code: ExprList exprList() {
  		List<Expr> exprList = new ArrayList<Expr>();
  		while (true) {
  			Expr stat = expr();
  			if (stat != null) {
  				exprList.add(stat);
  				if (peek().sym == Sym.COMMA) {
  					move();
  					if (peek() == EOF) {
  						throw new ParseException("Expression error: can not match the char of comma ','", location);
  					}
  					continue ;
  				}
  			}
  			break ;
  		}
  		return new ExprList(exprList);
  	}
docs: exprList : expr (',' expr)*