SKB – Scala Recursion


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 Recursion.

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 Recursion !

Recursion is a major tool in the toolbox of the software engineer.

It can allow to describe a problem from a different perspective.

In the context of Functional Programming this is also a major trick to avoid using mutable variables.

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 (Cnic9MRTRE2BgIR3NAC5Zg).

More information about Scala Recursion

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

This is a very basic example to be able to understand the concept of recursion fully. In the future, we will see more complex application of recursion.

To build a successful recursion, you need several things:

  • Stopping condition: this is the most important thing. Without it the recursion will keep going for ever and eventually fail with an exception: StackOverflowError.
  • The method needs to call itself. In this example, you can see the loop function is called inside of itself.
  • Increment: something needs to change when calling the function again, otherwise, same as without a stopping condition, the code will never stop running since the stopping condition will never get reached. In this example you can see that when loop is called, it is called with modified arguments.
  • Most of the time you will have some kind of accumulator that hold the final result of the computation. In our example, this would be the argument named acc.
  • Initial condition: we also need a starting value for the accumulator and the other arguments that might be required to perform the computation. In this example, we need to set acc equals to 0.

The most famous example of recursion in books are always factorial or Fibonacci. I would love to see your implementation, feel free to submit a Scastie link in the comment section or 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 Recursion.


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.

Feel free to try on the next Scala Knowledege Bit.

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

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