object TailCalls

Methods exported by this object implement tail calls via trampolining. Tail calling methods have to return their result using done or call the next method using tailcall. Both return a TailRec object. The result of evaluating a tailcalling function can be retrieved from a Tailrec value using method result. Implemented as described in "Stackless Scala with Free Monads" https://blog.higher-order.com/assets/trampolines.pdf

Here's a usage example:

import scala.util.control.TailCalls._ def isEven(xs: List[Int]): TailRec[Boolean] = if (xs.isEmpty) done(true) else tailcall(isOdd(xs.tail)) def isOdd(xs: List[Int]): TailRec[Boolean] = if (xs.isEmpty) done(false) else tailcall(isEven(xs.tail)) isEven((1 to 100000).toList).result def fib(n: Int): TailRec[Int] = if (n < 2) done(n) else for { x <- tailcall(fib(n - 1)) y <- tailcall(fib(n - 2)) } yield x + y fib(40).result
class Object
trait Matchable
class Any

Type members


sealed abstract class TailRec[+A]

This class represents a tailcalling computation

Value members

Concrete methods

def done[A](result: A): TailRec[A]

Used to return final result from tailcalling computation

Value Params

the result value


a TailRec object representing a computation which immediately returns result

def tailcall[A](rest: => TailRec[A]): TailRec[A]

Performs a tailcall

Value Params

the expression to be evaluated in the tailcall


a TailRec object representing the expression rest