Isn't Hack basically compiled PHP so that it is faster for FB's use case? I understand it's not technically PHP, but I imagine it is effectively still PHP, or is it more like what C++ is to C?
I understand PHP is fast adding any actual language features that Hack has over it?
Slack migrated to Hacklang in 2016 [1].
[1] https://slack.engineering/hakana-taking-hack-seriously/ "We started migrating to a different language called Hack in 2016."