Thanks, that version would work, but agreed - not sure how big of an
improvement that would be over Enum.reduce_while. Trying to think about
this in a more imperative style, it seems that maybe an equivalent of break
is what I'm after? Maybe something close to Ecto's Repo.transaction
semantics?
for foo <- foos do
case barify(foo) do
{:ok, bar} -> bar
{:error, reason} -> break(reason)
end
end
I think this would have to work similarly to how Ecto's transactions work
with Multis, that is return {:ok, bars} or {:error, reason, data_so_far}.
I have found only one usage of Enum.reduce_while in Elixir's codebase.
Interestingly, the shape of the return value is always the same - a list of
finished tests.
https://github.com/elixir-lang/elixir/blob/main/lib/ex_unit/lib/ex_unit/runner.ex#L340
This seems like a separate problem, but maybe something to keep in mind.
Best,
Stefan
wt., 21 gru 2021 o 00:21 Ben Wilson <benwilson...@gmail.com> napisał(a):
> To revisit the example situation from the original post:
>
> ```
> {sections, _acc} =
> for let {section_counter, lesson_counter} = {1, 1}, section <- sections do
> lesson_counter = if section["reset_lesson_position"], do: 1, else:
> lesson_counter
> {lessons, lesson_counter} = for let lesson_counter, lesson <-
> section["lessons"] do
> {Map.put(lesson, "position", lesson_counter), lesson_counter + 1}
> end
> section =
> section
> |> Map.put("lessons", lessons)
> |> Map.put("position", section_counter)
>
> {section, {section_counter + 1, lesson_counter}}
> end
> ```
>
> I think that's nice! It focuses on inputs and outputs and reduces the
> overall line noise.
>
> On Monday, December 20, 2021 at 5:28:29 PM UTC-5 José Valim wrote:
>
>> Stefan, this would work if we include all extensions:
>>
>> for reduce {status, acc} = {:ok, []}, status == :ok, foo <- foos do
>> case barify(foo) do
>> {:ok, bar} -> {:ok, [bar | acc]}
>>
>> {:error, _reason} = error -> error
>> end
>> end
>>
>> I am not sure if you find it any better. It is hard to do this with "let"
>> because you don't want to include the element of when it fails.
>>
>> On Mon, Dec 20, 2021 at 9:23 PM Stefan Chrobot <ste...@chrobot.io> wrote:
>>
>>> I went through some of our code and one thing I'd love to see is a way
>>> to replace Enum.reduce_while with the for comprehension. So the code like
>>> this:
>>>
>>> Enum.reduce_while(foos, {:ok, []}, fn foo, {:ok, bars} ->
>>> case barify(foo) do
>>> {:ok, bar} -> {:cont, {:ok, [bar | bars]}}
>>> {:error, _reason} = error -> {:halt, error}
>>> end
>>> end)
>>>
>>> Would the following even work?
>>>
>>> for reduce(result = {:ok, []}), foo <- foos, {:ok, _} <- result do
>>> case barify(foo) do
>>> {:ok, bar} -> {{:ok, [bar | bars]}}
>>> {:error, _reason} = error -> {error}
>>> end
>>> end
>>>
>>> Even if it did, it's not doing a great job of communicating the intent
>>> and still potentially requires a Enum.reverse call. The intent here is
>>> "early exit with some value upon some condition or pattern mismatch".
>>>
>>>
>>> Best,
>>> Stefan
>>>
>>> pon., 20 gru 2021 o 21:06 Stefan Chrobot <ste...@chrobot.io> napisał(a):
>>>
>>>> I really like this proposal! For me it strikes the perfect balance
>>>> between terseness and explicitness that I've come to enjoy in Elixir.
>>>>
>>>> My votes:
>>>> - Naming: let over given; just because it's shorter,
>>>> - Do use parents: let "feels" similar to var!.
>>>>
>>>> Best,
>>>> Stefan
>>>>
>>>> pon., 20 gru 2021 o 19:54 José Valim <jose....@dashbit.co> napisał(a):
>>>>
>>>>> Good point. I forgot to mention the :reduce option will be deprecated
>>>>> in the long term.
>>>>>
>>>>> On Mon, Dec 20, 2021 at 7:53 PM 'eksperimental' via elixir-lang-core <
>>>>> elixir-l...@googlegroups.com> wrote:
>>>>>
>>>>>> The proposal is very concise,
>>>>>> the only thing that would be problematic is the use of `reduce` for
>>>>>> two
>>>>>> different things,
>>>>>>
>>>>>> for <<x <- "AbCabCABc">>, x in ?a..?z, reduce: %{} do
>>>>>> acc -> Map.update(acc, <<x>>, 1, & &1 + 1)
>>>>>> end
>>>>>>
>>>>>> {sum, count} =
>>>>>> for reduce({sum, count} = {0, 0}), i <- [1, 2, 3] do
>>>>>> sum = sum + i
>>>>>> count = count + 1
>>>>>> {sum, count}
>>>>>> end
>>>>>>
>>>>>> It would lead to misunderstanding as it may not be clear which one we
>>>>>> are talking about when we say "use for reduce"
>>>>>>
>>>>>>
>>>>>> On Mon, 20 Dec 2021 19:11:54 +0100
>>>>>> José Valim <jose....@dashbit.co> wrote:
>>>>>>
>>>>>> > Hi everyone,
>>>>>> >
>>>>>> > This is the second proposal for-let. You can find it in a gist:
>>>>>> > https://gist.github.com/josevalim/fe6b0bcc728539a5adf9b2821bd4a0f5
>>>>>> >
>>>>>> > Please use the mailing list for comments and further discussion.
>>>>>> > Thanks for all the feedback so far!
>>>>>> >
>>>>>>
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