..., SymbolEnum.RPAREN,
(_1, e, _3) => (AstNode)e);
or grammar in NLT format:
// scanning
/[A-Za-z_][A-Za-z_0-9]*/ -> IDENTIFIER, IdentifierSymbol.Create($text);
// parsing
program -> list:namespace_list
{ new Program(currCoords(), (Namespaces)list) };
you should be able to use it :-).
There is Example project included which serves as tutorial.