# 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

```haskell
-- 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

```haskell
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

```yaml
dependencies:
  - eventium-core
  - eventium-memory
```

## Documentation

- [Main README](../README.md)
- [Design](../DESIGN.md)
- [Examples](../examples/)

## License

MIT -- see [LICENSE.md](LICENSE.md)