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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 <
>>>> [email protected]> 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 <[email protected]> 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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>>>>> .
>>>>>
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>>>>
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>>>>
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>>
> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/elixir-lang-core/CACzMe7aXBL1jNM_aWmJJzYOjrK%3Dtf-4%2BLPLJLpccu_G4zr0cAg%40mail.gmail.com
>>
>> <https://groups.google.com/d/msgid/elixir-lang-core/CACzMe7aXBL1jNM_aWmJJzYOjrK%3Dtf-4%2BLPLJLpccu_G4zr0cAg%40mail.gmail.com?utm_medium=email&utm_source=footer>
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>
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