Functor

category_Category.scala

package sun.flower.category

/**
 * 
 * User: sunflower
 * Date: 13-1-26
 * Time: 下午4:02
 * 
 */



object Category{

  //def id[A](a: A) = a  // map is functions




  trait Category[-->[_,_]]{

    def id[A] : A --> A
    def compos[A,B,C](f: A => B, g : B => C) : A --> C


  }

  class MyCategory extends Category[Function]{
    def id[A]: A => A = a => a
    def compos[A,B,C]( f : A => B, g :  B => C ) : A => C = g compose f
  }


  def main(args: Array[String]) {

  }

}

category_MyFunctors.scala

package sun.flower.category

/**
 * 
 * User: sunflower
 * Date: 13-1-26
 * Time: 下午4:45
 * 
 */
object MyFunctors {

  trait Functor[-->[_,_], -->>[_,_], F[_]]{

    def fmap[A,B](f : A --> B) : F[A] -->> F[B]

  }

  object Functor{

    def fmap[A,B,F[_]](xs : F[A])( f : A => B)(implicit functor : MyFunctor[F]) : F[B] =
      functor.fmap(f)(xs)


    trait MyFunctor[F[_]] extends Functor[Function,Function,F]

    implicit object ListFunctor extends MyFunctor[List]{
      def fmap[A,B](f : A => B) : List[A] => List[B] = _ map f
    }

    implicit object OptionFunctor extends  MyFunctor[Option]{
      def fmap[A,B](f: A => B) : Option[A] => Option[B]  = _ map f
    }

  }

  def main(args: Array[String]) {
    println(Functor.fmap(List(1,2,3))( _ + 1 ))
  }



}