All right, I am facing another thing that is somewhat of a challenge.
Naming things is truly one of the hardest problems of a Computing Scientist.
I have created Extractable and Insertable and they work well. But now I’d like to build abstractions on top of these protocols. These abstractions being part of the original protocol-defining libraries does not make sense, because there might be more, different abstractions that could be built on top.
I’m probably going to create a library called Collection that contains common functionality on collections. Collection will probably depend on FunLand, Extractable and Insertable. The interface of the Collectionmodule itself will probably look similar to Enumerable, with the difference that any collection in the output of its functions is not converted into a list.
If there is a better approach, please tell me 
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Alongside of this, I am currently working more on the Okasaki queues, and also started building some simple tree implementations.
