gistfile1.txt

trait Go[-I,O] { def go(i:I): O }

object Go {

  def go[A, B](f: A => B) = new Go[A, B] {
    def go(a: A) = f(a)
  }

  trait WhatMap[A, B] {
    def whatMap[A1](f: A1 => A): Go[A1, B]
  }

  implicit def toWhatMap[A, B](outer: Go[A, B]): WhatMap[A, B] =
    new WhatMap[A, B] {
      def whatMap[A1](f: (A1) => A): Go[A1, B] = new Go[A1, B] {
        def go(a1: A1): B = outer go f(a1)
      }
    }

  val g1 = go[String, Int](_.length)
  val g2 = g1.whatMap { cs: List[Char] => cs.mkString }

}