He is the technical lead on Hack, a programming language for HHVM that interoperates seamlessly with PHP. Prior to joining Facebook in 2011, Julien was a senior software engineer at Mylife.com, where he maintained and built the search engine for the site. Before that he was a software engineer at Esterel Technologies where he was instrumental in the development of the Scade 6 design verifier. He has a Masters in computer science from the Université Pierre et Marie Curie (Paris VI).