编写没有语法文件的自定义 Xtext/ANTLR 词法分析器 [英] Writing a custom Xtext/ANTLR lexer without a grammar file

问题描述

我正在为 CoffeeScript 编写一个 Eclipse/Xtext 插件，我意识到我可能需要手动为它编写一个词法分析器.CoffeeScript 解析器还使用 手写词法分析器处理语法中的缩进和其他技巧.

I'm writing an Eclipse/Xtext plugin for CoffeeScript, and I realized I'll probably need to write a lexer for it by hand. CoffeeScript parser also uses a hand-written lexer to handle indentation and other tricks in the grammar.

Xtext 生成一个扩展 org.eclipse.xtext.parser.antlr.Lexer 的类，而后者又扩展了 org.antlr.runtime.Lexer.所以我想我会延长它.我可以看到两种方法来做到这一点

Xtext generates a class that extends org.eclipse.xtext.parser.antlr.Lexer which in turn extends org.antlr.runtime.Lexer. So I suppose I'll have extend it. I can see two ways to do that

• 覆盖mTokens().这是由生成的代码完成的，更改内部状态.
• 覆盖 nextToken() 这似乎是一种自然的方法，但我必须跟踪内部状态.

• Override mTokens(). This is done by the generated code, changing the internal state.
• Override nextToken() which seems a natural approach, but then I'll have to keep track of the internal state.

我找不到任何示例，如何在没有语法文件的情况下为 ANTLR 编写一个简单的词法分析器.所以最简单的答案是指向一个.

I couldn't find any example how to write even a simple lexer for ANTLR without a grammar file. So the easiest answer would be a pointer to one.

Xtext 的答案:具有重要/语义空白的语言的语法 指的是处理缩进问题的 todotext通过更改底层输入流中的标记.我不想走那条路，因为处理咖啡脚本语法的其他技巧会很困难.

An answer to Xtext: grammar for language with significant/semantic whitespace refers to todotext which handles the problem of indentation by changing the tokens in the underlying input stream. I don't want to go that way, because it would be difficult to handle other tricks of the coffeescript grammar.

更新:

同时我意识到我的问题部分是针对 Xtext 的.

I realized in the meantime that my question was partly Xtext specific.

推荐答案

这是我所做的 - 并且有效.

Here is what I did -- and it works.

public class MyLexer extends myprj.parser.antlr.internal.InternalMylangLexer {
  private SomeExternalLexer externalLexer;

  public Lexer(CharStream in) {
    super(in);
    externalLexer = new SomeExternalLexer(in);
  }

  @Override
  public Token nextToken() {
    Token token = null;
    ExternalToken extToken = null;
    try {
      extToken = externalLexer.nextToken();
      if (extToken == null) {
        token = CommonToken.INVALID_TOKEN;
      }
      else {
        token = mapExternalToken(extToken);
      }
    }
    catch (Exception e) {
      token = CommonToken.INVALID_TOKEN;
    }
    return token;
  }

  protected Token mapExternalToken(ExternalToken extToken) {
    // ...
  }
}

然后我有一个稍微定制的解析器，其中包含:

Then I have a slightly customized parser containing:

public class BetterParser extends MylangParser {
  @Override
  protected TokenSource createLexer(CharStream stream) {
    MyLexer lexer = new MyLexer(stream);
    return lexer;
  }
}

我还必须更改我的 MylangRuntimeModule.java 以包含此方法

I also had to change my MylangRuntimeModule.java to contain this method

@Override
public Class<? extends org.eclipse.xtext.parser.IParser> bindIParser() {
     return myprj.parser.BetterParser.class ;
}

就是这样.

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