Oliver Bračevac

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.

We're running the 2026 #Scala Survey! Let us know how you are using Scala, #AI with Scala, and give hints to the Scala teams (both at @VirtusLab and @EPFL) on where the focus in driving Scala forward could be. Thank you - your answers count :) virtuslab.typeform.com/ScalaSurvey2026

@tribbloid @adamwarski For people who have followed Scala capture checking: we renamed "cap" to "any" a while ago, based on user feedback. github.com/scala/scala3/p…

@tribbloid @adamwarski T1^ means T1^{any} (scope-specific top elem). You're widening to {any}. Most precise capture-set for c1 is {c1} itself. More details in CC docs, esp. "scoped capabilities" chapter: nightly.scala-lang.org/docs/reference… We update regularly & welcome PRs/feedback.

A 01:46 introduction to what kind of problems capture checking in #Scala solves. Pushing forward what type systems might do!

After a long freeze, the Scala 3 standard library is again open to contributions. The main place for contributing is now the Scala 3 repository. details and link to process document: scala-lang.org/blog/2026/02/0…

@tribbloid @tiarkrompf Haha oh well, this is where I have to plead the fifth ;)

@etaconversion I honestly don't know the latest of its development havn't heard from @tiarkrompf 's team for years

me: real Futamura projection has never been tried Flavio: hold my parrot

@tribbloid Ackchyually, it does lots more than staging, it's a "compiler framework" which generates a graph-ir and aggressively optimizes it. It supports custom domain-specific optimizations, too. Anyway, its creator has been using Futamura's proj. to death RE: "never been tried"

@etaconversion about 20 yrs ago :D then it loses to Scala3 staging

Coffee’s good, but living rent-free in someone’s head? Delicious.

Congratulations @odersky for receiving the SIGPLAN Programming Languages Achievement Award! Your work is a great inspiration for me :) Well deserved!

We are thrilled to release Velvet: a foundational multi-modal verifier for imperative programs in Lean. It unifies execution, testing, automated and interactive proofs; and is itself proven sound. 💻 github.com/verse-lab/loom 📄 verse-lab.github.io/papers/loom-pr… 🧵 Learn more below ↓

@scaladays And @scaladays I spoke! Slides (incl. presenter notes) can be found here: bracevac.org/talks/

Looking forward to speak @scaladays

Generally, you need to port your libraries to CC if you want to offer full support. There are control knobs for what gets retained in the result of a method: (1) what you consider tracking-worthy capabilities, (2) the use of classifiers, and (3) consuming capabilities when doing separation checking. It is interesting to explore how monadic libraries could benefit from CC, and we'll have a writeup on that at some point. Much of this remains cutting edge science. (1) I think one can often replace the type-level acrobatics for effect labels with just capture sets, and have capture-set indexed monads. (2) One could try to extend the system to offer guaranteed purity for your monad implementations. (3) As already explored by @__protected , capabilities can be used for monadic reflection: github.com/lampepfl/monad… and CC can make that safe. (4) Lots of unexplored territory here! I'm looking forward to what people will come up with.

I am also wondering about that. Given that Iterator, a lazy construct, captures everything that was used in functions passed to its combinators, I fear a lazy monad would do the same. Maybe with classifiers we could select only things that we care about? Maybe @etaconversion could chip in?

I used to be skeptical of whether Martin's Caprese project is going to be able to bring much value to Scala, given how polished and well-designed the language already is. After Scala Days talks from his team I am now quite convinced the direction taken makes a lot of sense. I think that the standard library, for example, will make a lot more sense with capture checker guarding the less safe parts. For example, it is now my hope that separation checking will be able to make iterators safe from invalid use, even when they are returned from collection methods silently (a link to blogpost with the description of this problem in the reply). What is quite surprising to me is to see that some people still think that Caprese is about building some kind of alternative to existing purely functional libs. It seems more and more obvious to me that the objectives of this research are about building type-level tools to build new, safer and performant solutions that are not forced to rely on immutability and monadic suspension to keep us from making mistakes in our implementations. The one bit that is the most promising to me is the separation checking functionality that will yield linear typing and thus, along with capture checking, allow true and actual resource and mutability type safety that cannot be provided by any existing solution. I'm not gonna lie, Scala Days talks made me a believer, even if only a little. It seems to me that we can have nice things. I also agree now with Nicholas Rinaudo, who wrote that it seems the LAMP team will be able to deliver this improvement in a way that won't break everything for everyone. Kudos to Martin and his team, I'm now officially hyped.

@scaladays @scala_workshop Associations made by one of the OOPSLA reviewers 🤣

FINALLY, we can reveal the latest advances in Capture Checking for Scala, to appear at OOPSLA'25! CC now scales quite nicely and non-invasively to the standard collections library! We also have talks around CC at @scaladays next week and the @scala_workshop in October.

@tribbloid There's a number of "him"s who contribute nothing and sow only discord and lies. Just because they don't get their way and are denied power.

@etaconversion I have a vague idea of who "him" is but also think he is a red herring :D Real threats can't be that loud, and there is no conflict of interests

thank you @etaconversion , will give it a burl github.com/scala/scala3/i…

Shoutout to @KagiHQ for their paid search! I've never had to look beyond the first half of the first page to find what I wanted.

@icfp_conference @splashcon Update! The Scala Workshop 2025 submission deadline is now July 18, AoE (11:59 PM UTC-12). More time to submit your talk proposals! Original: x.com/scala_workshop…