Adam Warski

Sharing elegant solutions to everyday problems | CTO @ SoftwareMill | #Scala / functional programmer #FP | Blogger | #OSS developer

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Last Notes

2025-10-13 03:10:15 UTC

If you're at #icfpsplash25, join the #Scala workshop which runs now - all of Monday - and Tuesday morning. Lots of interesting talks! I'll be speaking as well, hopefully adding something interesting to the lineup: How functional is direct-style? See you there!
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2025-09-03 09:55:41 UTC

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@nprofile…c92e Yes of course :)
There are ways to generate OpenAPI spec from akka routes (through annotations), and I think zio-http worked on their own approach, but I'm not sure where this stands.

2025-09-03 08:31:59 UTC

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This way we get compile-time verification that the HTTP API is properly implemented on the backend and used on the frontend, continually during development: providing the precious quick feedback loop.
Try Bootzooka today: https://github.com/softwaremill/bootzooka

2025-09-03 08:29:55 UTC

In Bootzooka - our direct-style #Scala service template - there's a single source of truth when it comes to HTTP endpoints: the code-first description in the backend.
From that, during development, an `openapi.yaml` file is generated, after reach successful backend compilation. This file, in turn, is being monitored by yarn and generates #TypeScript services, which can be called from react components.

2025-08-22 15:54:44 UTC

Post-#ScalaDays hike! Just an hour away from Lausanne :)
Speaking of Scala conferences… if anything inspired you at ScalaDays, maybe it would make a good talk for the Scalar Conference? The c4p is closer than you think ;)
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2025-08-14 15:06:53 UTC

It's probably a standard at academic conferences, but I'm (positively!) surprised by the quality and detail of feedback I received for my #Scala Workshop submission!
Now it's my turn to incorporate that feedback and hopefully improve the talk. We'll see in October how it turns out!
And what about stealing that approach: a peer-reviewed technical conference - would that make sense? Preparing slides/papers upfront is something that's uncommon - but maybe we could also get unprecedented quality?

2025-08-12 12:22:31 UTC

How do LLMs call tools? What's the role of MCP? Do LLMs know about MCPs? Who decides when to call which tool?
Read all about that - with diagrams - in "How #MCP and #LLM tool calls work"! Enjoy :)
https://virtuslab.com/blog/ai/how-mcp-llm-tool-calls-work/

2025-08-11 14:10:27 UTC

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I can only hope you'll enjoy using Tapir, and if you haven't tried it yet, visit https://adopt-tapir.softwaremill.com!

2025-08-11 14:10:21 UTC

It's my pleasure to welcome New Work (Xing) as a Tapir adopter!
https://tapir.softwaremill.com/en/latest/adopters.html

2025-07-28 14:23:35 UTC

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* the code *did* need some review, which requires you to know what you're talking about
* be wary when asking LLM to commit - you might end up with the LLM eagerly committing later on its own!

2025-07-28 14:23:31 UTC

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* we need to come up with a new workflow: what to do in those 5-minute windows when the LLM is "thinking"?
* writing down an implementation plan & ironing out the requirement details works great - before any code is written
* you still need to know the libraries/frameworks you are using. I'm fairly confident of the resulting Scala/Tapir code, not so much about the TS/React one (esp that there's a compiler error, despite which everything seems to work? ;) )

2025-07-28 14:23:24 UTC

Type-safe vibe-coding a CRUD app: https://www.youtube.com/watch?v=mJ2uYnGR3lI
Featuring: JVM on the backend (Virtual Threads, direct-style, Scala, Tapir), TS on the frontend (React), Cursor, Bootzooka template, Claude 4 Sonnet
Some take-aways:
* compiler feedback & Scala's MCP server help a lot - the LLM iterates using this information and frequently invokes tools
* development is much faster, but still takes time; of course take this in the context of rather low-brain requirements of a CRUD app

2025-07-17 09:57:12 UTC

How to best provide the documentation of a library to LLMs, so that an AI coding assistant / agent is fully informed during development?
I've gathered a couple of options, and did a PoC on one of the libraries that I maintain.
Here are the results:
https://virtuslab.com/blog/backend/providing-library-documentation/

2025-07-16 10:11:42 UTC

Ox, the safe direct-style streaming, concurrency and resiliency library for #Scala 3 on the JVM, is nearing a 1.0.0 release, with 1.0.0-RC1 now available!
Should be finalized just in time for ScalaDays - in a month! :)
Please test! Is anything missing? Or worse - broken?
https://ox.softwaremill.com/latest

