Consider this code:

with {:a, first_result} <- {:a, List.first(["apple"])},
      {:b, b} <- {:b, %{} |> to_string} do
  {:ok, "happy path"}
else
  {:a, _} -> {:error, "this will never be a problem"}
  {:b, error} -> {:error, "Why can I not print #{first_result} here?"}
end

I have learned by trial-and-error that this code will not return

{:error, "Why can I not print apple here?"}

as I originally expected from this kind of syntax. Instead, the compiler tells me that first_result is not defined in the else block. It makes sense, because the “clause chain” returns the error result of the failing clause.

So I have 2 questions:

1. What is the best way to achieve the desired outcome? Should I just use two separate case expressions?
2. Imagine if the first clause adds something to the database with Repo.insert. Does Ecto know it is inside a with expression and wait for all clauses to succeed before committing the transaction? That seems unlikely. So then, why does this expression not allow us to access any successful results?

It seems like I should be very careful when using with since, if I understand correctly (I probably don’t), I can have “partial success” without being able to see the successful results.

Any advice and insight is welcome! I hope the question is clear.

P.S. I have already read https://hexdocs.pm/elixir/Kernel.SpecialForms.html#with/1. It just says “the chain is aborted”.

P.P.S. get your SO points here: https://stackoverflow.com/questions/63394081/advice-for-working-around-my-only-problem-with-with-expressions-accessing