# SKB – Scala List parallel

## 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 List par.

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 List par !

I am going to give you an introduction to parallelization. For this, I will be using par.

However, you have to know, that to use this in Scala 2.13+ you need extra steps. You can read more on Stackoverflow. I made the choice to still be using it because, I think, it is a great stepping stone to understand more complex subjects.

Let’s dive in!

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 (8kl0ZPy6T2ycipzz5iNkSg).

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

Compare the output of the two map. In the first one, you see the numbers in the same order they are in the source Range. In the second one, the order is random, try running it several times ; you will see the order of the print statements change.

This happen because all the operation executed in the map happen at the same time, in parallel.

Remember the SKB on Thread.sleep, this was the introduction to the concept of Threads. To allow each operation to happen at the same time, Scala will manage a pool of threads for you. Each operation will be allocated to thread that the computer will compute and then return the result for each operation. Finally, the result will be combined before being returned to you.