Patternmatching.scala

Pm scala

def flatten(ls: List[_]): List[Int] = ls match {
    case Nil => Nil
    case (a: Int) :: tail => a :: flatten(tail)
    case (a: List[_]) :: tail => flatten(a) ::: flatten(tail)
    case _ :: tail => flatten(tail)
  }

// oppure adforittura

def flattenRecur(ls: List[Any]): List[Int] = ls match {
    case (head: Int) :: (tail: List[Any]) => head :: flattenRecur(tail)
    case (head: List[Int]) :: (tail: List[Any]) => head.head :: flattenRecur(head.tail :: tail)
    case (head: List[Any]) :: (tail: List[Any]) => flattenRecur(head) :: flattenRecur(tail) // non-variable type... on this line.
  }
  
  
  Opure in haskell
  
  
:: (Show a) => [a] -> String  
tell [] = "The list is empty"  
tell (x:[]) = "The list has one element: " ++ show x  
tell (x:y:[]) = "The list has two elements: " ++ show x ++ " and " ++ show y  
tell (x:y:_) = "This list is long. The first two elements are: " ++ show x ++ " and " ++ show y