block4.scala

// Write Json. In this case the type parameters in the type class
// came at the method parameters level (contra variant position), calling for having
// a `Contramap`

trait EncodeJson[A] { self =>

  def toJson(a: A): Json
  
  def contramap(f: B => A): EncodeJson[B] = new EncodeJson[B] {
  
    def toJson(a: B): Json = self.toJson(f(b)) 
  
  }

} // Implies EncodeJson can have an instance of contravariant functor

`