Koka is a good example of a language having effect sets: in koka, it's called a row of effects, and is written as

    <exn, console, e>

where single letters denote generic params.

In the case of needing a correlation id, this is a great use case for effects! First we declare an effect type:

    effect correlation_id
      ctl id(): int

Then we set up a handler:

    with ctl id()
      resume(7)

    log("nice!")

Here we just use 7, but we could be incrementing a counter per request or something.

Then any functions that are called in this scope, when they call 'id', will receive 7:

    fun log(message: string): <console, correlation_id> () {
      println(id())
      println(message)
    }

Which, using the above handler, would print:

    7
    nice!

For example. Hope this helps!