Swift Functional Programming - Second Edition

Contains

To make this LinkedList a little more interesting, we will develop a contains method similar to the one that we developed for the BST:

static func contains(_ key: Element, list: LinkedList<Element>) -> Bool {      switch list {      case .end:          return false      case .node(let data, let next):          if key == data {              return true          } else {              return contains(key, list: next)          }      } } 

This method recursively checks for a specific element in LinkedList and returns true if it finds the element:

print(LinkedList.contains(1, list: functionalLinkedList)) 

The result of this expression is going to be true.