On the SitePoint PHP blog today Victor Berchet introduces HACK, the "replacement" for PHP inside the HHVM (HipHop Virtual Machine) from Facebook's development group. This is part two in the HACK/HHVM series.
HACK is an evolution of the PHP language designed to be safer, to enable better performance and to improve developer efficiency. Note that both HACK and PHP are equally supported by the HHVM. Despite the fact that HACK is in use at Facebook on all the production servers, only little info has leaked for now. In a nutshell, HACK is Facebook's PHP6 - it proposes to fix most of what's wrong with PHP today, while adding some new features like static typing along the way.
He starts with a look at typing and the static typing HACK uses instead of the dynamic typing of the normal PHP language. He mentions the "gradual typing" functionality, strict mode and the use of annotations. He also talks about XHP, the PHP extension that allows XML fragments to be translated into valid PHP (example included). He finishes off the post looking at a few other topics including asynchronous code execution, FastCGI support and the integrated debugger.