Usage in a nutshell

usage.php

<?php

$reducers = [
    'create' => [
        '1.0' => function (array $currentState, array $actionData): ?array {
            # Calculate new state in here.
            # Things you should never do inside a reducer:
            # - Mutate its arguments;
            # - Perform side effects like API calls and routing transitions;
            # - Call non-pure functions, e.g. $object->method();
            
            return $actionData;
        }
    ]
];
// pass reducers to store
$store = new Store($reducers);
// dispatch events
$currentState = $store->dispatch(new Event());
// hydrate the aggregate root
$shipment = Shipment::fromState($currentState);