We discuss history and evolution of string builders in Haskell, how linear types help us to tackle shared mutable state, what lessons can be learned from Java and how reading decade-old code can speed up things tenfold.

Since 2019, the International Software Architecture Qualification board has featured a three-day curriculum for Functional Software Architecture ("FUNAR") as part of its Advanced Level certification. We have taught more than 30 trainings based on this curriculum, mostly to audiences with little or no prior exposure to functional programming. In the training, we work through examples written in Haskell, among them a complete web application. The short duration of the course (which is usually preceded by a one-day introduction to functional programming) puts significant constraints on how much and what it can cover, but also poses didactic challenges as all material must be explainable and carry over to other functional languages. Over the past six years, we have continually assessed the effectiveness of the course and made many iterative improvements. We'll report on our experience and draw some inferences not just about teaching but also about viable software architecture in Haskell and what its advantages and differences are with traditional software architecture.

The next step forward in best-in-class tooling for Haskell is a modern step-through debugger. The promise is clear, be it for beginners interactively exploring the execution of a Haskell program, or experts grappling with a challenging bug in a multi-million LOC codebase.

We will introduce modern debugging in Haskell by example and highlight the features and robustness of the tool on various projects. We aim to convince users that the debugger is effortless to reach for and will become an essential of the future Haskell developer toolbox.

Hindsight is a typesafe, battery-included event-sourcing library for Haskell that makes event-sourced applications easy to write without sacrificing type-safety or performance.

It currently offers three event store backends (in-memory, filesystem, PostgreSQL) with a clean, unified API. The type system ensures you always work with the latest event versions, automatically upcasts old events through migrations, and helps generate golden tests to prevent breaking changes.

Features include real-time subscriptions (transient and catchup), asynchronous SQL projections for all stores, synchronous projections for PostgreSQL, and multi-stream transactions with version expectations à la EventStoreDB/KurrentDB.

Hindsight is extensively tested for correctness and is benchmarked to maintain competitive performance under realistic business loads.

"Programmable CAD" is a category of software where objects are defined using code. This talk covers how I’ve used programable CAD to design parts for 3D printing, why I think Functional Languages are uniquely suited for programable CAD, why I decided to write a programable CAD framework, and how the Scala Logo lead me to decorate a Christmas tree.