Fred Emmott has a new post to his site sharing some of his experience with creating a "greenfield" project in Hack, the language Facebook developed to work with its HHVM runtime for PHP.

Until late 2015, the Hack and HHVM documentation site was a fork of PHP's own documentation site. This had many shortcomings, and ultimately we decided that the best approach would be something custom. As most of the public Hack code at that point was toy examples, we decided to also make the site itself open, and start investigating the greenfield problems.

There are 3 basic approaches to 'library code' in Hack if there isn't already a Hack version:

• Use a PHP library, without typechecker support
• Use a PHP library, and add HHI files so that Hack understands it
• Write something new

The Hack/HHVM site uses a mix of all three, though mostly #2 and #3.

He talks some about using plain PHP libraries in Hack projects and how you won't get the full benefit of Hack's features without some of the type-checking enforced (sometimes required to get some libraries working). Following this he covers the integration of three projects/structures, changed a bit for supporting Hack: FastRoute, PHPUnit and the things based on the PSR-7 request/response structure. He wraps up the post talking about writing "something new" and things to consider to make its APIs more "Hack-like".