gistfile1.scala

object Formatter {
  sealed abstract class Dir[A] {
    def formatAux: String => A
    def format: A = formatAux.apply("")
  }

  case object E extends Dir[String] {
    def formatAux = identity
  }

  case class L[A](s: String, d: Dir[A]) extends Dir[A] {
    def formatAux =
      (out: String) => d.formatAux.apply(out + s)
  }

  case class I[A](d: Dir[A]) extends Dir[Int => A] {
    def formatAux =
      (out: String) =>
        (i: Int) =>
          d.formatAux.apply(out + i.toString)
  }

  case class S[A](d: Dir[A]) extends Dir[String => A] {
    def formatAux =
      (out: String) =>
        (s: String) =>
          d.formatAux.apply(out + s)
  }

  def test = {
    println(L("hello, ", S( L("!", (E)))).format("world"))
  }
}