List Operation: Prepend and Append

Prepending and appending an element to a list:

1 :: List(2, 3) // List(1, 2, 3)
1 +: List(2, 3) // List(1, 2, 3)
List(2, 3) :+ 1
// not working: List(2, 3) :: 1

List Operation: Map

Passing anonymous functions (lambda expressions) to a higher-order function map, increasingly omitting details such as argument types and names:

List(11,21,32).map((x:Int) => x+1)
List(11,21,32).map(x => x+1)
List(11,21,31).map(_ + 1) // List(12,22,32)

List Operation: Filter

Variations of the filter implementation Functions on Lists: Slide 23:

If in body of case

def filter [X] (xs:List[X], f:X=>Boolean) : List[X] = xs match 
  case Nil            => Nil
  case y::ys => 
    if f(y) then y :: filter (ys, f)
    else filter (ys, f)

Explicit negated condition

def filter [X] (xs:List[X], f:X=>Boolean) : List[X] = xs match 
  case Nil            => Nil
  case y::ys if f (y) => y :: filter (ys, f)
  case _::ys if !f (y)=>      filter (ys, f)