Getting aquainted with a new langauge. Really wish there was a splatter operator.

car_cdr.playground

func car<T>(l: Array<T>?) -> T? {
    if l == nil || l!.count <= 0 {
        return nil
    } else {
        return l![0]
    }
}

func cdr<T>(l: Array<T>?) -> Array<T>? {
    if l == nil || l!.count <= 1 {
        return nil
    } else {
        return Array<T>(l![1..l!.count])
    }
}

var beverly_hills = [9,0,2,1,0]

car(beverly_hills) //9
cdr(beverly_hills) //[0,2,1,0]

var ingredients = ["sugar", "flower", "eggs", "water"]

car(ingredients) //"sugar"
cdr(ingredients) //["flower", "eggs", "water"]

//Almost empty
car([3.14]) // 3.14
cdr([3.14]) //nil

//Empty
car(Double[]()) //nil
cdr(Double[]()) //nil

//A summing function implemented using:
func sum(numbers: Array<Int>?, answer: Int = 0) -> Int {
    let first = car(numbers)

    if first == nil {
        return answer
    } else {
        return answer + sum(cdr(numbers), answer: first!)
    }
}

sum([1,2,3,4,5]) //15

Allowed for the passing of optional arrays so I could implement a sum function.