TailCalls

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
Source
TailCalls.scala
class Object
trait Matchable
class Any

Type members

Classlikes

sealed abstract
class TailRec[+A]

This class represents a tailcalling computation

This class represents a tailcalling computation

Source
TailCalls.scala

Value members

Concrete methods

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

Used to return final result from tailcalling computation

Used to return final result from tailcalling computation

Value Params
`result`

the result value

Returns

a TailRec object representing a computation which immediately returns result

Source
TailCalls.scala
def tailcall[A](rest: => TailRec[A]): TailRec[A]

Performs a tailcall

Performs a tailcall

Value Params
rest

the expression to be evaluated in the tailcall

Returns

a TailRec object representing the expression rest

Source
TailCalls.scala