Here is an example of nested Functions. The first function solves if two numbers are divisible, if not it returns nil. The second function makes an optional binding and return the answer. In this function there is the return of the first function as parameter.

CodeExample: nested Function.swift

func divideIfWhole(_ value: Int, by divisor: Int) -> Int? {
    var answer: Int? = 0
    let divisible = value % divisor
    switch divisible {
    case 0:
         answer = value / divisor
    default:
         answer = nil
    }
    return answer
}

let divisilbe = divideIfWhole


func isItDivisible(_ divisilbe: (Int, Int) -> Int?, _ a: Int, _ b: Int) {
    if let result = divideIfWhole(a, by: b) {
    print("Yep, it divides \(result) times")
    }else{
        print("Not divisible :[")
    }
}



isItDivisible(divisilbe, 10, 2)