# SKB – Scala Functor

## Introduction

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 Functor.

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 Functor !

Functional Programming today !

And let’s start by the easiest one: Functor.

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

## Exercise

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.

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 (lPfrjWhhQUew9oxzlD0nSw).

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

In this episode, we are focusing on the Functor.

The formal definition for a Functor is a transformation from a category `A` to a category `B`. Such transformations are often represented by an arrow: `A -> B`.

This transformation, in Scala, is translated to the method `map` that we have seen a lot in the past.

A Functor (`F`), in category theory, must follow several rules:

• All element of `A` must have a result in `B`
• Identity:
• If we define `id`, the identity method: `id(a) == a`,
• then `id(F) == F.map(id)`.
• Composition:
• If we define `f` and `g`, two methods,
• then `F.map(f).map(g) == F.map( g(f(_)) )`.

In the following episode, we are going to learn more about the other component of the category theory ecosystem and functional programming overall.

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

## Conclusion

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