According to Idea this function doesn't contain a ...

# announcements

[bascan]

According to Idea this function doesn't contain a tail call. Any idea why?

tailrec fun increment(i: Int): Int =
    if (i == 3) i
    else i + increment(i + 1)

[todd.ginsberg]

Because the last call is the + not the increment function call

[Ashutosh Panda]

what is a tail call

[eekboom]

lmgtfy:

[eekboom]

https://www.baeldung.com/kotlin-tail-recursion

[bascan]

@todd.ginsberg I factored the + out, but still got the same warning. What else could be wrong?

tailrec fun increment(i: Int): Int =
    if (i == 3) i
    else {
        val j = i + 1
        i + increment(j)
    }

[sikri]

Tail recursion is when last action is evaluation of the same function.
In your code for else branch last action is NOT increment(j), but adding i to result of increment.
Therefore, there is no tail recursion, as on stack should exist value of i and code should know about adding operation

[marstran]

If you want to make that function tail recursive, you have to add an accumulator as a parameter. That will allow you to make the recursive call last. Something like this:

fun increment(i: Int): Int {
  tailrec fun innerIncrement(i: Int, acc: Int): Int =
    if (i == 3) i + acc
    else innerIncrement(i + 1, acc + i)

  return innerIncrement(i, 0)
}

[sikri]

tailrec fun increment(i: Int, acc: Int = 0): Int {
   return if (acc == 3) acc
  else {  
    val j = i + 1  
    increment(j, acc + j)
 }
}

[marstran]

The wrapper function is just to keep the function signature the same.

[sikri]

maybe that’s what you want

[bascan]

@marstran @sikri Thanks for your snippets. I think I got it now, cheers.