JavaCC语法 - 适当的lexing

时间:2014-02-21 14:57:45

标签: javacc

我有一个JavaCC语法,其定义如下:

<REGULAR_IDENTIFIER : (["A"-"Z"])+ > // simple identifier like say "DODGE"
<_LABEL : (["A"-"Z"])+ (":") > // label, eg "DODGE:"
<DOUBLECOLON : "::">
<COLON : ":">

现在“DODGE ::”lexed为<_LABEL> <COLON>(“DODGE:”“:”) 但我需要把它当作<REGULAR_IDENTIFIER> <DOUBLECOLON>(“DODGE”“::”)

2 个答案:

答案 0 :(得分:1)

我认为以下内容可行

MORE: { < (["A"-"Z"])+ :S0 > } // Could be identifier or label.
<S0> TOKEN: { <LABEL : ":" : DEFAULT> } // label, eg "DODGE:"
<S0> TOKEN: { <IDENTIFIER : "" : DEFAULT > } // simple identifier like say "DODGE"
<S0> TOKEN: { <IDENTIFIER : "::" { matchedToken.image = image.substring(0,image.size()-2) ; } : S1 > }
<S1> TOKEN: { <DOUBLECOLON : "" { matchedToken.image =  "::" ; } : DEFAULT> }
<DOUBLECOLON : "::">
<COLON : ":">

请注意,“DODGE :::”是三个令牌,而不是两个。

答案 1 :(得分:0)

在javacc中使用最大匹配规则(最长前缀匹配规则),请参阅: http://www.engr.mun.ca/~theo/JavaCC-FAQ/javacc-faq-moz.htm#more-than-one

这意味着_LABEL标记将在REGULAR_IDENTIFIER标记之前匹配,因为_LABEL标记将包含更多字符。这意味着你不应该在tokenizer中完成你想要做的事情。

我编写了一个正确识别语法的解析器,我使用解析器来识别_LABEL,而不是识别器:

options {
    STATIC = false;
}

PARSER_BEGIN(Parser)

import java.io.StringReader;

public class Parser {

    //Main method, parses the first argument to the program
    public static void main(String[] args) throws ParseException {
        System.out.println("Parseing: " + args[0]);
        Parser parser = new Parser(new StringReader(args[0]));
        parser.Start();
    }
}

PARSER_END(Parser)

//The _LABEL will be recognized by the parser, not the tokenizer
TOKEN :
{
    <DOUBLECOLON : "::"> //The double token will be preferred to the single colon due to the maximal munch rule
    |
    <COLON : ":">
    |
    <REGULAR_IDENTIFIER : (["A"-"Z"])+ > // simple identifier like say "DODGE"
}

/** Root production. */
void Start() :
{}
{
    ( 
        LOOKAHEAD(2) //We need a lookahead of two, to see if this is a label or not
        <REGULAR_IDENTIFIER> <COLON> { System.err.println("label"); } //Labels, should probably be put in it's own production
        | <REGULAR_IDENTIFIER> { System.err.println("reg_id"); }  //Regulair identifiers
        | <DOUBLECOLON> { System.err.println("DC"); } 
        | <COLON> { System.err.println("C"); } 
    )+
}

实际上,您应该将<REGULAR_IDENTIFIER> <COLON>移至_label作品。

希望它有所帮助。