Introduction

This specification is intended to provide a complete and concise definition of the syntax and semantics of the Hack language, suitable for use by the following:

• Developers of a Hack implementation
• Implementers of a test suite for the Hack language
• Programmers writing Hack code

For now, the runtime library has been excluded, as that is documented at www.php.net and docs.hhvm.com. As such, all forward references to library facilities have placeholders of the form (§xx).