code: @Override
      public Node visitArithmeticUnary(SqlBaseParser.ArithmeticUnaryContext context)
      {
          Expression child = (Expression) visit(context.valueExpression());
  
          switch (context.operator.getType()) {
              case SqlBaseLexer.MINUS:
                  return ArithmeticUnaryExpression.negative(getLocation(context), child);
              case SqlBaseLexer.PLUS:
                  return ArithmeticUnaryExpression.positive(getLocation(context), child);
              default:
                  throw new UnsupportedOperationException("Unsupported sign: " + context.operator.getText());
          }
      }
docs: ************** value expressions **************