[antlr-interest] Wildcard in tree grammar? - was validating semantic predicates

[Harald M. Müller]

Sorry - I had the wrong output in my posting: The ignore version of course
outputs simply

    whoaa

as intended ...

Regards
Harald M.

------------------------------

Hi tree grammar gurus -

I wrote to mark about that "ignore rule" - but now I found on the Wiki page
http://www.antlr.org/wiki/display/ANTLR3/Simple+tree-based+interpeter that
"The wildcard says skip the entire subtree (new in 3.0b6)." 
However, the program below does NOT work (at least for me?) when I replace
the call to ignore with a simple wildcard (dot). Instead, it says 

   whoaa
   Tree.g: node from line 1:37 no viable alternative at input 'if'
   :-(

- whereas the "ignore" version simply outputs

   whoaa
   :-(

as intended.
Has anyone a clue why's that so?? (it seems to have to do something with the
lookahead on the tree node stream, doesn't it?)

Regards
Harald M.

P.S. Mark, there's your running example :-)

-----------------

grammar LexerParser;

options {
	language=CSharp;
	output=AST;
	ASTLabelType=CommonTree;
}

file
    : (statement ';'!)+
    ;

statement
    : simpleStatement
    | 'if'^ condition statement
    ;
    
simpleStatement
    : 'print'^ 'true'
    | 'print'^
    ;
    
condition
    : 'true'^
    | 'false'^
    ;

WS  :  (' '|'\r'|'\t'|'\f'|'\n')+ { $channel=HIDDEN; };

-----------------

tree grammar Tree;

options {
	language=CSharp;
	tokenVocab=LexerParser;
	ASTLabelType=CommonTree;
}

file
    : (statement)+
    ;

statement
    : simpleStatement
    |  
      ^('if' x=condition ( { x }? =statement
                         |           .           // instead of ignore - the
Wiki says: "The wildcard says skip the entire subtree (new in 3.0b6)."
                         )
       )
   ;
   
//ignore
////    : . (DOWN (ignore)* UP)?
//    : ^(. (ignore)*)
//    ;
    
simpleStatement
    : ^('print' 'true') { Console.Out.WriteLine("whoaa"); }
    | 'print' { Console.Out.WriteLine(":-("); }
    ;
    
condition returns [bool result]
    : 'true' { result = true; }
    | 'false' { result = false; }
    ;

------------------

using System;
using Antlr.Runtime;
using Antlr.Runtime.Tree;

class Program {
    static void Main() {
        ICharStream s = new ANTLRStringStream("if true if 
true print true; if false if true print;");

        LexerParserLexer l = new LexerParserLexer(s);
        CommonTokenStream ts = new CommonTokenStream(l);
        LexerParserParser parser = new LexerParserParser(ts);
        ITreeNodeStream tns = new 
CommonTreeNodeStream(parser.file().Tree);
        new Tree(tns).file();

        Console.In.Read();
    }
}