CODEWITHSUNDEEP
javaparsingantlr4
Pratik
Pratik

Reputation: 988

ANTRL4 is parsing incorrectly

While learning ANTRL4 I tried to parse very basic pattern, which can have one or more digits.

Abc.g4

grammar Abc;

@header {
    package antlr4;
}

fragment DIGIT : [0-9]+;

log : DIGIT;

Main method

public class OwnParser extends AbcBaseListener
{


    public static void main(String args[])
    {
        String javaClassContent = "9";
        AbcLexer abcLexer = new AbcLexer(CharStreams.fromString(javaClassContent));

        CommonTokenStream tokens = new CommonTokenStream(abcLexer);
        AbcParser parser = new AbcParser(tokens);

         ParseTree tree = parser.log();

        ParseTreeWalker walker = new ParseTreeWalker();
        OwnParser listener= new OwnParser();

        walker.walk(listener, tree);
    }
}

But when I execute this, it says:

line 1:0 token recognition error at: '9'

line 1:1 missing DIGIT at ''

rule entered: <missing DIGIT>

Am I missing something ?

Upvotes: 0

Views: 87

Answers (1)

sepp2k
sepp2k

Reputation: 370455

You get an error on the input 9 because you didn't define any lexer rule that matches 9. In fact, you didn't define any lexer rules at all. Note that you defined DIGIT as a fragment only and fragments don't produce tokens.

You should also have gotten a warning "implicit definition of token DIGIT in parser" in your grammar.

If you remove the fragment keyword from the definition of DIGIT, both of those problems will go away.

Upvotes: 2

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