xemantic-state

Small kotlin library for transforming state beans into reactive event streams. Even though small, it has multitude of use cases in my projects.

Use cases

Reacting to state mutations

In UI interfaces

flowPanel {
  button("Dock") {
    actionEvents.subscribe {
      state.robotMode = RobotMode.DOCKING
    }
    events.robotMode.subscribe { mode ->
      isEnabled = mode == RobotMode.FREE
    }
  }
}

See xemantic-kotlin-swing-dsl project for more details

In robotics

Collected sensor data is often a static state transmitted through the serial interface and obtained in a busy loop. But with xemantic-state it can be easily upgraded to reactive event streams delivering changes as they happen and triggering responses. It allows to avoid complexity and conditional execution paths. Also certain classes of problems are easier to solve - especially feedback loop based reactions. It's much easier to model certain aspects of cybernetic system with Functional Reactive Programming in mind.

events.robotMode
    .filter { mode -> mode == RobotMode.DOCKING }
    .doOnNext {
      logger.info { "Docking" }
      roomba.seekDock()
    }
    .flatMapMaybe {
      Observables.combineLatest(events.oiMode, events.current)
          .filter { pair ->
            (pair.first == OiMode.PASSIVE) && (pair.second > 0)
          }
          .firstElement()
    }
    .subscribe {
      state.robotMode = RobotMode.DOCKED
      logger.info { "Docked" }
    }

Once robot mode changes to DOCKING, command the Roomba robotic vacuum cleaner to seek the dock for charging. Roomba is not informing if the actual docking happens, therefore we wait until both - OI mode is switching to PASSIVE and the electric current is positive.

Imagine trying to model this as conditions in the busy loop continuously reading robot state.

2-way synchronization of state objects

distributed state

transparent use of OSC protocol

remoting of MIDI control

TODO

Some things are still missing:

xemantic-state-generator module

An apt processor generating classes like:

class MyStateEvents(e: Events<TestStateEvents>) {
  val foo by e.events<Int>()
  val bar by e.events<String>()
}

for corresponding:

class MyState(s: State<TestState>) {
  var foo by s.mutableProperty(42)
  var bar by s.mutableProperty("baz")
}

validation

Classes passed to the Keeper instance, even if generated, should be verified for correctness.

xemantic/xemantic-state