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post.scala

type PrettyPrint[ScalaValue] = String
  val interpretAsPrettyPrint = new Language[PrettyPrint] {
    override def number(v: Int): PrettyPrint[Int] = s"($v)"
    override def increment(a: PrettyPrint[Int]): PrettyPrint[Int] = s"(inc $a)"
    override def add(a: PrettyPrint[Int], b: PrettyPrint[Int]): PrettyPrint[Int] = s"(+ $a $b)"

    override def text(v: String): PrettyPrint[String] = s"[$v]"
    override def toUpper(a: PrettyPrint[String]): PrettyPrint[String] = s"(toUpper $a)"
    override def concat(a: PrettyPrint[String], b: PrettyPrint[String]): PrettyPrint[String] = s"(concat $a $b)"

    override def toString(v: PrettyPrint[Int]): PrettyPrint[String] = s"(toString $v)"
  }