Higher-order function and recursive call

1

Hi , I want to implement a function, that returns a function with recursive call on itself. An Example: recursive calculation of compound interest

fun interest(end: Double, inc: Double) = {(start: Double, i: Int) ->
    if(start >= end) i
    else // here i want to call the function
}

a simple function that works now is

fun interest(start: Double, end: Double, inc: Double, i: Int = 0): Int {
    if(start >= e) return i
    else return interest(start + start * inc / 100,end, inc, i + 1)
}

so the best looking code would be 

fun interest(end: Double, inc: Double) = {(start: Double, i: Int = 0) ->
    if(start >= end) i
    else (start + start * inc / 100, i + 1)
}
val f = interest(2000, 1)



f(1000)

f(500)

…


Here are two things, that are not working right now:

  1. default value
  2. recursive call

2

Kotlin can't do what you want exactly, but I think you can get close with a named local function

3

Thx for the hint with the local function.

This is a solution i’m happy with:

``

fun interest(end: Double, inc: Double) : (Double) -> Int{

  fun interest(start: Double, i: Int): Int {

  if(start >= end) i

  else interest(start + start * inc / 100, i + 1)

  }

  return {(start: Double): Int -> interest(start, 0)}

}


val f = interest(2000.0, 1.0)

println(f(1000.0))

println(f(500.0))

4

You can make it a bit shorter by removing the type annotations on the return line:

``

    return {start -> interest(start, 0)}