SKB – Scala Monad


This article is part of the Scala knowledge bits Series.

Periodically, I will publish new exercises so you can slowly build up knowledge about Scala.

It is designed to be done in a very short amount of time and learn a little bit each day, just to create a routine.

This episode will teach you about Scala Monad.

Hope you are going to enjoy it! It is designed for anyone to learn Scala from scratch and slowly learn, one Bit at a time.

After this Bit, I would love to hear your feedback in the comments down below.

Feel free to join the Discord server as well if you would like some help and support from the rest of our community.

What are we learning today?

Today we are going to learn about Scala Monad !

We have done a lot in those last months !

Today is the day Monad stops being scary.

Time to try on the exercise on your own and scroll down for more information when you are done or if you are stuck.


Here is an exercise to complete today.

If I did my job well, you should be able to guess by yourself the solution based on what you previously learned and based on the clues.

But if you get stuck, scroll down to get more information.

The goal of the exercise is to replace the ??? by a piece of code so that the exercise compiles and that’s how you win! Good luck!

You can fill the exercise right in here:

Or, if it does not load, go on to Scastie (JB0wl7zzQxiefAf4EwfzBA).

More information about Scala Monad

In this exercise you will learn (or have learned, if you have already solved the puzzle) about Scala Monad.

We already learned about Functor, Foldable, Applicative, and Traversable.

We have almost encountered all the beast of Category Theory at this point. Today we are going to tackle Monad.

As you can see, it is simply a Functor and Applicative, with one extra feature: flatten. Which allows us to define the world famous flatMap. As you can see in the definition, flatMap is simply map followed by flatten.

When you look at the implementation, we only need a few concept defined:

  • map: which describe how to apply a transformation to the inner type A of the wrapper F.
  • pure: which describe how to wrap a A into a F[A]
  • flatten: which describe how to compact F[F[A]] in to F[A]

Those concepts are all that needed to enable complex behavior like filter or flatMap.

I also wanted to show off what we learned in the last episode about TypeClasses with the implicit object and the implicit class which allow us to give a shortcut for the function we want to use often.

As always, if you have any questions, reach out on Discord !

Feel free to go back to the exercise, modify the code to try out new things and get a better intuition for Scala Monad.


I hope you have learned something new or had fun during this Scala Knowledge Bit.

Please ask questions or post feedback in the comments below.

The next Scala knowledge bit is coming in a few days ! Come back soon to check it out.

If you are curious about the previous Scala knowledge Bits, go check it out! 🙂

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