Instead of throwing out years of legacy code, Facebook built a new branch of the language that originally underpinned TheFacebook.com. Here's the story behind a two-year labor of love.

First created in 1993 to enhance the webpage of programmer Rasmus Lerdorf, PHP didn’t originate as a new programming language and as such it developed organically.

And while PHP itself has anonymous functions, Facebook claims Hack requires less work than PHP on the part of the programmer to make them useful.