antlr grammar to support google partial data api

Gdl.g

grammar Gdl;

options{
output=AST;
}

start : fieldlist;
fieldlist : field (COMMA field)* -> field*;
field : STRING L fieldlist R -> ^(STRING fieldlist)
    | STRING ;

STRING : ('a'..'z' | 'A'..'Z')+;
COMMA : ',' ; 
L   :   '(';
R   :   ')';