> I have found only one usage of Enum.reduce_while in Elixir's codebase.
This is because under the hood Enum.reduce_while is a call
`Enumerable.reduce/3`, so we are invoking this functions direcly.
On Tue, 21 Dec 2021 00:47:44 +0100
Stefan Chrobot <ste...@chrobot.io> wrote:
> 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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