My favorite Scala evangelist is trying to reinvent the wheel in caching.

He enjoys playing with monads and fancy terms like side-effects, but forgets about software development basics -- clearly defining real-world problem that he is trying to solve:
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Dennis: Do you mean you do not support a scenario when multiple users are requesting your web app ~simultaneously?
ivan_gandhi: I do not condone sharing code with effects between threads.
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It is not clear whether his code is supposed to work in multi-thread environment (like serving incoming web requests from multiple users) or in single-thread (like outgoing requests from a single thread service).
It is not clear whether he wants to reuse cache between parallel threads or not.
The end result -- code without purpose. Such purposeless code is impossible to meaningfully evaluate.
On the other hand such approach gives a lot of room for inventing Cartesian product of input source and time segments.

My takeaway from it is that Scala inspires excessive FP games and therefore distracts developers from solving real-life problems.