context-dependent-wio

wio.scala

// This is a very minimal example showcasing how we can levarage type members to capture fixed types without the need
// to introduce more type parameters


trait WorkflowContext {
 
  type State
  type Event
  
  // operation that transforms In into Out, while guaranteeing the output is a substate os State
  sealed trait WIO[Err, In, Out <: State]
  object WIO {
    
    // example variant where IO is guarded with an event, IO is not run during recovery.
    // event is guaranteed to be subtype of Event
    case class HandleIO[Err, In, Out <: State, Evt <: Event](runIO: In => IO[Evt], handleEvent: Evt => Either[Err, Out]) 
      extends WIO[Err, In, Out]
  }
  
}


object WithdrawalContext extends WorkflowContext {
  type Event = WithdrawalEvent
  type State = WithdrawalState
}

class WihdrawalWorkflow(service: WithdrawalService) {
 
  // output type is specific to WithdrawalContext
  // runing this workflow requires persistance for WithdrawalEvent
  // at any point of time, we can get a state of the workflow which will be of type WitdrawalState
  def workflow: WidrawalContext.WIO[Nothing, Unit, WithdrawalState.Complete] = 
    WIO.RunIO(
      _ => service.doSth().as(WithdrawalEvent.SthDone),
      sthDone => WiithdrawalState.Completed()
    )
                                      
  
}

Shouldnt WithdrawalContext extend WorkflowContext?

Yes! Thanks for spotting, let me fix that