Rank and file

object R2 {
  trait R2[A] {
    def f (a :A) :A
  }
  trait R2Gen {
    def gen[A] :R2[A]
  }

  def foo (gen :R2Gen) {
    val x = "one"
    val r2str = gen.gen[String]
    println("str " + r2str.f(x))

    val y = 1
    val r2int = gen.gen[Int]
    println("int " + r2int.f(y))
  }

  def main (args :Array[String]) {
    foo(new R2Gen {
      def gen[A] = new R2[A] {
        def f (a :A) = a
      }
    })
  }
}

Just to relieve my own shame:

object R2 {
  trait R2Gen {
    def gen[A] :A => A
  }

  def foo (gen :R2Gen) {
    val x = "one"
    val r2str = gen.gen[String]
    println("str " + r2str(x))

    val y = 1
    val r2int = gen.gen[Int]
    println("int " + r2int(y))
  }

  def main (args :Array[String]) {
    foo(new R2Gen {
      def gen[A] = (a :A) => a
    })
  }
}