ANTLR no viable alternative at input '<EOF>'

I'm still on the learning path with ANTLR. I've built a grammar and for the most part it does what I expect, but I need it to be able to run silently (no output to stdout or stderr).

Grammar

grammar MyPredicate;

options 
{
    output=AST; 
} 

parse   :   expression EOF
    ;

expression 
    :   field WS? OPERATOR_BINARY WS? value
    ;

OPERATOR_BINARY
    :   '=' | '<' | '>' | '<=' | '>=' | '!=' | 'has'
    ;

value   :   VALUE_STRING
    |   VALUE_NUMERIC
    |   VALUE_BOOLEAN
    ;

VALUE_STRING
    :   '""'
    |   '"' (ESC_SEQ | ~('\\'|'"'))+ '"'
    ;

VALUE_NUMERIC
    :   ('0'..'9')+ ('.' ('0'..'9')+)?
    ;

VALUE_BOOLEAN 
    :   'true'
    |   'false'
    ;

field   :   FIELD_NAME
    ;

FIELD_NAME 
    :   ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*
    ;

ESC_SEQ
    :   '\\' ('b'|'t'|'n'|'f'|'r'|'\"'|'\''|'\\')
    ;

WS  :   (' ' | '\t' | '\r' | '\n') {skip();}
    ;

Java

import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;

public class Main {
    public static void main(String[] args) throws Exception {
        MyPredicateParser parser = new MyPredicateParser(new CommonTokenStream(new MyPredicateLexer(new ANTLRStri开发者_Python百科ngStream(args[0]))));
        MyPredicateParser.parse_return r = parser.parse();
        parser.parse();

        if ( r.tree!=null ) {
            System.out.println(((Tree)r.tree).toStringTree());
            ((CommonTree)r.tree).sanityCheckParentAndChildIndexes();
        }
    }
}

Input

a = 1

Output

line 0:-1 mismatched input '<EOF>' expecting FIELD_NAME
a = 1 null

I'm not sure why I get the EOF error. From what I understand my grammar is parsing correctly, and I get the error after the "parse" parser is evaluated, but that node is looking for the EOF. Using ANTLR 3.2

The problem is that you're calling parse() twice in your Main class. Remove the line:

parser.parse();

leaving only:

MyPredicateParser.parse_return r = parser.parse();

in place.