Every frame has a schema. printSchema() shows it, and a ? marks a nullable column.
Examples
Getting started
Description
Documentation
Every frame carries a schema, and it is available before the frame is executed.
Code
<?php
declare(strict_types=1);
use function Flow\ETL\DSL\{data_frame, from_array, int_schema, schema, str_schema};
require __DIR__ . '/vendor/autoload.php';
data_frame()
->read(from_array([
['id' => 1, 'name' => 'Norbert'],
['id' => 2, 'name' => 'Jane'],
], schema(int_schema('id'), str_schema('name'))))
->printSchema();