> Is Hack-strict, apart from type annotations, a proper subset of PHP? No, but it's close. Here's a fairly comprehensive list of missing language features: htt

> Is Hack-strict, apart from type annotations, a proper subset of PHP? No, but it's close. Here's a fairly comprehensive list of missing language features: http://docs.hhvm.com/manual/en/hack.unsupported.php http://docs.hhvm.com/manual/en/hack.unsupported.php Theres also the question of HHVM—the runtime at the core of Hack—and its current support for PHP (which indirectly affects Hack's own support for PHP features it intends to have). It's also close, but not quite, at feature parity with PHP's internal runtime: http://hhvm.com/blog/2813/we-are-the-98-5-and-the-16 http://hhvm.com/blog/2813/we-are-the-98-5-and-the-16