Scala example source code file (Arrows.scala)

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

Java - Scala tags/keywords

a, a, applicativearrow, applicativearrows, arr, arr, arrow, arrows, b, b, c, c, m, monad

The Scala Arrows.scala source code

package scala.tools.scalap
package scalax
package rules

trait Arrows extends UnitFunctors  {
  type Arr[-A, +B] <: Arrow[A, B]
  type M[+B] = Arr[Nothing, B]
  
  def arrow[A, B](f : A => B) : Arr[A, B]
  def diag[A] = arrow[A, (A, A)] { a => (a, a) }
  
  override def unit[B](b : => B) : M[B] = arrow { any : Any => b }
  
  trait Arrow[-A, +B] extends Functor[B] { this : Arr[A, B] =>
    
    def map[C](f : B => C) = comp(arrow(f))
    def comp[C](bc : => Arr[B, C]) : Arr[A, C]
    def fst[C] : Arr[(A, C), (B, C)]
  }
}

trait ApplicativeArrows extends Arrows {
  type Arr[-A, +B] <: ApplicativeArrow[A, B]

  def app[A, B] : Arr[(Arr[A, B], A), B]
  
  trait ApplicativeArrow[-A, +B] extends Arrow[A, B] { self : Arr[A, B] =>
    def flatMap[SubA <: A, C](f : B => Arr[SubA, C]) : Arr[SubA, C] =
      diag[SubA].comp(map(f).fst[SubA]).comp(app[SubA, C])
  }
}

trait ArrowMonads extends ApplicativeArrows with Monads {
  type Arr[-A, +B] <: ApplicativeArrow[A, B] with Monad[B]

  override def unit[A](a : => A) : M[A] = arrow[Unit, A](Unit => a)
}