The next two Elixir releases, v1.6 and v1.7, will include a code formatter and a property-based testing functionality as part of the standard library. The code formatter is built on top of document algebra, an idea introduced by Hughes in "The Design of a Pretty-Printing Library", and property-based testing is based on the QuickCheck paper, by Claessen and Hughes. In this talk, we will approach those two very useful features from the implementation perspective, learning what changed compared to the original papers. More details on website here: http://www.elixirconf.eu/elixirconfeu2018/jose-valim