如何在 antlr4 中报告语法歧义 [英] how to report grammar ambiguity in antlr4

问题描述

根据antlr4 book(第159页)，使用语法Ambig.g4，可以通过以下方式报告语法歧义:

According to the antlr4 book (page 159), and using the grammar Ambig.g4, grammar ambiguity can be reported by:

grun Ambig stat -diagnostics

或等效地，以代码形式:

or equivalently, in code form:

parser.removeErrorListeners();
parser.addErrorListener(new DiagnosticErrorListener());
parser.getInterpreter().setPredictionMode(PredictionMode.LL_EXACT_AMBIG_DETECTION);

grun 命令使用 antlr-4.5.3 为我正确报告歧义.但是当我使用代码表单时，我没有得到歧义报告.这是命令跟踪:

The grun command reports the ambiguity properly for me, using antlr-4.5.3. But when I use the code form, I dont get the ambiguity report. Here is the command trace:

$ antlr4 Ambig.g4   # see the book's page.159 for the grammar
$ javac Ambig*.java
$ grun Ambig stat -diagnostics < in1.txt # in1.txt is as shown on page.159
    line 1:3 reportAttemptingFullContext d=0 (stat), input='f();'
    line 1:3 reportAmbiguity d=0 (stat): ambigAlts={1, 2}, input='f();'
$ javac TestA_Listener.java
$ java TestA_Listener < in1.txt   # exits silently

TestA_Listener.java 代码如下:

The TestA_Listener.java code is the following:

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.atn.*; // for PredictionMode
import java.util.*;
public class TestA_Listener {
    public static void main(String[] args) throws Exception {
        ANTLRInputStream input = new ANTLRInputStream(System.in);
        AmbigLexer lexer = new AmbigLexer(input);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        AmbigParser parser = new AmbigParser(tokens);
        parser.removeErrorListeners(); // remove ConsoleErrorListener
        parser.addErrorListener(new DiagnosticErrorListener());
        parser.getInterpreter().setPredictionMode(PredictionMode.LL_EXACT_AMBIG_DETECTION);
        parser.stat();
    }
}

谁能指出上面的java代码应该如何修改，以打印歧义报告?

Can somebody please point out how the above java code should be modified, to print the ambiguity report?

为了完整起见，这里是代码 Ambig.g4 :

For completeness, here is the code Ambig.g4 :

语法歧义；

stat: expr ';'        // expression statement
    | ID '(' ')' ';'  // function call statement
    ;

expr: ID '(' ')'
    | INT
    ;

INT :   [0-9]+ ;
ID  :   [a-zA-Z]+ ;
WS  :   [ \t\r\n]+ -> skip ;

这里是输入文件 in1.txt :

And here is the input file in1.txt :

f();

推荐答案

我等了好几天才让其他人发布他们的答案.经过几轮实验，终于找到了答案:

I waited for several days for other people to post their answers. Finally after several rounds of experimenting, I found an answer:

应从上面的代码中删除以下行.然后我们得到与 grun 给出的相同的歧义报告.

The following line should be deleted from the above code. Then we get the same ambiguity report as given by grun.

parser.removeErrorListeners(); // remove ConsoleErrorListener

这篇关于如何在 antlr4 中报告语法歧义的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！