it would be really nice if we could count different things, or name groups differently on each platform.

Something like:

```def job[P <: Platform[P]](source: P#Source[T], sink: P#Sink[V], counters: P#Counters): TailProducer[Unit] =
  source.map { t =>
    counters("mapStep").inc
    fn(t)
  }.write(sink)
```
And then I count configure each of the counters by name on each platform (and maybe not do anything at all on some).

Might be something to think of down the line (platform specific counters).