func add4Inside<F: Mappable>(_ fa: Kind<F, Int>) -> Kind<F, Int> {
    F.map(fa) { $0 + 4 }
}

func main() {
  let nums: [Int] = [1,2,3,4]
  let opt: Int? = 4
  let task: Task<Int, Error> = Task { 4 }
  let result: Result<Int, Error> = .success(10)


  add4Inside(ArrayK(nums)).fix().value //> [5,6,7,8]
  add4Inside(OptionalK(opt)).fix().value //> Optional(8)
  add4Inside(TaskK(task)).fix().value //> Task(8)
  add4Inside(ResultK(result)).fix().value //> Result.Success(14)
}