2025-07-14 16:57:33 UTC

Might seem like a tiny #Scala Metals features, but it really makes a difference: the status bar tells you that the code in the module you're currently in won't compile (hence - no new highlighting), because there are errors in an upstream module.
Here, `core-test` won't compile because `core` has errors, but this of course generalises to multi-module projects with long dependency chains, not only tests.
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2025-07-14 09:08:14 UTC

Comparing #Java Streams & Jox Flows: similar APIs on the surface, so why bother with a yet another streaming library for Java?
One is pull-based, the other push-based; one excels at transforming collections, the other at managing async event flows & concurrency.
https://softwaremill.com/comparing-java-streams-with-jox-flows/

2025-06-25 14:44:51 UTC

The time has come even for JavaScript frameworks to mature; Bartek Butrym created a walk-through of a modern @reactjs , @nextjs-based application architecture, everything from the folder structure, through tooling (linters), to validating forms!
https://softwaremill.com/modern-full-stack-application-architecture-using-next-js-15/

2025-06-25 12:07:10 UTC

More MCP examples written using Chimp!
1. proxying to a service available via HTTP: https://github.com/softwaremill/chimp/blob/master/examples/src/main/scala/chimp/weatherMcp.scala
2. exposing multiple tools: https://github.com/softwaremill/chimp/blob/master/examples/src/main/scala/chimp/twoToolsMcp.scala
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2025-06-24 09:36:53 UTC

Is there some standard / adopted (as in: used by Cursor / Anthropic's Claude / coding agents) way to provide documentation for libraries?
My use-case: I've got a library which works best when using certain approach to concurrency, error handling etc. So an MCP which has access to the API won't suffice. It's the general usage guidelines, not specifics, that I'd like to include in the context.

2025-06-20 08:19:28 UTC

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@nprofile…3f2j 🙈 I re-read the email but nothing is written there about not sharing, and I assumed that's what is not forbidden, is allowed ;)

2025-06-18 16:12:40 UTC

So ... what IS functional programming?
The video of my talk @LambdaDays is up! :) https://www.youtube.com/watch?v=pnZSff01FYQ

2025-06-17 10:06:32 UTC

Jox (#Java) & Ox (#Scala) - virtual thread-based safe concurrency & streaming - updates:
* `selectWithin` which guarantees that no elements are received from channels on timeout
* more `Flow` operators: `split` & `splitOn`
Find out more:
https://jox.softwaremill.com/latest/
https://ox.softwaremill.com/latest/
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2025-06-13 17:27:07 UTC

Thank you Devoxx & LambdaDays! It's been very intense three days, with great hallway/functional/Java/AI tracks :) Hope to see you next year!
The slides for both "Virtual Threads, 2 years later" and "What is Functional Programming" are available on my website: https://warski.org/talks/
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2025-06-09 07:29:03 UTC

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Fun fact: most of Chimp's code is auto-generated using Cursor with the help of Scala Metals MCP server.
Tasks such as generating the MCP JSON-RCP model - basing on the Typescript schema, writing tests or "filling in" missing code given a non-compiling API sketch turn out to be a great fit of LLMs.

2025-06-09 07:28:51 UTC

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Chimp supports any Scala stack, as it generates Tapir endpoints, which can be used with any Tapir server interpreter (including ones using cats-effect, ZIO, Pekko, synchronous servers).
The input schema is automatically derived using the same mechanism as in Tapir.

2025-06-03 09:09:07 UTC

This Thursday: #Kafka meetup in #Warsaw - 3 talks, varied topics (RT data streaming, Kafka queues, Outbox pattern) - join us! :)
https://www.meetup.com/warsaw-kafka-meetup/events/307958037/

2025-06-02 10:10:39 UTC

What's new in Ox 0.6.0 (safe direct-style concurrency and resiliency for #Scala on the #JVM)?
Firstly, Ox no longer uses preview JVM features, specifically StructuredTaskScopes and ScopedValues. Stabilization of these seems quite far off, and Ox now works with any JVM 21+.
Secondly, the `retry` API has been improved with more flexible schedules. They are composable & testable, which amounts to inspecting the list of intervals at which the operation might be triggered.
https://github.com/softwaremill/ox
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2025-05-28 19:32:00 UTC

Latest Tapir supports direct-style streaming bodies, including server-sent events. Cannot get much simpler ;)
Full scala-cli runnable example: https://github.com/softwaremill/tapir/blob/master/examples/src/main/scala/sttp/tapir/examples/sse/sseNettySyncServer.scala
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2025-05-20 15:29:24 UTC

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How are they different?
In the JEP variant, an additional `scope.join()` call is needed, which is absent when using the Jox API.
On one hand, this forces structured concurrency usages using the JEP to have a fixed structure: fork - join - get results.
The Jox variant can have arbitrary structure (mixed, multiple forks & joins), which is more flexible; and also has one less opportunity for misuse (in the JEP, you might forget to call `scope.join()`).

