Example of Functor usage in Cats for a custom type vs standard List

CatFunc.scala

import cats._
import cats.data._
import cats.syntax._
import cats.implicits._

object CatFunc extends App {

   // a very naive linked list implementation and functor for it
  trait MyList[+A]
  case class MyNode[A]( head: A, tail: MyList[A]) extends MyList[A]
  case object MyNil extends MyList[Nothing]

  implicit val functor1=new Functor[MyList]{
    override def map[A, B](fa: MyList[A])(f: A => B): MyList[B] = fa match{
      case MyNode(head, tail)=> MyNode(f(head),map(tail)(f))
      case MyNil => MyNil
    }
  }

  def doStuff[F[_]](li: F[Int])(implicit ev: Functor[F])={
    println(li.map(_+10))
    println(li.void)
    println(li.as(999))
    println(li.tupleLeft(100))
    println(li.tupleRight(200))
    // there is no syntax for ifF, so we use direct from the Functor
    println(ev.ifF(li.map(_>1))(
      "yes", "no"
    ))
  }

  // against a normal List of Ints
  doStuff(List(1,2))

  // against a MyList of Ints
  val li:MyList[Int]=MyNode(1,MyNode(2,MyNil))
  doStuff(li)
  
}

output.txt

List(11, 12)
List((), ())
List(999, 999)
List((100,1), (100,2))
List((1,200), (2,200))
List(no, yes)
MyNode(11,MyNode(12,MyNil))
MyNode((),MyNode((),MyNil))
MyNode(999,MyNode(999,MyNil))
MyNode((100,1),MyNode((100,2),MyNil))
MyNode((1,200),MyNode((2,200),MyNil))
MyNode(no,MyNode(yes,MyNil))