Example of Tree Functor usage in Cats

output.txt

Branch(990,Leaf(1230),Branch(1000,Leaf(20),Leaf(30)))
Branch(990!,Leaf(1230!),Branch(1000!,Leaf(20!),Leaf(30!)))
Branch(!099,Leaf(!0321),Branch(!0001,Leaf(!02),Leaf(!03)))

TreeFunctorExample.scala

import cats._

object TreeFunctorExample {

  def main(args: Array[String]): Unit = {

    sealed trait Tree[+T]
    case class Leaf[+T](value: T) extends Tree[T]
    case class Branch[+T](value: T, left: Tree[T], right: Tree[T]) extends Tree[T]

    // casting up because of cats invariance
    object Tree {
      def leaf[T](v: T): Tree[T] = Leaf(v)
      def branch[T](v: T, l: Tree[T], r: Tree[T]): Tree[T] = Branch(v, l, r)
    }

    import Tree._

    implicit object TreeFunctor extends Functor[Tree] {
      override def map[A, B](fa: Tree[A])(f: A => B): Tree[B] = fa match {
        case Leaf(v) => Leaf(f(v))
        case Branch(v, l, r) => Branch(f(v), map(l)(f), map(r)(f))
      }
    }

    val tree = branch(99, leaf(123), branch(100, leaf(2), leaf(3)))

    def times10[F[_]](f: F[Int])(implicit func: Functor[F]): F[Int] = func.map(f)(_ * 10)
    def addBang[F[_]](f: F[String])(implicit func: Functor[F]): F[String] = func.map(f)(_+"!")

    val multiplied = times10(tree)
    println(multiplied)

    val excited = addBang(TreeFunctor.map(multiplied)(_.toString))
    println(excited)

    import cats.syntax.functor._

    val reversed=excited.map(_.reverse)
    println(reversed)
  }
}

A similar example, but with a custom LinkedList

https://gist.github.com/fancellu/91a948d1042f996cf843f7090df62ae7