Accumulator factory

class Accumulator(sum) {
    method add(num) {
        sum += num
    }
}
 
var x = Accumulator(1)
x.add(5)
Accumulator(3)
say x.add(2.3)               # prints: 8.3

The same thing can be achieved by returning a closure from the Accumulator function.

func Accumulator(sum) {
    func(num) { sum += num }
}
 
var x = Accumulator(1)
x(5)
Accumulator(3)
say x(2.3)                  # prints: 8.3