@m4nl5r I am unsure, because I have seen very
little code using fp-ts what should be done and what shouldn't.

That's why I am trying to see more examples. Especially the other function is
also pure, but might be safer with a more functional aproach:
https://github.com/coderbyheart/adventofcode/blob/0ee6096a995e4f957974d29771bc322180a1bd98/moduleLaunchFuel.ts#L22-L33