您可以通过实现 ParseTreeVisitor 接口来创建解析树遍历器.为方便使用，可以在编译语法时指定 Antlr 生成基本访问者(在 Antlrworks 中，Run->Generate Recognizer->Next->Generate Visitor->Next->Finish代码>).基本访问者将被称为 MyGrammarBaseVisitor.请注意，访问者有一个泛型类型 T，每个访问方法都应返回该类型.我建议使用 Void 进行手动操作，或者使用 String 以便在代码生成过程中使用.

You can create a parse tree walker by implementing the ParseTreeVisitor interface. For ease of use, you can specify Antlr to generate a base visitor when compiling the grammar (in Antlrworks, Run->Generate Recognizer->Next->Generate Visitor->Next->Finish). The base visitor will be called MyGrammarBaseVisitor. Note that the visitor has a generic type T, which every single visit method should return. I recommend using Void for manual manipulation or String for ease of use during code generation.

在扩展基本访问者之后(我假设我们在这里处理String)，您需要覆盖访问方法.这些方法以您拥有的语法规则命名.这些方法中的每一个都将接收一个 ParserContext ctx 参数，您可以使用它来访问子规则和/或获取终端值.例如，您可以这样做:

After you extend the base visitor (I'll assume here we're dealing with String), you need to override the visit methods. These methods are named after the grammar rules you have. Each of these methods will receive a ParserContext ctx parameter, which you use to visit child rules and/or get terminal values. For example, you could do this:

class MyVisitor extends MyGrammarBaseVisitor<String> {
    @Override
    public String visitMultiplicative(MyGrammarParser.MultiplicativeContext ctx) {
        if (ctx.opMult().getText().equals("/")) return "\\frac{" + visit(ctx.expr(0)) + "}{" + visit(ctx.expr(1)) + "}";
        else return visit(ctx.expr(0)) + "\\cdot " + visit(ctx.expr(1));
    }
    // visit methods for other rules...
}

我假设你的 multiplicative 规则看起来像 multiplicative: expr opMult expr;opMult: '*' |'/'; 您可以在 The Definitive Antlr 中找到更多信息4 参考.您还可以在 Antlr 文档 中找到更多信息和示例.

I'm assuming your multiplicative rule looks like multiplicative: expr opMult expr; opMult: '*' | '/'; You can find more information in The Definitive Antlr 4 Reference. You may also find more information and examples in the Antlr documentation.