# Roundabout

*\<currently in an experimental state\>*

An message oriented concurrent runtime.

Roundabout uses a single message bus that is causal consistent for the whole program.
This bus is then read in parallel by message handlers that can modify their internal state and send messages.

## Cargo

To use roundabout in your project add the following to your `Cargo.toml`:

```toml
[dependencies]
roundabout = "0.2.0"
```

## Hello World
```rust
use roundabout::prelude::*;

#[derive(Debug)]
pub struct PingEvent(u64);

#[derive(Debug)]
pub struct PongEvent(u64);

#[derive(Default)]
pub struct PingState {
    count: u64,
}

fn ping_handler(builder: OpenMessageHandlerBuilder<PingState>) -> InitMessageHandlerBuilder<PingState> {
    builder
        .on::<PingEvent>(|state, context, ping| {
            println!("Ping: {:?}", ping);
            context.sender().send(PongEvent(state.count));
            state.count += 1;
        })
        .init_default()
}

#[derive(Default)]
pub struct PongState {
    count: u64,
}

fn pong_handler(builder: OpenMessageHandlerBuilder<PongState>) -> InitMessageHandlerBuilder<PongState> {
    builder
        .on::<PongEvent>(|state, context, pong| {
            println!("Pong: {:?}", pong);
            state.count += 1;
            context.sender().send(PingEvent(state.count));
        })
        .init_default()
}

fn main() {
    Runtime::builder(512)
        .add(ping_handler)
        .add(pong_handler)
        .finish()
        .start(PingEvent(0));
}

```

## Further steps

Take a look at the examples and benches.

## Licence

Roundabout is dual-licensed under Apache 2.0 and MIT.

See [LICENSE_APACHE](LICENSE_APACHE) and [LICENSE_MIT](LICENSE_MIT)