ListPatternMatching

ListPatternMatching.scala

  def listPatternMatching[T](someList: List[T]): String = {
    someList match {
    case Nil => s"empty list"
    case x :: Nil => s"list with only one element"
    case List(x) => s"list with only one element" 
    case x :: xs => s"a list with at least one element. $x is the head xs to the tail,"   // xs could be Nil or some other list.
    case 1 :: 2 :: cs => s"lists that starts with 1 and then 2"
    case (x, y) :: ps => s"a list where the head element is a pair"
    case _ => s"default case if none of the above matches"
  }

  val pairs: List[(Char, Int)] = ('a', 2) :: ('b', 3) :: Nil
  val chars: List[Char] = pairs map {
    case (ch, num) => ch
  }
    
  
 def aFilter[A](list: AList[A], f: A => Boolean): AList[A] = {
    def loop (l:AList[A],result:AList[A]) :AList[A] = l match {
      case Nil => reverse(result)
      case Cons(head, tail) if(!f(head)) => loop(tail,Cons(head,result))
      case Cons(head, tail) if(f(head)) =>{
//        println("Second " + l,result)
        loop(drop(l,1),result)
      }

    }
    loop(list,Nil)
  }