In this case it is not so easy to read because I haven’t refactored it into a nicer format yet. But sometimes you need to do many things in succession and handle all of their failures. Then with helps you to avoid a pyramid of nested conditionals. I know my code is not the best example but here is one with that has more things going on:
with {:ok, %DateTime{} = datetime} <- parse_timestamp(timestamp),
{:ok, datetime} <- check_datetime_diff(datetime),
{:ok, offset} <- get_offset(timestamp),
{:ok, %Pulse{} = pulse} <- create_pulse(user, machine, datetime, offset),
{:ok, inserted_xps} <- create_xps(pulse, xps) do
# Broadcast XP data to possible viewers on profile page and frontpage
ProfileChannel.send_pulse(user, %{pulse | xps: inserted_xps})
# Coordinates are not sent for private profiles
coords = if user.private_profile, do: nil, else: GeoIPPlug.get_coords(conn)
FrontpageChannel.send_pulse(coords, %{pulse | xps: inserted_xps})
conn |> put_status(201) |> json(%{ok: "Great success!"})
else
{:error, :not_found, reason} ->
conn |> put_status(404) |> json(%{error: reason})
{:error, :generic, reason} ->
conn |> put_status(400) |> json(%{error: reason})
{:error, :internal, reason} ->
conn |> put_status(500) |> json(%{error: reason})
end
Here you can see the happy path is easily readable and the error handling is after it, and there is no nesting.
