“Hack is a programming language for HHVM that interoperates seamlessly with PHP,” reads the “Hack Lang” website. “Hack reconciles the fast development cycle of PHP with the discipline provided by static typing, while adding many features commonly found in other modern programming languages.”
The problem that Facebook addressed with Hack is the problem of the slower pace of static code typing and the lesser accuracy of dynamic typing. “At Facebook scale — with thousands of engineers shipping new code twice a day — slowdowns like these are even more problematic,” wrote Facebook’s Julien Verlaguet in an announcement. Hack is designed to be a sweet spot for both.
Facebook has tried to make it as easy as possible to migrate any existing code, and indeed you can add Hack incrementally to your existing PHP files. If you want to give Hack a spin, you can get cracking at Hacklang.org. There’s also a Hack development day you can attend on April 9th.