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  1. abstract class Ordering
  2. case class Less() extends Ordering
  3. case class Equal() extends Ordering
  4. case class Greater() extends Ordering
  5.  
  6. abstract class Order[T] {
  7. 	def compare(x: T, y: T): Ordering
  8. }
  9.  
  10. object UsualOrder {
  11. 	implicit object Ord extends Order[Int] {
  12. 		def compare(x: Int, y: Int): Ordering =
  13. 			if (x < y) Less() else
  14. 			if (x == y) Equal() else
  15. 			Greater()
  16. 	}
  17. }
  18.  
  19. object ReverseOrder {
  20. 	implicit object Ord extends Order[Int] {
  21. 		def compare(x: Int, y: Int): Ordering =
  22. 			if (x > y) Less() else
  23. 			if (x == y) Equal() else
  24. 			Greater()
  25. 	}
  26. }
  27.  
  28. object OrderedList {
  29. 	def empty = List()
  30.  
  31. 	def insert[T](x: T, xs: List[T])(implicit o: Order[T]): List[T] =
  32. 		xs match {
  33. 			case Nil => List(x)
  34. 			case y :: ys =>
  35. 				o.compare(x, y) match {
  36. 					case Less() => x :: xs
  37. 					case Equal() => xs
  38. 					case Greater() => y :: insert(x, ys)
  39. 				}
  40. 		}
  41.  
  42. 	def merge[T](xs: List[T], ys: List[T])(implicit o: Order[T]): List[T] =
  43. 		(xs, ys) match {
  44. 			case (_, Nil) => xs
  45. 			case (Nil, _) => ys
  46. 			case (x :: xs1, y :: ys1) =>
  47. 				o.compare(x, y) match {
  48. 					case Less() => x :: merge(xs1, ys)
  49. 					case Equal() => x :: merge(xs1, ys1)
  50. 					case Greater() => y :: merge(xs, ys1)
  51. 				}
  52. 		}
  53. }
  54.  
  55. object Main extends App {
  56. 	import OrderedList._
  57.  
  58. 	val xs = {
  59. 		import UsualOrder._
  60. 		insert(3, insert(1, insert(2, empty)))
  61. 	}
  62.  
  63. 	import ReverseOrder._
  64. 	val ys = insert(10, insert(8, insert(12, empty)))
  65.  
  66. 	println(xs)
  67. 	println(ys)
  68. 	println(merge(xs, ys))
  69. }
Success #stdin #stdout 0.39s 382016KB
comments (?)
stdin 
Standard input is empty
stdout 
List(1, 2, 3)
List(12, 10, 8)
List(12, 10, 8, 1, 2, 3)
https://ideone.com/L0yYfC
language:
Scala (scala 2.12.8)
created:
12 years ago
visibility:
public

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