phooji

Pyre is faster in some circumstances.

With that said, the real answer is 'it depends', and it may well be the case that mypy serves your needs better.

I think (2) is the overriding concern: we're getting really great results with the static analysis tools we've built internally on top of the Hack type checker. Building a similar tool on top of mypy would've required fairly invasive changes; we decided to use the Hack type checker infra instead.

Full disclosure: I worked on the Hack type checker briefly, a long time ago :)

Please send us a pull request if this is something you'd like this to live in the pyre-check repo!

You can run Pyre without using watchman if your editor-of-choice supports LSP -- the two modes are basically complementary. You can also run `pyre check` in non-incremental mode, though that may be slower depending on the size of your codebase.

Good question [I am the 'Pieter' on that blog post]. There will be a talk at PyCon that covers parts of this. It comes down to two reasons:

1) Performance. We needed something that would consistently work quickly on Instagram's server codebase (currently at several million lines).

2) We are building deeper semantic static analysis tools on top of Pyre. We've built some of these tools for Hack/PHP already, so following the Hack type checker's architecture is the best way for us to achieve this.