From Wired, Facebook Introduces â€˜Hack,â€™ the Programming Language of the Future
You can think of Hack as a new version of PHP. It too runs on the Hip Hop Virtual Machine, but it lets coders use both dynamic typing and static typing. This is whatâ€™s called gradual typing, and until now, it has mostly been an academic exercise. Facebook, Oâ€™Sullivan says, is the first to bring gradual typing to a â€œreal, industrial strengthâ€ language.
Hack is open source and is available at hacklang.org. It supports type annotation, generics, lambdas and host of other features on top of PHP.