cf.scala

object Main {

  trait Executor {}

  trait Context {
    def data: String
  }

  type IO[T] = Executor ?=> T
  type Result[T] = Context ?=> IO[T]

  class Downstream {
    def fetch(): Result[String] = {
      val c = summon[Context]
      s"response ${c.data}"
    }
  }

  class Service {
    val downstream = new Downstream()
    def execute(): Result[String] = {
      val c = summon[Context]
      downstream.fetch()(using
        new Context {
          override def data: String = s"${c.data}-service"
        }
      )
    }
  }

  def main(args: Array[String]): Unit = {
    given e: Executor = new Executor {}
    given c: Context = new Context {
      def data: String = "entry-point"
    }
    val svc = Service()
    println(svc.execute())
  }

}