Haskell/Rust programmer. Views expressed are my own.
Cambridge/London, UK
Joined March 2010
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Today I spent 8 hours to change 2 lines of code (github.com/facebook/pyrefly/…). That involved:
* 30,342,810 line example that caused a crash
* 97 compilations
* 1.3Gb of log files
* 6 historic diffs
* 3 computers
* 2 whiteboards of notes
It's like a day long logic puzzle :)
Neil Mitchell (neildmitchell @🪡) retweeted
New-ish @galois blog: “What Works (and Doesn't) Selling Formal Methods”. The boring truth: engineers are rational and adoption is all about cost/benefit tradeoffs
Neil Mitchell (neildmitchell @🪡) retweeted
🚀New Project Alert🚀
We recently launched an open source project, Pyrefly. It's a new type checker and IDE experience for Python. Lightweight, accurate, and designed for scale, Pyrefly is an excellent fit for your Python workflow!
Learn more: engineering.fb.com/2025/05/1…
Pyrefly (our Python type checker) got a blog post (engineering.fb.com/2025/05/1…) and podcast (open.spotify.com/episode/4Jh…) today. Available from pyrefly.org if you want to give it a try.
Heading off to PyCon to talk about Pyrefly, the Python type checker I've been working on for the past 9 months. us.pycon.org/2025/schedule/p…
I'll be talking at this about Buck2
🎉 Build Meetup London - May 22 @ 11 AM! Expert insights on Bazel migration & scaling, Buck2, & build strategies. Plus, a hands-on unconference session.
Register: share.hsforms.com/2-kAtpya7S…
❤️ Hosted by EngFlow, @JaneStreetGroup, and @tweagio.
#Bazel #Buck2 #BuildSystems #DevOps
ALT London Build Meetup on 22 May 2025 at 11 AM. Hosted by Tweag, Jane Street, and EngFlow.
Neil Mitchell (neildmitchell @🪡) retweeted
Rust 1.85.0 has been released! 🌈🦀✨
Not only does this release add async closures, it also includes a whole new Rust Edition, Rust 2024! 🎆🚀
Check out the blog post for an overview of all the changes and additions: blog.rust-lang.org/2025/02/2…
HLint (Haskell linter) v3.10 out, which now works with GHC 9.8-9.12. A few little hints here and there too. hackage.haskell.org/package/…
Neil Mitchell (neildmitchell @🪡) retweeted
I don't recommend developing two build systems, and then switching from one to the other, but that's what we at Jane Street accidentally did. And what a journey it was!
In the end, we're finally using Dune to build all our 70M+ lines of OCaml & Python 🙌
blog.janestreet.com/how-we-a…
Neil Mitchell (neildmitchell @🪡) retweeted
This Linux-kernel-RCU bug fought well: people.kernel.org/8q9a9dt4q3
Very cool talk on building D binaries with Buck2 - youtube.com/live/AzezZhvIyS4… by Max Haughton
Neil Mitchell (neildmitchell @🪡) retweeted
I’ve done a lot of formal methods “technical sales” - trying to scope projects for Galois clients that solve their problem and fit into a budget. I gave a talk last week on some things that I learned along the way: mikedodds.github.io/files/ta…
Released the Haskell extra library 1.8, now with support for the upcoming GHC 9.12. Mostly a lot of handy list functions - hackage.haskell.org/package/…
My Haskell Uniplate library got ported to Rust - crates.io/crates/uniplate. Allows doing traversals by type, eg making it easy to work with big syntax trees. I've been using these ideas in Rust a while (eg github.com/facebook/starlark…) but happily someone made them a proper library!
Neil Mitchell (neildmitchell @🪡) retweeted
I finally wrote down my thoughts on the design of the LSP, both good and bad: michaelpj.com/blog/2024/09/0…
Got starlark-rust working with WASM/JS, so you can now run Starlark (approximately simplified Python) in your browser. Based on code from april.dev/. PR at github.com/facebook/starlark….
Haskell XML parsing library `hexml` (github.com/ndmitchell/hexml) gets an update after 6 years! Now supports <![CDATA[ ]]>, thanks to a contribution from mniip.com/. Hexml is a very fast XML parser written in C, designed for easy wrapping as a fast Haskell XML library.
My 11yo made a platformer scratch game - scratch.mit.edu/projects/100… - requires keyboard control. Finally a scratch game from him with a reasonable difficulty curve!