This is a currying example for Swift 4.2

Currying.swift

func sum(v1: Int, v2: Int) -> Int {
    return v1 + v2
}

func sub(v1: Int, v2: Int) -> Int {
    return v1 - v2
}

func operation (_ operation: @escaping (Int, Int) -> Int) -> (Int, Int) -> Int {
    return { v1, v2 in
        operation(v1, v2)
    }
}

func multiple(_ operations: ((Int, Int) -> Int)...) -> (Int, Int) -> [Int] {
    return { v1, v2 in
        operations.map({ op in
            op(v1,v2)
        })
    }
}

let sumOp = operation(sum) // (Int, Int) -> Int
let subOp = operation(sub) // (Int, Int) -> Int
operation(sum)(4,2) // 6
operation(sub)(4,2) // 2
sumOp(4,2) // 6
subOp(4,2) // 2
multiple(sumOp,subOp)(4,2) // [6,2]