StackOverflowError on tail-recursive function

Question
5

Here’s an implementation that works:

def foldRightCPS[T, U](base: U)(f: (T, => U) => U)(as: Seq[T]): U = {
  import scala.util.control.TailCalls._

  @annotation.tailrec
  def _foldRightCPS(fu: U => TailRec[U])(as: Seq[T]): TailRec[U] = {
    as match {
      case Nil => fu(base)
      case head +: next => _foldRightCPS(u => tailcall(fu(f(head, u))))(next)
    }
  }
    
  _foldRightCPS(u => done(u))(as).result
}

It uses scala.util.control.TailCalls. (docs)

There’s a lot to this library that I don’t understand. But could someone explain to me what it is about such an implementation that doesn’t make it subject to the same types of problems?