Installation

composer require iamsaint/yml

After that, make sure your application autoloads Composer classes by including
vendor/autoload.php.

How to use it

use iamsaint\yml\Writer;
use iamsaint\yml\components\{
    Shop,
    Currency,
    Category
}
// create shop
$shop = new Shop();
$shop->setName('Shop Name')
    ->setUrl('http://...')
    ->setCompany('My Company');
// create currency
$currency = new Currency();
$currency
    ->setId(Currency::RUR)
    ->setRate(Currency::DEFAULT_RATE);
// add currency
$shop->addCurrency($currency);
// create category
$category = new Category();
$category
    ->setId(1)
    ->setName("My category");
// create subcategory
$subCategory = new Category();
$subCategory
    ->setId(2)
    ->setParentId(1)
    ->setName("My subcategory");
// add categories to shop
$shop->addCategory($category);
$shop->addCategory($subCategory);
// create offer
$offer = new Offer();
$offer->setId(123)
    ->setUrl('http://...')
    ->setPrice(1000)
    ->setCurrencyId(Currency::RUR);
// add offer to shop    
$shop->addOffer($offer);
// create writer
$writer = new Writer();
// write to file
$writer->write('path/to/file.yml', $shop);