class LLInt { static var zero: LLInt = LLInt(0) let isPositive: Bool? let prev: LLInt? var value: Int { guard let positive = isPositive, let previous = prev else { return 0 } if positive { return 1 + previous.value } else { return -1 + previous.value } } init(_ value:Int) { if value == 0 { prev = nil isPositive = nil } else if value > 0 { prev = LLInt(value - 1) isPositive = true } else { prev = LLInt(value + 1) isPositive = false } } }