eventium-memory: In-memory implementations for eventium

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[tz-upper-bounds] On library, these packages have upper bounds with trailing zeros: - eventium-core Please avoid trailing zeros for upper bounds.

Eventium-memory provides in-memory implementations of event stores and projection caches for the Eventium event sourcing framework. This package is ideal for development, testing, and prototyping event-sourced applications without requiring external dependencies like databases. All data is stored in STM-based concurrent data structures for thread-safe access.

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Properties

Versions	0.1.0, 0.2.0, 0.2.1
Change log	CHANGELOG.md
Dependencies	base (>=4.9 && <5), containers (>=0.6 && <0.8), eventium-core (>=0.2.0 && <0.3.0), mtl (>=2.2 && <2.4), safe (>=0.3 && <0.4), stm (>=2.5 && <2.6) [details]
License	MIT
Author
Maintainer	Alexander Sidorenko
Category	Database, Eventsourcing
Home page	https://github.com/aleks-sidorenko/eventium#readme
Bug tracker	https://github.com/aleks-sidorenko/eventium/issues
Source repo	head: git clone https://github.com/aleks-sidorenko/eventium
Uploaded	by aleks_sidorenko at 2026-03-05T10:40:39Z

Modules

Eventium
- ProjectionCache
  - Eventium.ProjectionCache.Memory
- Store
  - Eventium.Store.Memory

Downloads

eventium-memory-0.2.0.tar.gz [browse] (Cabal source package)
Package description (as included in the package)

Maintainer's Corner

Package maintainers

aleks_sidorenko

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Readme for eventium-memory-0.2.0

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Eventium Memory

In-memory event store for Eventium, backed by STM.

Overview

eventium-memory provides thread-safe, in-memory implementations of EventStoreReader and EventStoreWriter for development, testing, and prototyping. No external database is required.

API

-- Create a TVar-backed store
eventMapTVar :: IO (TVar (EventMap event))

-- TVar-based (for use inside STM or lifted to IO)
tvarEventStoreReader       :: TVar (EventMap event) -> VersionedEventStoreReader STM event
tvarEventStoreWriter       :: TVar (EventMap event) -> VersionedEventStoreWriter STM event
tvarGlobalEventStoreReader :: TVar (EventMap event) -> GlobalEventStoreReader STM event

-- MonadState-based (for pure state threading)
stateEventStoreReader       :: (MonadState (EventMap event) m) => VersionedEventStoreReader m event
stateEventStoreWriter       :: (MonadState (EventMap event) m) => VersionedEventStoreWriter m event
stateGlobalEventStoreReader :: (MonadState (EventMap event) m) => GlobalEventStoreReader m event

Use runEventStoreReaderUsing atomically / runEventStoreWriterUsing atomically to lift the STM stores into IO.

Usage

import Control.Concurrent.STM (atomically)
import Eventium
import Eventium.Store.Memory

main :: IO ()
main = do
  tvar <- eventMapTVar
  let writer = runEventStoreWriterUsing atomically (tvarEventStoreWriter tvar)
      reader = runEventStoreReaderUsing atomically (tvarEventStoreReader tvar)

  result <- applyCommandHandler writer reader myHandler aggregateId cmd
  print result

When to Use

Testing -- fast, isolated, no I/O overhead.
Prototyping -- iterate on domain logic without database setup.
Examples -- the counter-cli example uses this backend.

For persistent storage, use eventium-sqlite or eventium-postgresql.

Installation

dependencies:
  - eventium-core
  - eventium-memory

Documentation

License

MIT -- see LICENSE.md