executed and the following output is sent to the browser: Hello, World! Unlike PHP, Hack and HTML code do not mix; either XHP or another template engine needs to be used. Functions Like PHP 7, Hack allows types to be specified for function arguments and function return values. Functions in Hack are thus annotated with types like the following: // Hack functions are annotated with types. function negate(bool $x): bool { return !$x; } See also Parrot virtual machine Phalanger External links and Facebook Q&A: Hack brings static typing to PHP world A tutorial on converting an existing PHP project to Hack KPHP: An Executable Formal Semantics for PHP 2014 software Dynamically typed programming languages Facebook PHP software Programming languages compiled to bytecode Programming languages created in 2014 Scripting languages Statically typed programming languages