Friday 28 June 2013

Python-Compatible Syntax for Mypy Is Almost Ready

This is just a quick update about what has been happening in the mypy project recently.

I have been working on the new Python-compatible syntax along with writing my dissertation during the last months. I've also done a lot of design and evaluation work related to potential new exciting mypy features. I won't go into details now, but these include much more powerful type inference, union types and better parametric polymorphism for string types.

The new syntax is currently mostly functional. I'm very happy with the initial results, and this now seems like the obvious way forward for mypy. The most important test was when I translated the entire mypy implementation to use the new syntax this Tuesday. I was able to do it in just a few hours using an automatic translator tool that I had written earlier, though there was quite a bit of manual clean-up work afterwards.

The code is available in the pythonsyntax branch for anybody who wants to play with it:

Note that installing mypy now uses the standard approach instead of the old funky approach of using a git repository to distribute a runnable implementation. Have a look at the updated README for more information.

There is not much documentation, though. The wiki contains a short introruction to the new syntax:

The details of the syntax may still change, and I have many ideas of making the new syntax even better. I'll write about these later.