Enum.map with error handling

enumex.ex

defmodule EnumEx do

  @doc """
  Executes `fun` for each `list` element (just like `map`), but if one iter fails,
  then aborts everything and returns first error.
  `fun` must return {:ok, result} | {:error, error}
  """
  def map_or_error(list, fun) do
    result = Enum.reduce(list, [], fn
      i, acc when is_list(acc) ->
        IO.inspect {i, acc}
        case fun.(i) do
          {:ok, res} -> [res | acc]
          {:error, _error} = error -> error
        end
      _i, {:error, _error} = error -> error
    end)
    case result do
      {:error, _error} = error -> error
      list when is_list(list) -> {:ok, Enum.reverse(list)}
    end
  end

  @doc """
  Example of usage
  """
  def map_or_error_test do
    f = fn
      6 -> {:error, :error6}
      i -> {:ok, i}
    end
    {:ok, [1,2,3,4,5]} = map_or_error 1..5, f
    {:error, :error6} = map_or_error 1..6, f
  end
end