simpleMonad.scala

case class Hello {
	def hello = "hello"
}

case class Hi {
	def hi = "hi"
}

trait Greeting[C] {
	def greet(c: C): String
}

case class GreetingCaller[C : Greeting](g: C) {
	def greet = implicitly[Greeting[C]].greet(g)
}
object GreetingCaller {
  implicit def greeting2greetingCaller[C : Greeting](g: C) = GreetingCaller[C](g)
}

implicit object HelloGreeting extends Greeting[Hello] {
  def greet(h: Hello) = h.hello
}

implicit object HiGreeting extends Greeting[Hi] {
  def greet(h: Hi) = h.hi
}

import GreetingCaller._

def greetAll[G : Greeting](g: G) = println(g.greet)


greetAll(Hello())
greetAll(Hi())




case class FakeHi {
  def hi = "hi"
}

greetAll(FakeHi()) //error