Examples

Three complete, runnable apps, each building on the last. They live in the eventium-hs/examples repository.

Example	Store	Concepts
Counter CLI	in-memory	events, projection, command handler — the four primitives, ~100 lines
Café	SQLite	single aggregate with a real lifecycle, typed errors, a polling read model across processes
Bank	SQLite	full CQRS — multiple aggregates, a process manager with compensation, dual read models, event publishing

A natural progression: start with Counter for the core primitives, move to Café for persistence and subscriptions, then Bank for multi-aggregate CQRS.

Running them

The examples use Nix (with flakes) and direnv. Entering the directory auto-loads the dev shell via .envrc (which runs hpack to generate the .cabal files), so you get a fully pinned toolchain with no global installs.

git clone https://github.com/eventium-hs/examples
cd examples          # direnv loads the dev shell

cabal run counter-cli   # the counter REPL

Common just targets in the repo:

just build-local   # build against a sibling checkout of the library
just test          # run the test suites
just format        # ormolu
just lint          # hlint

The repo ships two project files: cabal.project.dev builds against a local ../eventium checkout (the day-to-day workflow), and cabal.project is the self-contained git-based build.

Reading them alongside the docs

Each walkthrough links back to the concept it demonstrates, so you can read the guide and the code side by side:

Counter → Projections, Command Handlers
Café → Read Models
Bank → Process Managers, Design & Internals