lookyman/Pratchett requires PHP 5.5 or higher.
The best way to install lookyman/Pratchett is using Composer:
composer require lookyman/pratchettRegister the extension in your config.neon like this:
extensions:
pratchett: lookyman\Pratchett\DI\PratchettExtensionHomepage https://lookyman.net and repository https://github.com/lookyman/pratchett.