Scala example source code file (BindRec.scala)

This example Scala source code file (BindRec.scala) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" ^TM.

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Java - Scala tags/keywords

bindlaw, bindrec, bindreclaw, boolean, equal, productbindrec

The BindRec.scala Scala example source code

package scalaz

////
/**
 * [[scalaz.Bind]] capable of using constant stack space when doing recursive
 * binds.
 *
 * Implementations of `tailrecM` should not make recursive calls without the
 * `@tailrec` annotation.
 *
  * Based on Phil Freeman's work on stack safety in PureScript, described in
  * [[http://functorial.com/stack-safety-for-free/index.pdf Stack Safety for
  * Free]].
 */
////
trait BindRec[F[_]] extends Bind[F] { self =>
  ////

  def tailrecM[A, B](f: A => F[A \/ B])(a: A): F[B]

  override def forever[A, B](fa: F[A]): F[B] =
    tailrecM[Unit, B](u => map(fa)(_ => -\/(u)))(())

  /**The product of BindRec `F` and `G`, `[x](F[x], G[x]])`, is a BindRec */
  def product[G[_]](implicit G0: BindRec[G]): BindRec[λ[α => (F[α], G[α])]] =
    new ProductBindRec[F, G] {
      def F = self
      def G = G0
    }

  trait BindRecLaw extends BindLaw {
    def tailrecBindConsistency[A](a: A, f: A => F[A])(implicit FA: Equal[F[A]]): Boolean = {
      val bounce = tailrecM[(Boolean, A), A] {
        case (bounced, a0) =>
          if (!bounced)
            map(f(a0))(a1 => -\/((true, a1)))
          else
            map(f(a0))(\/.right)
      }((false, a))

      FA.equal(bind(f(a))(f), bounce)
    }
  }
  def bindRecLaw = new BindRecLaw {}

  ////
  val bindRecSyntax = new scalaz.syntax.BindRecSyntax[F] { def F = BindRec.this }
}

object BindRec {
  @inline def apply[F[_]](implicit F: BindRec[F]): BindRec[F] = F

  ////

  ////
}