On this chapter there was nothing interesting from the book, just an implementation of a prefix notation or
Polish notation. In Erlang to solve a problem is made much easier when you break them into small components through which you can then solve individually before piecing everything together. There is also the need to thoroughly understand a problem before starting to code it. Lastly, having tests is important for any program under development as they help make sure everything works fine and will let you change the code without changing the results at the end.
For more information on this topic you can checkout the following amazing posts: