Code from: "An introduction to typeclasses in Scala"

intro_typeclasses.sc

#!/usr/bin/env amm
// Snippet 1
@scala.annotation.implicitNotFound("No Showable[A] in scope for A = ${A}. Try importing or defining one.")
trait Showable[A] {
  def show(a: A): String
}

// Snippet 2
object Showable {
  def make[A](showFn: A => String): Showable[A] = new Showable[A] { override def show(a: A): String = showFn(a) }
}

final case class UserName(first: String, last: String)
implicit val defaultUserNameShowable = Showable.make[UserName](userName => s"${userName.first} ${userName.last}")

val janeName = UserName("Jane", "Doe")

// Snippet 3
defaultUserNameShowable.show(janeName) // "Jane Doe"

// Snippet 4
implicit class ShowSyntax[A](val a: A) extends AnyVal {
  def show(implicit showable: Showable[A]): String = showable.show(a) 
}
janeName.show

// Snippet 5
implicit val secretUserNameShowable =  Showable.make[UserName](_ => "<secret person>")
//janeName.show

// Snippet 6
//java.util.UUID.randomUUID().show
// > typeclasses.sc:32: No Showable[A] in scope for A = java.util.UUID. Try importing or defining one.

// Snippet 7
trait SafeSerializable[A] {
  def serialize(a: A): Array[Byte]
  def deserialize(bytes: Array[Byte]): A
}
trait Functor[F[_]] {
  def map[A, B](a: F[A], f: A => B): F[B]
}