Question

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

Answer 1

Scala itself really does not emphasize the Functor and Monad terms that much. I guess using map is the functor side, using flatMap is the Monad side.

For me looking and playing around with scalaz has been so far the best avenue to get a sense of those functional concepts in the scala context (versus the haskell context). Two years ago when I started scala, the scalaz code was gibberish to me, then a few months ago I started looking again and I realized that it’s really a clean implementation of that particular style of functional programming.

For instance the Monad implementation shows that a monad is a pointed functor because it extends the Pointed trait (as well as the Applicative trait). I invite you to go look at the code. It has linking in the source itself and it’s really easy to follow the links.

So functors are more general. Monads provide additional features. To get a sense of what you can do when you have a functor or when you have a monad, you can look at MA

You’ll see utility methods that need an implicit functor (in particular applicative functors) such as sequence and sometime methods that needs a full monad such as replicateM.