Not necessarily that they are replaceable,
but that pattern of :cont, :halt, :suspend is most commonly used via
Enumerable.reduce
On Mon, 20 Dec 2021 19:18:53 -0500
"'eksperimental' via elixir-lang-core"
<elixir-lang-core@googlegroups.com> wrote:
> > 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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