am6.scala

def messageHandler: Receive = {
  case Start =>
    1 to trainingConcurrency foreach (_ => tdl ! nextTrainingBatch)
    1 to validationConcurrency foreach (_ => vdl ! nextValidationBatch)

  case Forward(yHat, y) =>
    val l = loss(yHat, y)
    l.backward()
    wire.prev ! Backward(yHat.grad)
    trainingLoss += l.data.squeeze()
    numTrainingBatches += 1

  case Backward(_) =>
    tdl ! nextTrainingBatch

  case Validate(x, y) =>
    numValidationBatches += 1
    validationLoss += loss(x, y).data.squeeze()
    validationScore += evaluator(x, y)
    if (numValidationBatches < validationDataLoader.numBatches)
      vdl ! nextValidationBatch

  case Epoch("training", epoch, duration) =>
    // report scores and losses, and reset counters
    ...     
    1 to validationConcurrency foreach (_ => vdl ! nextValidationBatch)
}