antlr - ANTLR3 Tree Grammar: loop did not match anything at input 'EOF' -

i trying create first antlr3 tree grammar, keep hitting same problem. output of parser is:

$ echo 'foo, bar' | ./run.sh  foo bar treegrammar.g: node line 0:0 required (...)+ loop did not match @ input  'eof' exception in thread "main" java.lang.nullpointerexception     @ driver.main(driver.java:29) 

the output shows stage-1 parser results in right tokens ('foo' , 'bar'). somehow stage-2 tree-parser refuses parse results stage-1. since code basic, must simple, dumb oversight @ part ;-)

here's simple test code:

grammar.g:

grammar grammar;  options {     output = ast; }  statement: word (','! word)* eof!;  word: id;  id: ('a'..'z'|'a'..'z')+;  ws: (' ' | '\t' | '\n' | '\r')+ { $channel = hidden; } ; 

treegrammar.g:

tree grammar treegrammar;  options {     tokenvocab = grammar;     astlabeltype = commontree;     output = template; }  statement: word+;  word: id; 

driver.java:

import java.io.*; import org.antlr.runtime.*; import org.antlr.runtime.tree.*; import org.antlr.stringtemplate.*;  public class driver {     public static void main(string[] args) throws exception {         filereader groupfiler = new filereader("template.stg" );         stringtemplategroup templates = new stringtemplategroup(groupfiler);         groupfiler.close();          antlrinputstream input = new antlrinputstream(system.in);         grammarlexer lexer = new grammarlexer(input);         commontokenstream tokens = new commontokenstream(lexer);         grammarparser parser = new grammarparser(tokens);         grammarparser.statement_return result = parser.statement();         commontree t = (commontree)result.gettree();          system.out.println(t.tostringtree());          commontreenodestream nodes = new commontreenodestream(t);         nodes.settokenstream(tokens);         treegrammar walker = new treegrammar(nodes);         walker.settemplatelib(templates);         walker.statement();         treegrammar.statement_return r2 = walker.statement();         stringtemplate output = (stringtemplate) r2.gettemplate();          system.out.println(output.tostring());     } } 

assuming stringtemplate groups formed, problem fatc walk ast twice:

    walker.statement();     treegrammar.statement_return r2 = walker.statement(); 

e.g., call walker.statement() twice. (first) error telling you:

treegrammar.g: node line 0:0 required (...)+ loop did not match @ input 'eof'

you consume input once walker.statement() resulting node stream @ end (eof), , call walker.statement() again , expects tow walk word+ again, yet there's eof left.