gistfile1.swift

class F<A> {
}

protocol Functor {
  typealias A
  typealias B
  typealias FA = F<A>
  typealias FB = F<B>
  func fmap(a: FA, fn: (A -> B)) -> FB
}

class Maybe<A: Any>: F<A> {
  var value: (() -> A)?
  
  func fromJust() -> A {
    return self.value!()
  }
  
  init(_ v: A) {
    value = { return v }
  }
  
  init() {}
  
  class func just(t: A) -> Maybe<A> {
    return Maybe(t)
  }
  
  class func none() -> Maybe {
    return Maybe()
  }
  
  func isJust() -> Bool {
    switch value {
    case .Some(_): return true
    case .None: return false
    }
  }
}

extension Maybe: Functor {
  typealias B = Any
  func fmap(a: Maybe<A>, fn: (A -> B)) -> Maybe<B> {
    if a.isJust() {
      let b: B = fn(a.fromJust())
      return Maybe<B>.just(b);
    } else {
      return Maybe<B>.none()
    }
  }
}