return nil, err
	}

	t, ok := timeVal.ToTimestamp()
	if !ok {
		return nil, errNonTimestampArg
	}

	return extract(strings.ToUpper(e.Timeword), t)
}

func errUnsupportedCast(fromType, toType string) error {
	return fmt.Errorf("Cannot cast from %v to %v", fromType, toType)
}

func errCastFailure(msg string) error {
	return fmt.Errorf("Error casting: %s", msg)
}