Functor — incompatible types

Here's a handy tidbit for handling types in Functors. From: Functor — incompatible types - Google Groups:

trait Functor[F[_],A] { 
  def map[B](f: A => B): F[B] 
}
 
case class Box[T](val content: T) extends Functor[Box, T] {
  def map[B](f: T => B): Box[B] = Box(f(content))
  override def toString = "Box(" + content + ")"
}