Reactive Programming in Kotlin

High-order functions

Those functions that take another function as an argument or return a function as result are called high-order functions. Consider the following example to understand it better:

    fun highOrderFunc(a:Int, validityCheckFunc:(a:Int)->Boolean) {//(1) 
      if(validityCheckFunc(a)) {//(2) 
        println("a $a is Valid") 
      } else { 
        println("a $a is Invalid") 
      } 
    } 
 
    fun main(args: Array<String>) { 
      highOrderFun(12,{ a:Int -> a.isEven()})//(3) 
      highOrderFunc(19,{ a:Int -> a.isEven()}) 
    } 

In this program, we've declared a highOrderFunc function, which will take an Int and a validityCheckFunc(Int) function. We are calling the validityCheckFunc function inside the highOrderFunc function, to check whether the value was valid or not. However, we are ...