Applying functional programming to the ReactiveCalculator class

So, now, after trying to understand the ReactiveCalculator class from the previous chapter, we will try to optimize the code as well. Let's first take a look at the init block of the ReactiveCalculator class:

    init{ 
      nums = Pair(a,b) 
 
      subjectAdd.map({ it.first+it.second }).subscribe({println
      ("Add = $it")} )//1 
      subjectSub.map({ it.first-it.second }).subscribe({println
      ("Substract = $it")} ) 
      subjectMult.map({ it.first*it.second }).subscribe
      ({println("Multiply = $it")} ) 
      subjectDiv.map({ it.first/(it.second*1.0) }).subscribe
      ({println("Divide = $it")} ) 
 
      subjectCalc.subscribe({ 
        with(it) { 
          calculateAddition() 
          calculateSubstraction() 
          calculateMultiplication() 
          calculateDivision() 
        } 
      }) 
 
      subjectCalc.onNext(this) 
     } 

So, now, with the knowledge of functional programming, we can easily...