Facebook started out PHP; but they ship-of-theseus'ed it into Hack by replacing the standard library, the language, and the runtime engine, so now it's a totall

Facebook started out PHP; but they ship-of-theseus'ed it into Hack by replacing the standard library, the language, and the runtime engine, so now it's a totally different thing with only a few superficial similarities (FWIW IMO Hack is much better than PHP, I'm sad that it never gained traction...)