Idea for a metrics API for scalding and summingbird.

gistfile1.scala

// basically the state monad on a Map[String, Long] where String is the name, long is the delta,
// and P is some platform specific type
trait Metric[P, T] {
  def map[U](fn: T => U): Metric[P, U]
  // monoid merge the metrics of the result with this:
  def flatMap[U](fn: T => Metric[P, U]): Metric[P, U]

  def increment(kv: (String, Long)): Metric[P, T] = for {
    t <- this
    _ <- Metric.increment(kv)
  } yield t
  
  def commit(implicit provider: MetricsProvider[P]): T
  
  def deltas: Map[String, Long]
}

object Metric {
  def pure[T](t: T): Metric[P, T]
  def increment(kv: (String, Long)): Metric[P, Nothing]
}