Scala example source code file (Bind.scala)

This example Scala source code file (Bind.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

apply, bind, bindlaw, boolean, equal, need

The Bind.scala Scala example source code

package scalaz

////
/**
 * An [[scalaz.Apply]] functor, where a lifted function can introduce
 * new values _and_ new functor context to be incorporated into the
 * lift context.  The essential new operation of [[scalaz.Monad]]s.
 *
 * @see [[scalaz.Bind.BindLaw]]
 */
////
trait Bind[F[_]] extends Apply[F] { self =>
  ////

  /** Equivalent to `join(map(fa)(f))`. */
  def bind[A, B](fa: F[A])(f: A => F[B]): F[B]

  override def ap[A, B](fa: => F[A])(f: => F[A => B]): F[B] = {
    val fa0 = Need(fa)
    bind(f)(x => map(fa0.value)(x))
  }

  /** Sequence the inner `F` of `FFA` after the outer `F`, forming a
   * single `F[A]`. */
  def join[A](ffa: F[F[A]]) = bind(ffa)(a => a)

  // derived functions

  /**
   * `if` lifted into a binding.  Unlike `lift3((t,c,a)=>if(t)c else
   * a)`, this will only include context from the chosen of `ifTrue`
   * and `ifFalse`, not the other.
   */
  def ifM[B](value: F[Boolean], ifTrue: => F[B], ifFalse: => F[B]): F[B] = {
    val t = Need(ifTrue)
    val f = Need(ifFalse)
    bind(value)(if(_) t.value else f.value)
  }

  /** Pair `A` with the result of function application. */
  def mproduct[A, B](fa: F[A])(f: A => F[B]): F[(A, B)] =
    bind(fa)(a => map(f(a))((a, _)))

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

  trait BindLaw extends ApplyLaw {
    /**
     * As with semigroups, monadic effects only change when their
     * order is changed, not when the order in which they're
     * combined changes.
     */
    def associativeBind[A, B, C](fa: F[A], f: A => F[B], g: B => F[C])(implicit FC: Equal[F[C]]): Boolean =
      FC.equal(bind(bind(fa)(f))(g), bind(fa)((a: A) => bind(f(a))(g)))

    /** `ap` is consistent with `bind`. */
    def apLikeDerived[A, B](fa: F[A], f: F[A => B])(implicit FB: Equal[F[B]]): Boolean =
      FB.equal(ap(fa)(f), bind(f)(f => map(fa)(f)))
  }
  def bindLaw = new BindLaw {}

  ////
  val bindSyntax = new scalaz.syntax.BindSyntax[F] { def F = Bind.this }
}

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

  ////

  ////
}