How Functional is Direct-Style? (The Scala Workshop 2025)

Mon 13 - Tue 14 October 2025 Singapore

co-located with ICFP/SPLASH 2025

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The Scala Workshop 2025

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When

Mon 13 Oct 2025 14:00 - 14:20 at Peony West - Noon Chair(s): Oliver Bračevac, Hamza Remmal

Abstract

Direct-style is a recent trend in Scala, with several libraries being developed to support this approach. It’s also the style embraced by OCaml’s Eio and for writing effectful Unison programs.

Is direct-style still functional? Or is it just imperative programming, as some critics argue? Can functional and imperative styles coexist?

We’ll investigate what functional programming is at its core, how it relates to effects and properties such as referential transparency, immutability, idempotence and purity.

File attachments

Paper (direct_fp icfp.pdf)	17.51MiB

Bio

I am one of the co-founders of SoftwareMill, where I primarily code using Java, Scala, and other interesting technologies. I am actively involved in open-source projects, such as Ox, Tapir, sttp, Quicklens, ElasticMQ, and others. I have also been a speaker at major conferences, including JavaOne, Devoxx, GeeCON and ScalaDays.

In addition to writing closed- and open-source software, I spend my free time exploring various (functional) programming-related subjects. Any ideas or insights I gain usually end up with a blog (https://warski.org/articles).