Simple Functor

simple_functor.scala

// Functors appear to be type converters for type constructors
trait Functor[T[_]] {
  def apply[A](x: A) : T[A]
  def map[A,B](x: T[A])(f: A => B) : T[B]
}

// Simple Demo with Functors
object FunctorDemo extends App {

  val listInt = List(1,2,3,4,5,6)

  // In this simple example, i'm trying to convert a list of 'Int's
  // to a list of 'Double's. The key function is the 'map' where it 
  // transform a type of 'Int' to 'Double'
  val converter = new Functor[List] {
    def apply[Double](x: Double) : List[Double] = List(x)
    def map[Int, Double](x: List[Int])(f: Int => Double) : List[Double] = { 
        for (i <- x ) yield f(i)
    }   
  }
                                                                                                                    
  val listDouble = converter.map(listInt)(_.toDouble)

  println("We're going to convert a list of 'int' to list of 'double'")
  println("before -> " + listInt)
  println("after  -> " + listDouble)

}