While working on the paper „Evolution of Functional UI Paradigms“, published at the FUNARCH workshop of ICFP 2025, I had a thought about pure functions that I would like to briefly explain here. As an argument in favor of pure functions, functional programmers often cite better testability: pure functions require no complicated test setup or mocks, are deterministic, parallelizable, etc. In tendency, this is certainly correct. Pure functions are often better suited for testing than their impure counterparts. However, this connection is not a neccessary implication in either direction: There are pure functions that are hard to test, and there are impure functions that are easy to test. Thus purity itself cannot be the substance that ensures a piece of program is properly testable. But then what is this substance?

Read on...

On March 13, 2026, BOB, Active Group‘s conference about the best in software development, will take place — once again in Berlin and once again at the Scandic Berlin Potsdamer Platz.

The Call for Contributions is open. Send us your proposal for a talk or tutorial (by November 17, 2025) — the program committee is looking forward to it!

Read on...

The Spring Framework and especially Spring Boot, are very popular and widely used for programming applications in Java. For Scala, there are other popular frameworks, particularly for programming web servers, such as the Play Framework.

In this small series of articles, we want to explore whether and to what extent we can program functionally in Scala while still using Spring Boot.

Read on...

This is an English translation of the German version of this post.

Read on...

Software must be configurable to be flexible. A configuration defines parameters and settings for software. Usually, the settings are stored in a configuration file that the software reads. But how do we ensure that a configuration is complete and valid? That all aspects that need to be configured are actually configured? That there are sensible defaults for values not explicitly configured? And that the values entered in the configuration are actually sensible values?

To avoid answering these questions anew for each project, we have developed a library for configurations for Clojure and ClojureScript that we have been using successfully for many years - and present in this article.

Read on...