An accumulator function written in Swift.

accumulator.swift

// accumulator function

func accumulator(initial: Int, incrementBy: Int) -> () -> Int {
    var value = initial
    func accum() -> Int {
        value += incrementBy
        return value
    }
    return accum
}

// example usage 

var myAccumulator = accumulator(0, 1)
myAccumulator() // => 1
myAccumulator() // => 2
myAccumulator() // => 3
myAccumulator() // => 4
myAccumulator() // => 5