Antlr4 grammar compilation error

StackOverflow https://stackoverflow.com/questions/20762216

  •  21-09-2022
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Question

I made my own chess PGN grammar for ANTLR4, but I get a java stacktrace error :

Pgn.g4 grammar :

grammar Pgn;

file:       game (NEWLINE+ game)*;
game:       (tag+ NEWLINE+)? notation;

tag:        '['TAG_TYPE "TAG_VALUE"']';
notation: move+ END_RESULT?;
move:   MOVE_NUMBER\. MOVE_DESC MOVE_DESC       #CompleteMove
        |   MOVE_NUMBER\. MOVE_DESC             #OnlyWhiteMove
        |   MOVE_NUMBER\.\.\. MOVE_DESC         #OnlyBlackMove
        ;

END_RESULT: '1-0'
            | '0-1'
            | '1/2-1/2'
            ;

TAG_TYPE:   LETTER+;
TAG_VALUE:  .*;

MOVE_NUMBER: DIGIT+;
MOVE_DESC: .*;  

NEWLINE:    \r? \n;
SPACES:     [ \t]+ -> skip;

fragment LETTER: [a-zA-Z];
fragment DIGIT: [0-9];

And this is the error output :

$ antlr4 Pgn.g4 
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:11 required (...)+ loop did not match anything at input 'r'
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:15 mismatched tree node: n expecting <UP>
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:11 required (...)+ loop did not match anything at input 'r'
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:15 mismatched tree node: n expecting <UP>
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:11 required (...)+ loop did not match anything at input 'r'
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:15 mismatched tree node: n expecting <UP>
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:11 required (...)+ loop did not match anything at input 'r'
org\antlr\v4\parse\GrammarTreeVisitor.g: node from line 24:15 mismatched tree node: n expecting <UP>
error(20):  internal error: Rule LETTER undefined 
error(20):  internal error: element list has first|last == null 
Exception in thread "main" java.lang.NullPointerException
    at org.antlr.v4.automata.ParserATNFactory.elemList(ParserATNFactory.java:445)
    at org.antlr.v4.automata.ParserATNFactory.alt(ParserATNFactory.java:414)
    at org.antlr.v4.parse.ATNBuilder.alternative(ATNBuilder.java:567)
    at org.antlr.v4.parse.ATNBuilder.block(ATNBuilder.java:400)
    at org.antlr.v4.parse.ATNBuilder.subrule(ATNBuilder.java:1185)
    at org.antlr.v4.parse.ATNBuilder.element(ATNBuilder.java:887)
    at org.antlr.v4.parse.ATNBuilder.alternative(ATNBuilder.java:550)
    at org.antlr.v4.parse.ATNBuilder.ruleBlock(ATNBuilder.java:289)
    at org.antlr.v4.automata.ParserATNFactory._createATN(ParserATNFactory.java:148)
    at org.antlr.v4.automata.LexerATNFactory.createATN(LexerATNFactory.java:94)
    at org.antlr.v4.Tool.processNonCombinedGrammar(Tool.java:407)
    at org.antlr.v4.Tool.process(Tool.java:376)
    at org.antlr.v4.Tool.processGrammarsOnCommandLine(Tool.java:343)
    at org.antlr.v4.Tool.main(Tool.java:190)

So, what's the problem with my grammar ?

(Notice that this post can be a step further the one I exposed in this post, where I had a syntax error).

Was it helpful?

Solution

A couple of things are going wrong:

tag:        '['TAG_TYPE "TAG_VALUE"']';

Why are there double quotes around TAG_VALUE? Remove the quotes if you want to match the token TAG_VALUE: tag: '['TAG_TYPE TAG_VALUE ']';

MOVE_NUMBER\. MOVE_DESC MOVE_DESC

If you want to match the literal . (DOT) you need to put quotes around it (and not escape it!): MOVE_NUMBER '.' MOVE_DESC MOVE_DESC

NEWLINE:    \r? \n;

Again, if you want to match the literals, put quotes around it: NEWLINE: '\r'? '\n';

TAG_VALUE: .*;  
...
MOVE_DESC: .*;

Those rule will gobble up your entire input stream. You need another way to match a tag value and move description than you do now. Do not use .*.

EDIT

Here’s an existing PGN grammar: https://github.com/antlr/grammars-v4/tree/master/pgn

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