Antlr4 - 是否有使用 ParseTree Walker 的简单示例? [英] Antlr4 - Is there a simple example of using the ParseTree Walker?

问题描述

Antlr4 有一个新类 ParseTreeWalker.但是我该如何使用它呢?我正在寻找一个最小的工作示例.我的语法文件是gram.g4"，我想解析一个文件program.txt"

Antlr4 has a new class ParseTreeWalker. But how do I use it? I am looking for a minimal working example. My grammar file is 'gram.g4' and I want to parse a file 'program.txt'

到目前为止，这是我的代码.(这假设 ANTLR 已经运行了我的语法文件并创建了所有的 gramBaseListener、gramLexer 等):

Here is my code so far. (This assumes ANTLR has run my grammar file and created all of the gramBaseListener, gramLexer, etc etc):

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
import static org.antlr.v4.runtime.CharStreams.fromFileName;

public class launch{
public static void main(String[] args) {

    CharStream cs = fromFileName("gram.g4");  //load the file
    gramLexer lexer = new gramLexer(cs);  //instantiate a lexer
    CommonTokenStream tokens = new CommonTokenStream(lexer); //scan stream for tokens
    gramParser parser = new gramParser(tokens);  //parse the tokens

    // Now what??  How do I connect the above with the below? 

    ParseTreeWalker walker = new ParseTreeWalker();  // how do I use this to parse program.txt??
}}

我使用的是 java，但我认为它在其他语言中也类似.

I am using java but I assume it is similar in other languages.

ANTLR 文档(http://www.antlr.org/api/Java/index.html) 缺少示例.网上有很多教程，但大多是针对ANTLR 3版本的.少数使用版本4的不工作或过时(例如，没有parser.init()函数，像ANTLRInputStream这样的类被贬值)

The ANTLR documentation (http://www.antlr.org/api/Java/index.html) is short on examples. There are many tutorials on the internet but they are mostly for ANTLR version 3. The few using version 4 don't work or are outdated (for example, there is no parser.init() function, and classes like ANTLRInputStream are depreciated)

提前感谢任何可以提供帮助的人.

Thanks in advance for anyone who can help.

推荐答案

对于语法中的每条解析器规则，生成的解析器都会有一个具有该名称的对应方法.调用该方法将按照该规则开始解析.

For each of your parser rules in your grammar the generated parser will have a corresponding method with that name. Calling that method will start parsing at that rule.

因此，如果您的根规则"被命名为 start，那么您将通过返回 ParseTree 的 gramParser.start() 开始解析>.然后可以将此树与您要使用的侦听器一起输入 ParseTreeWalker.

Therefore if your "root-rule" is named start then you'd start parsing via gramParser.start() which returns a ParseTree. This tree can then be fed into the ParseTreeWalker alongside with the listener you want to be using.

总而言之，它看起来像这样(由 OP 编辑​​):

All in all it could look something like this (EDITED BY OP):

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
import static org.antlr.v4.runtime.CharStreams.fromFileName;

public class launch{
public static void main(String[] args) {

    CharStream cs = fromFileName("program.txt");  //load the file
    gramLexer lexer = new gramLexer(cs);  //instantiate a lexer
    CommonTokenStream tokens = new CommonTokenStream(lexer); //scan stream for tokens
    gramParser parser = new gramParser(tokens);  //parse the tokens

    ParseTree tree = parser.start(); // parse the content and get the tree
    Mylistener listener = new Mylistener();

    ParseTreeWalker walker = new ParseTreeWalker();
    walker.walk(listener,tree);
}}

************ 新文件 Mylistener.java ************

************ NEW FILE Mylistener.java ************

public class Mylistener extends gramBaseListener {
        @Override public void enterEveryRule(ParserRuleContext ctx) {  //see gramBaseListener for allowed functions
            System.out.println("rule entered: " + ctx.getText());      //code that executes per rule
        }
    }

当然你必须用你的 BaseListener 实现替换

Of course you have to replace <listener> with your implementation of BaseListener

还有一个小的 sidenode:在 Java 中，类名以大写字母开头是一种惯例，我建议您坚持这样做，以使代码对其他人更具可读性.

And just one small sidenode: In Java it is convention to start classnames with capital letters and I'd advise you to stick to that in order for making the code more readable for other people.

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