Thank you for the reference (not finished it yet).
Worth mentioning functions that can error, should follow the {:ok, response} | {:error, reason} pattern. Because if such a function returns response | {:error, reason}, then if we are inside a with clause and we want to capture the response and use it in the next with clause, such capture value can be either response or {:error, reason} - which goes around the pattern matching.
with response_f1 <- f1(),
{:ok, response_f2} <- f2(response_f1) do
# do something
else
{:error, reason_f1} ->
# we will never come here
# because the returned value from f1
# is already matched to the variable response_f1
end