Scala Functor and Monad differences

Question

Can please someone explain the differences between Functor and Monad in the Scala context?

Answer 1

The best article laying out in details those two notions is "The Essence of the Iterator Pattern " from Eric Torreborre's Blog.

Functor

trait Functor[F[_]] {
  def fmap[A, B](f: A => B): F[A] => F[B]
}

• One way of interpreting a Functor is to describe it as a computation of values of type A.
  For example:
  
  • List[A] is a computation returning several values of type A (non-deterministic computation),
  • Option[A] is for computations that you may or may not have,
  • Future[A] is a computation of a value of type A that you will get later, and so on.
• Another way of picturing it is as some kind of "container" for values of type A.

It is the basic layer from which you define:

• PointedFunctor (to create a value of type F[A]) and
• Applic (to provide a method applic, being a computed value inside the container F (F[A => B]), to apply to a value F[A]), Applicative Functor (aggregation of an Applic and a PointedFunctor).

All three elements are used to define a Monad.