Functor

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?

	init(_ v: A) {
		value = 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.value!)
			return Maybe<B>.just(b);
		} else {
			return Maybe<B>.none()
		}
	}
}

var value: (() ->  A)?

init(_ v: A) {
  value = { return v }
}

func fromJust() -> A {
  return self.value!()
}

...

let b: B = fn(a.fromJust())