I want to do ln(N!) in Scala with tailrec

  @tailrec
  final def recursiveLogN(n: Int): Double = {
    if (n <= 1) {
      return 0
    }
    Math.log(n)   recursiveLogN(n - 1)
  }

The compile error:

could not optimize @tailrec annotated method recursiveLogN: it contains a recursive call not in tail position
    Math.log(n)   recursiveLogN(n - 1)

CodePudding user response：

The recursive call should be the last method call, the way your snippet is written it is just part of the last expression.

It can be rewritten to something like:

  @tailrec
  final def recursiveLogN(n: Int, accum: Double = 0): Double = {
    if (n <= 1) {
      return accum
    }
   recursiveLogN(n - 1, accum  Math.log(n))
  }

And then tail call elimination will be possible