typeclass.scala

trait Parser[A, B] {
  def parse(in: A): B
}

object Parser {
  implicit val intToStringParser: Parser[Int, String] =
    (in: Int) => {
      in.toString
    }

  def apply[A, B](implicit parser: Parser[A, B]): Parser[A, B] = parser
}


// doesn't work
def parse[A, B](in: A): B = Parser[A, B].parse(in)
// works
def parse[A, B](in: A)(implicit parser: Parser[A, B]): B = Parser[A, B].parse(in)

parse[Int, String](10)