2025-05-19 10:59:39 UTC

This Wednesday: #Scala talks & refreshments at the #Amsterdam Scala meetup. In the lineup: modern effectful programming & marrying virtual threads with reactive streams.
Sign up here: https://www.meetup.com/amsterdam-scala/events/306861994/ & hope to see you there :)

2025-05-12 19:42:50 UTC

Binary search train
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2025-05-12 09:45:31 UTC

Von Reactive Streams zu Virtual Threads: mein Artikel für JavaPRO, jetzt auch auf Deutsch verfügbar!
https://javapro.io/de/von-reactive-streams-zu-virtual-threads/

2025-04-24 09:53:31 UTC

Tour of Jox: finite & infinite #Java streaming using flows, with reactive streams compatibility, (blocking) I/O integration, and a high-level, “functional” API.
More: https://jox.softwaremill.com/latest/flows.html
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2025-04-22 07:08:22 UTC

Tour of Jox: Go-like (selectable), completable, performant channels for #Java
Find out more: https://jox.softwaremill.com/latest/channels.html
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2025-04-22 06:50:28 UTC

Hope to see you tonight @ 7pm in #Tokyo for "From Reactive Streams to Virtual Threads"! :)
You can register here: https://jjug.doorkeeper.jp/events/183492

2025-04-08 13:51:06 UTC

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But not only :) Find out more: https://softwaremill.com/sttp-client-4-scala-http-client-released/

2025-04-08 13:50:58 UTC

sttp client v4 - the #Scala HTTP client you always wanted - released!
Simpler types, shorter names, fewer type parameters, clearer error messages, better IDE integration - these are the driving factors of the new stable release.
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2025-04-07 13:36:58 UTC

Hey Scalar and Rustikon attendees - you should get a questionnaire in your inbox - if you could leave your feedback for the conference and the talks, both the team and the speakers will be very grateful.
Thanks! :)

2025-04-01 10:56:21 UTC

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Here are the details: https://softwaremill.com/join-us/mid-senior-scala-developer/

2025-04-01 10:56:15 UTC

#Scala developers - the best remote-only company is looking for you! :) Disclaimer: you *do* need to communicate in Polish.
We're also looking for senior #Java, #Rust and #TypeScript devs. So if you're into type-checked languages, SoftwareMill is the place for you :)

2025-03-21 08:08:54 UTC

We're all set for Scalar - and if you don't have a ticket yet, now's the last chance :) (it's quite affordable as well!)
Next Thursday & Friday come & join us to explore what's ahead for #Scala and Functional Programming in a pragmatic, everyday setting!
https://www.scalar-conf.com
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2025-03-14 11:15:36 UTC

Will #AI help generate code that can be formally verified for correctness?
Not necessarily: AI's skills go as far as what a human does well. And both our achievements in formal verification, and probably more importantly the training set, are very limited.

2025-03-13 13:54:27 UTC

The #JVM is fast ... except on startup. But this is changing! Michał Zyga made a summary of the current efforts, how much code has to be changed, and how much gain they bring.
https://softwaremill.com/how-to-improve-jvm-based-application-startup-time/
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2025-03-10 15:39:11 UTC

We stick to our tradition and we've got a great Scalar lineup this year :) Lots of different themes & topics - what's new in #Scala the language, direct-style, alternative platforms, build systems, tools & concurrency, cloud & automation, onboarding, music, FP, enterprise, community.
Sounds interesting? Getting a ticket is just a few clicks. See you in #Warsaw in 17 days! :)
https://www.scalar-conf.com

2025-02-26 12:49:01 UTC

My last #Scala meetup in #Berlin was in 2013, time to update that :)
Join me tonight for an evening with 3 talks! https://www.meetup.com/scala-in-the-city/events/304875624/

2025-02-24 15:09:10 UTC

If you're in or near #Hamburg, why not decompress after the elections and join a #Scala meetup tomorrow evening?
https://www.meetup.com/scala-in-the-city/events/304875605/

2025-02-19 13:13:27 UTC

Why @nprofile…qyhl, in the age of #AI?
1. Asking the right questions
2. We'll write the code, that AI cannot (yet?) generate for you