在ANTLR的3C令牌的返回值 [英] Token return values in ANTLR 3 C

问题描述

我是新来ANTLR，而我试图写用C语言的目标（antler3C）一个简单的解析器。语法很简单，我想有每个规则返回一个值，例如：

I'm new to ANTLR, and I'm attempting to write a simple parser using C language target (antler3C). The grammar is simple enough that I'd like to have each rule return a value, eg:

number returns [long value]
 :
 ( INT {$value = $INT.ivalue;}
 | HEX {$value = $HEX.hvalue;}
 ) 
 ; 

HEX returns [long hvalue] 
    : '0' 'x' ('0'..'9'|'a'..'f'|'A'..'F')+  {$hvalue = strtol((char*)$text->chars,NULL,16);}
    ;

INT returns [long ivalue] 
    : '0'..'9'+    {$ivalue = strtol((char*)$text->chars,NULL,10);}
    ;

每个规则收集它的返回值是孩子的规则，直到最顶端的规则返回一个很好的结构充满我的数据。

Each rule collects the return value of it's child rules until the topmost rule returns a nice struct full of my data.

据我所知，ANTLR允许词法规则（令牌，例如'INT'和;HEX）返回值一样的语法规则（例如'号'）。然而，生成的C code将不能编译：

As far as I can tell, ANTLR allows lexer rules (tokens, eg 'INT' & 'HEX') to return values just like parser rules (eg 'number'). However, the generated C code will not compile:

error C2228: left of '.ivalue' must have class/struct/union
error C2228: left of '.hvalue' must have class/struct/union

我做了一些闲逛，和错误意义 - 令牌最终成为通用ANTLR3_COMMON_TOKEN_struct，它不允许返回值。所以，也许Ç目标只是不支持此功能。但是就像我说的，我是新来这个，我去哈林去寻找另一种方法，我想确认，我不能做这种方式了。

I did some poking around, and the errors make sense - the tokens end up as generic ANTLR3_COMMON_TOKEN_struct, which doesn't allow for a return value. So maybe the C target just doesn't support this feature. But like I said, I'm new to this, and before I go haring off to find another approach I want to confirm that I can't do it this way.

所以，问题是这样的：是否antler3C支持返回值词法规则，若然是使用它们的正确方法？

So the question is this: 'Does antler3C support return values for lexer rules, and if so what is the proper way to use them?'

推荐答案

不是真的任何新信息，只是在什么@bemace已经提到了一些细节。

Not really any new information, just some details on what @bemace already mentioned.

没有，词法规则不能有返回值。请参阅 4.3规则 权威ANTLR参考：

No, lexer rules cannot have return values. See 4.3 Rules from The Definitive ANTLR reference:

就像函数调用，ANTLR解析器和树解析器规则可以有
  参数和返回值。 ANTLR词法规则不能有回报
  值[...]

Rule Arguments and Return Values

Just like function calls, ANTLR parser and tree parser rules can have arguments and return values. ANTLR lexer rules cannot have return values [...]

有两种选择：

您可以做转换到长在解析器规则数量：

You can do the transforming to a long in the parser rule number:

number returns [long value]
  :  INT {$value = Long.parseLong($INT.text);}
  |  HEX {$value = Long.parseLong($HEX.text.substring(2), 16);}
  ;

选项2

或者创建自己的令牌有，比如说，一个 toLong（）：长方法：

import org.antlr.runtime.*;

public class YourToken extends CommonToken {

  public YourToken(CharStream input, int type, int channel, int start, int stop) {
    super(input, type, channel, start, stop);
  }

  // your custom method
  public long toLong() {
    String text = super.getText();
    int radix = text.startsWith("0x") ? 16 : 10;
    if(radix == 16) text = text.substring(2);
    return Long.parseLong(text, radix);
  }
}

，并在选项{...} 头在你的语法使用此令牌并覆盖发出（）定义：令牌法在词法分析器类：

and define in the options {...} header in your grammar to use this token and override the emit(): Token method in your lexer class:

grammar Foo;

options{
  TokenLabelType=YourToken;
}

@lexer::members {
  public Token emit() {
    YourToken t = new YourToken(input, state.type, state.channel, 
        state.tokenStartCharIndex, getCharIndex()-1);
    t.setLine(state.tokenStartLine);
    t.setText(state.text);
    t.setCharPositionInLine(state.tokenStartCharPositionInLine);
    emit(t);
    return t;
  }
}

parse
  :  number {System.out.println("parsed: "+$number.value);} EOF
  ;

number returns [long value]
  :  INT {$value = $INT.toLong();}
  |  HEX {$value = $HEX.toLong();}
  ;

HEX
  :  '0' 'x' ('0'..'9'|'a'..'f'|'A'..'F')+
  ;

INT
  :  '0'..'9'+
  ;

当你生成一个解析器和词法分析器，并运行这个测试类：

When you generate a parser and lexer, and run this test class:

import org.antlr.runtime.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        ANTLRStringStream in = new ANTLRStringStream("0xCafE");
        FooLexer lexer = new FooLexer(in);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        FooParser parser = new FooParser(tokens);
        parser.parse();
    }
}

这将产生以下的输出：

it will produce the following output:

parsed: 51966

第一个选择似乎更实用于你的情况。

The first options seems the more practical in your case.

需要注意的是，你可以看到，给出的例子是Java。我不知道如果选择2在C目标/运行时支持。我决定还是发布它可以在这里用它作为日后参考上左右。

Note that, as you can see, the examples given are in Java. I have no idea if option 2 is supported in the C target/runtime. I decided to still post it to be able to use it as a future reference here on SO.

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