HTTP Module
Build HTTP servers and clients using λÆS effects and virtual threads, with Circe JSON integration. HTTP Server · HTTP Client · JSON with Circe
λÆS — Yet Another Effect System
Algebraic Effects for Scala 3 — modular, composable, and built on Virtual Threads.
What is λÆS?
Section titled “What is λÆS?”λÆS is an experimental effect system for Scala 3 inspired by Algebraic Effects. Using Scala 3 context parameters and context functions, it provides a way to define, compose, and handle effects in a modular manner — without monads or complex type class hierarchies.
Effects are first-class: they are tracked in function signatures, composed freely, and executed by handlers. λÆS uses deferred execution and Java 25 Virtual Threads for safe, efficient concurrency.
Learn λÆS in 8 Steps
Section titled “Learn λÆS in 8 Steps”Step 1Getting StartedStep 2Core ConceptsStep 3Basic EffectsStep 4Error HandlingStep 5ConcurrencyStep 6State & ResourcesStep 7Streams & ChannelsStep 8Building Applications
Modules
Section titled “Modules”Integrations
Connect λÆS with the broader Scala ecosystem. Cats Effect 3 interop and SLF4J logging support. Cats Effect · SLF4J Logging
Featured Talk
Section titled “Featured Talk”Watch the talk from Scalar 2025 introducing the main concepts behind λÆS:
Community
Section titled “Community” GitHub Source code, issues, and contributions.
Maven Central Latest release and version history.
Contributing Guidelines for contributing to λÆS.