trying to recollect type class teachings of Mark Harrah

TypeClasses.scala

trait Builder[M[_], N[_]] {
  type Apply[T] = M[N[T]]
}

implicit def optionIntListBuilder: Builder[List, Option]#Apply[Int] = List.empty[Option[Int]]

// make a list of option[T] 
def make[T](implicit p: Builder[List, Option]#Apply[T]): List[Option[T]] = p

make[Int] // List[Option[Int]]

make[String] // error: could not find implicit value for parameter p: List[Option[String]]