pairHeadingsParagraphs.scala

pairHeadingsParagraphs.scala

def packer[A](l: List[A])(f: A => Boolean): List[(A, List[A])] = {
  if ( l.isEmpty ) List()
  else if ( !f(l.head) ) List()
  else {
    val heading :: rest = l
    val (paragraphs, nextBunch) = rest span (false == f(_))
    (heading, paragraphs) :: packer(nextBunch)(f)
  }
}
case class Heading(title: String)
case class Paragraph(text: String)
type PS = Product with Serializable
type HP = List[(PS, List[PS])]
val haveOutput: HP = packer(List(
  Heading("Hello!"),
  Paragraph("hey"),
  Heading("Bang"),
  Heading("Tr"),
  Paragraph("OK"),
  Paragraph("OK")
))(_.isInstanceOf[Heading])


val expectedOutput: HP = List(
  (Heading("Hello!"), List(Paragraph("hey"))),
  (Heading("Bang"), Nil),
  (Heading("Tr"), List(Paragraph("OK"), Paragraph("OK")))
)


assert(haveOutput.toString == expectedOutput.toString, "Should match.")