The official Hack Language specification.
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Hack Language Specification

This repo contains the Hack Language Specification. The easiest way to navigate the specification is via the table of contents.

The latest official release of the specification is 1.1.

You can run the specification tests with HHVM via its test runner and the Hack typechecker via hh_client.

Pull requests, issue filings and comments are extremely welcome.

Make sure you understand the contribution process.