Researcher in CS, Scala 3 Compiler Lead @epfl, Serves on the Scala Core Team and SIP committee. Agonizes over Effects, Capabilities & Ownership.
Switzerland
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Oliver Bračevac retweeted
New Scala LTS is out! Read all about it in the recent blog post by Wojciech Mazur at scala-lang.org/news/3.9/. The blog post covers all the most recent features, a quick reminder of all the ones since the last LTS, and practical information about migrating.
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The authors of @flixlang have a nice paper surveying the need for exclusion in the wild on GitHub. (And yes, we can do all their examples).
dl.acm.org/doi/abs/10.1145/3…
For us, the concrete problem was getting more of Scala's stdlib capture-checked, especially control and concurrency. The larger goal is capability tracking across all of Scala. TACIT uses the same machinery to statically limit what AI agents can do:
github.com/lampepfl/tacit
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Few production languages track effects. Fewer can say "anything except this category".
A Future needs that: its callback may capture anything *but not* thread-local state.
Scala 3 now supports this with capability classifiers. Accepted at OOPSLA 2026 🎉
arxiv.org/abs/2607.24504
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Work by Nguyen Pham, moi, Yichen Xu, Yaoyu Zhao, and @odersky
It's readily available in the Scala 3 nightly, try it out with
scala -S 3.nightly -language:experimental.captureChecking
nightly.scala-lang.org/docs/…
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Oliver Bračevac retweeted
New blog post that describes the ideas behind our award-winning paper on securing AI agents: martinodersky.substack.com/p…
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Programming languages aren’t dead. The problems are changing.
As software starts acting on our behalf, "what is this code allowed to do?" becomes a language question. That's what motivated tracked capabilities and Scala’s capture checking.
nightly.scala-lang.org/docs/…
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Our TACIT paper received a Best Paper Award @CAISconf!
Don’t just trust agents to use tools safely: have them generate code, check it before it runs, and use Scala capture checking to track which capabilities it may use or retain.
Type-safe AI infrastructure FTW.
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Oliver Bračevac retweeted
How can we ensure critical safety properties of AI agents? Like, no API keys leaked, no prompt injection, no data loss? It's a hard question which will require fundamentally rethinking the way we build modular software. We have an answer in our paper "Tracking Capabilities for Safer Agents" arxiv.org/abs/2603.00991, which I will present at the CAIS conference caisconf.org/ next week.
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Sadly, I must say that Opus 4.7, as observed by many here, has become too annoying to work with. GPT 5.5 has become noticeably better, but it still not satisfying for hacking the compiler.
Claude Pro vs Codex Pro on Scala compiler:
Claude is extremely good at Scala 3 and synthesizes idiomatic code, understands capture checking very, very well!
Codex: less elegant code, requires more handholding, but still fairly competent.
It flips on pencil-and-paper math.
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Thought @TheOfficialACM had uniform publishing standards across venues. Nope. ACM CAIS camera-ready: rip out biblatex (which acmart officially supports??) + other packages which entails significant rework for no reason. SIGPLAN doesn't do this. All for an HTML view nobody wants.
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Oliver Bračevac retweeted
Just gave a my talk: "How Can We Trust Our Agents?" at Scalar conference. Slides: slideshare.net/slideshow/how…
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Good news: we'll wipe contributors.scala-lang.org and users.scala-lang.org clean and make it an LLM-only forum. We've already set up two agents that will argue for resp. against braceless syntax. Scala marches on!
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