This workshop will be presented at ScalaIO 2019, in Lyon (France), on Tuesday the 29th of October at 9am by Christophe Calvès and I. Welcome. This session will introduce you to a very powerful tool in programming. Whereas most introduction start by presenting its theoretical foundations in a very formal way, we chose to present it via short examples and practical use cases. This workshop is made of three parts. The last one presents three of the most valuable use cases.