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

• Main README
• Design
• Examples

License

MIT -- see LICENSE.md