Swift Functional Programming - Second Edition

map, filter, and reduce

You may have wondered if we are going to be able to apply higher-order functions such as map, filter, and reduce to our linked list. We have implemented our linked list with a recursive enum and the recursive pattern is well suited to higher-order functions.

Let's start with map:

func map<T>(_ transform: (Element) -> T) -> LinkedList<T> {     switch self {     case .end:         return .end     case .node(let data, let next):         return transform(data) <| next.map(transform)     } } 

Using this method, we will be able to transform elements in our linked list. Nothing fancy here; we use the same cons operator that we defined before. The following statement will test our method:

 let mappedFunctionalLL = functionalLinkedList.map { $0 * 2 ...