Explore Slack's journey of migrating from PHP to Facebook's Hack programming language in this 31-minute conference talk from the International PHP Conference. Discover the surprising, challenging, and beneficial aspects of transitioning a multi-million line PHP codebase. Learn about Hack's features, including static type checking, inferred generics, union types, and type-safe HTML with XHP. Gain insights into the differences between PHP and Hack arrays, type refinement, and the Hack Standard Library. Understand the process of eliminating PHP dependencies and the lessons learned during the migration. Draw inspiration for your own projects as the speaker reflects on the benefits and drawbacks of Hack, offering valuable perspectives for the PHP community.