Facebook uses Hack. Hack is to PHP what C++ is to C, sort of. You can take PHP code and run it as Hack code, sometimes, but there are lots of reasons why PHP co

Facebook uses Hack. Hack is to PHP what C++ is to C, sort of. You can take PHP code and run it as Hack code, sometimes, but there are lots of reasons why PHP code might not be valid Hack code these days (Hack has diverged from upstream). https://en.wikipedia.org/wiki/Hack_(programming_language) https://en.wikipedia.org/wiki/Hack_(programming_language)