I would stick to your first version. It is clear what the returned errors are, the code is clean and concise.
Introducing functions to have functions is overkill.
The idea behind the anti-pattern is when you have multiple functions returning the same error tuples for different situations. If you have 2 fetch functions that both return {:error, :not_found} then you don’t know where it came from, that has to be avoided.
Therefore the suggestion is to return distinct tuples, which you already do.
It will always be a matter of taste. I for example have a with clause with 9 different else-clauses but they all differ and are clear where they originate.
). I have found that strictly adhering to two-tuples for results (ok / error) and then deconstructing the 2nd element if/when the need calls for it leads to much more predictable code.
