Perhaps a tutorial where you pick a popular elixir library, identify the relevant data structures, go over how to implement those data structures individually, then in the final section you compose those data structures into a rough version of the finished library. If each project has a defined list of prerequisite data structures the reader needs to know, they can brush up on those topics before completing the rest of the tutorial. This also allows the reader to see how the same data structure can be used in different contexts.
I’m not sure which library you’d choose but I’m not sure it matters that much. You wouldn’t have to handle all the edge cases of whatever you choose as it’s just a learning guide, just cover the big ideas for the problem
thanks.