Result

Result.swift

func identity<T>(value: T) -> T {
    return value
}

enum Result<T, E> {
    case Success(T)
    case Error(E)
    
    func map<R>(f: (T) -> R) -> Result<R, E> {
        return mapResult(success: f, failure: identity)
    }
    
    func mapError<R>(f: (E) -> R) -> Result<T, R> {
        return mapResult(success: identity, failure: f)
    }
    
    func mapResult<RT, RE>(success success: (T) -> RT, failure: (E) -> RE) -> Result<RT, RE> {
        switch self {
        case let .Success(value): return .Success(success(value))
        case let .Error(error): return .Error(failure(error))
        }
    }
}