=> 'A'
;
START_IGNORE
: 'foo' {ignore = true; skip();}
;
END_IGNORE
: 'oof' {ignore = false; skip();}
;
IGNORE
: {ignore}?=> . {skip();}
;
但是,除非我将START和END更改为也使用语义谓词(如下所示),否则它将不起作用.
However unless I change START and END to also use semantic predicates (as below) it does not work..
A
: {!ignore}?=> 'A'
;
START_IGNORE
: {true}?=> 'foo' {ignore = true; skip();}
;
END_IGNORE
: {true}?=> 'oof' {ignore = false; skip();}
;
IGNORE
: {ignore}?=> . {skip();}
;
为什么必须添加谓词?
我正在使用antlr-3.4
I am using antlr-3.4
推荐答案
为什么必须添加谓词?
Why do I have to add the predicates?
你不知道.至少不使用ANTLR v3.3.我不知道您正在测试的方法是什么,但是请不要使用ANTLRWorks的解释器或Eclipse ANTLR IDE插件.始终从命令行进行一些测试.
You don't. At least, not using ANTLR v3.3. I don't know how exactly you're testing, but don't use ANTLRWorks' interpreter or the Eclipse ANTLR IDE plugin. Always do a little test from the command line.
grammar T;
@parser::members {
public static void main(String[] args) throws Exception {
TLexer lexer = new TLexer(new ANTLRStringStream("A foo A B C oof A"));
TParser parser = new TParser(new CommonTokenStream(lexer));
parser.parse();
}
}
@lexer::members {
private boolean ignore = false;
}
parse
: (t=.
{System.out.printf("[\%02d] type=\%s text='\%s'\n", $t.getCharPositionInLine(), tokenNames[$t.type], $t.text);}
)* EOF
;
A
: {!ignore}?=> 'A'
;
START_IGNORE
: 'foo' {ignore = true; skip();}
;
END_IGNORE
: 'oof' {ignore = false; skip();}
;
IGNORE
: {ignore}?=> . {skip();}
;
SPACE
: ' ' {skip();}
;
像这样运行它:
java -cp antlr-3.3.jar org.antlr.Tool T.g
javac -cp antlr-3.3.jar *.java
java -cp .:antlr-3.3.jar TParser
将打印以下内容:
[00] type=A text='A'
[16] type=A text='A'
即:从输入"A foo A B C oof A"
中输入以下内容:"foo A B C oof"
被踩skip
.
I.e.: from the input "A foo A B C oof A"
the following: "foo A B C oof"
is skip
ped.
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