A simple type-safe formatter in Scala based on the "Functional Unparsing" paper by Olivier Danvy

Functional Unparsing.scala

// A simple type-safe formatter in Scala based on the "Functional Unparsing" paper by Olivier Danvy

// http://cs.au.dk/~danvy/DSc/16_danvy_jfp-1998.pdf

object Test {

  def eol[A](k: String => A)(s: String): A = {
    k(s + "\n")
  }

  def lit[A](x: String)(k: String => A)(s: String): A = {
    k(s + x)
  }

  def int[A](k: String => A)(s: String)(x: Int): A = {
    k(s + x.toString)
  }

  def str[A](k: String => A)(s: String)(x: String): A = {
    k(s + x)
  }

  def format[A](p: (String => String) => (String) => A): A = {
    p(identity[String])("")
  }

  def main(args: Array[String]): Unit = {
    val p1: (String => String) => (String) => (Int) => String             = int _
    val p2: (String => String) => (String) => (Int) => Int => String      = int[Int => String] _ compose int[String] _
    val p3: (String => String) => (String) => (Int) => String             = int[String] _ compose eol[String] _
    val p4: (String => String) => (String) => (Int) => String             = int[String] _ compose lit[String](" is the answer.") _ compose eol[String] _
    val p5: (String => String) => (String) => (Int) => String => String   = int[String => String] _ compose str[String] _ compose eol[String] _

    print(format(p1)(1))
    print(format(p2)(2)(99))
    print(format(p3)(3))
    print(format(p4)(4))
    print(format(p5)(42)(" is the answer again."))

  }
}