MyWorkflow.php

use Workflow\ActivityStub;
use Workflow\Workflow;
use Workflow\WorkflowStub;

class MyWorkflow extends Workflow
{
    public function execute($activity)
    {
        $result = yield ActivityStub::make($activity);
        return $result;
    }
}

$workflow = WorkflowStub::make(MyWorkflow::class);
$workflow->start(MyActivity::class);