public function asNumber(Row $row, FlowContext $context, int|float|null $default = null) : int|float|null
    {
        $result = $this->eval($row, $context);

        if (\is_string($result)) {
            return $default;
        }

        return \is_numeric($result) ? $result : $default;
    }

data_frame()
    ->read(from_csv(__DIR__ . '/data/orders.csv'))
    ->withEntry('is_numeric', \Flow\ETL\DSL\ref('discount')->isNumeric())
    ->withEntry('is_string', \Flow\ETL\DSL\ref('discount')->isType(\Flow\Types\DSL\type_string()))
    ->select('discount', 'is_numeric', 'is_string')
    ->limit(10)
    ->collect()
    ->write(to_output(truncate: false))
    ->run();