Ackermann is being studied for recursion. It is quite complex to do TCO for Ackermann. However, there have been some implementation of Ackermann in Haskell with TCO

Ackermann.scala

/*
http://blog.aunndroid.com/2011/11/learning-scala-recursion-and-tco-1.html

Ackermann is being studied for recursion. It is quite complex to do TCO for Ackermann.
However, there have been some implementation of Ackermann in Haskell with TCO
http://lambda-the-ultimate.org/node/2673
*/
object Ackermann {
	def main(args : Array[String]) : Unit = {
		println(args.toList);
		if (args.isEmpty) { printUsage(); return }
		val numberStrList = args.toList.foldLeft(List[String]()) {
			(iList, str) =>
				iList :+ str.foldLeft("") {
					case (str, ch) if (ch.isDigit) => str + ch
					case (str, ch) => str
				}
		}
		val numberList = numberStrList.foldLeft(List[Int]()) {
			(l, str) => l :+ str.toInt
		}.take(2)
		println(numberList)
		if (numberList.length < 2) printUsage()
		else {
			val result = ackerMann(numberList.head, numberList.last)
			printResult((numberList.head, numberList.last), result)
		}
	}

	def ackerMann(m : BigInt, n : BigInt) : BigInt = {
		if (m == 0) return n + 1
		if (m > 0 && n == 0) return ackerMann(m - 1, 1)
		ackerMann(m - 1, ackerMann(m, n - 1))
	}

	def printUsage() = {
		val m = 3
		val n = 2
		println("Usage is:")
		println("scala AckerMann.scala " + m + " " + n)
		val result = ackerMann(m, n)
		printResult((m, n), result)
	}

	def printResult(in : (Int, Int), r : BigInt) = {
		println("Ackermann value for " + in + " is : " + r)
	}

}