Shopping Cart use-case

ShoppingCart.scala

object ShoppingCart {

  /*
   * Data has been taken from http://www.freebase.com/view/book/book_edition
   */
  
  implicit val mergeableItem = new Mergeable[Book] {}

  case class Book(name: String, 
                  creditedTo: Option[String], 
                  publisher: Option[String], 
                  publicationYear: Option[Int], 
                  binding: Option[String])

  def main(args: Array[String]) {

    var shoppingCart = MergeableListMultiset()

    shoppingCart = shoppingCart + Book("Brave New Words: The Oxford Dictionary of Science Fiction", Some("Jeff Prucher"), Some("Oxford University Press"), Some(2007), Some("Hardcover"))
    shoppingCart = shoppingCart + Book("On Lisp", None, Some("Prentice Hall"), Some(1993), Some("Paperback"))
    shoppingCart = shoppingCart + Book("The Logic of Failure: Why Things Go Wrong and What We Can Do to Make Them Right", None, Some("Perseus Books Group"), Some(1996), Some("Paperback"))
    shoppingCart = shoppingCart + Book("The Immaculate Conception", None, Some("House of Anansi Press"), Some(2006), None)
    shoppingCart = shoppingCart + Book("Bluebeard", Some("Kurt Vonnegut, Jr."), Some("Delacorte Press"), Some(1987), Some("Hardcover"))
    shoppingCart = shoppingCart + Book("On Lisp", None, Some("Prentice Hall"), Some(1993), Some("Paperback"))

    
    println("Shopping cart contents")    
    println(shoppingCart.map( (a: Tuple2[Book, Int]) => {
      val (book, count) = a
      "item: , count: ".format(book.name, count)
    }))

  }

}