scala.util.control

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" http://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
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Cont[A, B]Done[A]Call[A]TailRec[A]
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Type Members

  1. case class Call[A](rest: () ⇒ TailRec[A]) extends TailRec[A] with Product with Serializable

    Internal class representing a tailcall

  2. case class Cont[A, B](a: TailRec[A], f: (A) ⇒ TailRec[B]) extends TailRec[B] with Product with Serializable

    Internal class representing a continuation with function A => TailRec[B].

  3. case class Done[A](value: A) extends TailRec[A] with Product with Serializable

    Internal class representing the final result returned from a tailcalling computation

  4. abstract class TailRec[+A] extends AnyRef

    This class represents a tailcalling computation

Value Members

  1. final def !=(arg0: Any): Boolean

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  2. final def ##(): Int

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  3. final def ==(arg0: Any): Boolean

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  4. final def asInstanceOf[T0]: T0

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  5. def clone(): AnyRef

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

    Used to return final result from tailcalling computation

    Used to return final result from tailcalling computation

    returns

    a TailRec object representing a computation which immediately returns result

  7. final def eq(arg0: AnyRef): Boolean

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  8. def equals(arg0: Any): Boolean

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  9. def finalize(): Unit

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  10. final def getClass(): Class[_]

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  11. def hashCode(): Int

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  12. final def isInstanceOf[T0]: Boolean

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  13. final def ne(arg0: AnyRef): Boolean

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  14. final def notify(): Unit

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  15. final def notifyAll(): Unit

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  16. final def synchronized[T0](arg0: ⇒ T0): T0

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  17. def tailcall[A](rest: ⇒ TailRec[A]): TailRec[A]

    Performs a tailcall

    Performs a tailcall

    rest

    the expression to be evaluated in the tailcall

    returns

    a TailRec object representing the expression rest

  18. def toString(): String

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  19. final def wait(): Unit

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  20. final def wait(arg0: Long, arg1: Int): Unit

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  21. final def wait(arg0: Long): Unit

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