gistfile1.txt

func sum(a: Int?, b: Int?) -> Int? {
    a.flatMap({ unwrappedA in
        b.flatMap({ unwrappedB in
            .some(unwrappedA + unwrappedB)
        })
    })
}

func sum(_ a: [Int], _ b: [Int]) -> [Int] {
    a.flatMap({ unwrappedA in
        b.flatMap({ unwrappedB in
            [unwrappedA + unwrappedB]
        })
    })
}