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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://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)
}
}
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