Reader Monad

Reader.scala

case class Reader[C, A](g: C => A) {
  def apply(c: C) = g(c)

  def map[B](f: A => B): Reader[C, B] = {
    Reader{ c => f(g(c)) }
  }

  def flatMap[B](f: A => Reader[C, B]): Reader[C, B] = {
    Reader{ c => f(g(c))(c) }
  }
}