The one thing I have in the back of my mind is that what I enjoy about elixir
is the explicitness. This feels like it might trick people into thinking that
there is mutable data or something, which isn't the case.
In the examples given I can't see how they are different from using reduce with
a tuple as an accumulator, eg:
```
for i <- [1, 2, 3], reduce: {0, 0} do
{doubled, sum} -> {i * 2, i + sum}
end
```
I'm possibly missing something but I worry that it hides what's actually
happening!
Best
Adam
> On 21 Dec 2021, at 12:35, Bruce Tate <br...@grox.io> wrote:
>
> Minus one for me on for_let and for_reduce naming as this style of concept
> composition limits the number of concepts we can add later. I like the rest
> of the latest proposal as stated, and I like the idea of deferring the
> match-while semantics.
>
> -bt
>
> On Tue, Dec 21, 2021 at 5:23 AM José Valim <jose.va...@dashbit.co
> <mailto:jose.va...@dashbit.co>> wrote:
> At the moment the early-exit semantics will be as described in the proposal.
> In the future, we can make the left side of "let" be a pattern, so it
> automatically exits as soon as it doesn't match the pattern. We could
> introduce non-local returns but I think they would not be accepted for the
> same reason implicit variables were not.
>
> In any case, I would like to move those to a separate discussion, as there is
> already a lot to unpack here.
>
> > As for the parens, I was actually in favor of keeping them.
>
> I am mostly reflecting the current preferences but there is one argument for
> not having parens, which is if we were to introduce async. Async doesn't have
> its own arguments, so it would be `for async(), x <- collection`, which
> doesn't look nice. for_let and for_reduce may be a discussion worth having
> though.
>
>
>
> On Tue, Dec 21, 2021 at 10:58 AM Stefan Chrobot <ste...@chrobot.io
> <mailto:ste...@chrobot.io>> wrote:
> Any thoughts about adding the early-exit semantics?
>
> As for the parens, I was actually in favor of keeping them. "for let" and
> "for reduce" seem like different variants of "for", which raises the question
> if maybe they should be "for_let" and "for_reduce" instead.
>
> Does this mean that the formatter will drop the parens?
>
> Best,
> Stefan
>
> wt., 21 gru 2021 o 10:31 José Valim <jose.va...@dashbit.co
> <mailto:jose.va...@dashbit.co>> napisał(a):
> Compared to the previous proposal, this one has been very quiet so far. :) I
> am unsure if it was because it was a Monday or because holidays are coming,
> so I am sending a ping.
>
> ALso note I updated the proposal to not use parens around let/reduce, which
> seems to be the preference so far:
> https://gist.github.com/josevalim/fe6b0bcc728539a5adf9b2821bd4a0f5
> <https://gist.github.com/josevalim/fe6b0bcc728539a5adf9b2821bd4a0f5>
> On Tue, Dec 21, 2021 at 1:29 AM 'eksperimental' via elixir-lang-core
> <elixir-lang-core@googlegroups.com
> <mailto:elixir-lang-core@googlegroups.com>> wrote:
> 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
> <mailto: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 <mailto: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
> > >
> > > <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
> > > <mailto: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 <mailto: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
> > > >>> <mailto: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
> > > >>>> <mailto: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
> > > >>>>> <mailto: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 <mailto: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
> > > >>>>>> >
> > > >>>>>> > <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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> > > >>>>>
> > > >>>>> <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4LOyoAmXULJQo%2BYX4eFVJZJAoYtKHytoHujCS_kJ6AEuA%40mail.gmail.com>
> > > >>>>> <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4LOyoAmXULJQo%2BYX4eFVJZJAoYtKHytoHujCS_kJ6AEuA%40mail.gmail.com?utm_medium=email&utm_source=footer
> > > >>>>>
> > > >>>>> <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4LOyoAmXULJQo%2BYX4eFVJZJAoYtKHytoHujCS_kJ6AEuA%40mail.gmail.com?utm_medium=email&utm_source=footer>>
> > > >>>>> .
> > > >>>>>
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> > > >>> <mailto:elixir-lang-co...@googlegroups.com>.
> > > >>>
> > > >> 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>
> > > >>> <https://groups.google.com/d/msgid/elixir-lang-core/CACzMe7aXBL1jNM_aWmJJzYOjrK%3Dtf-4%2BLPLJLpccu_G4zr0cAg%40mail.gmail.com?utm_medium=email&utm_source=footer
> > > >>>
> > > >>> <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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> > > >
> > > > <https://groups.google.com/d/msgid/elixir-lang-core/c1fea9e2-f47c-4236-812a-431bc7d76d62n%40googlegroups.com>
> > > > <https://groups.google.com/d/msgid/elixir-lang-core/c1fea9e2-f47c-4236-812a-431bc7d76d62n%40googlegroups.com?utm_medium=email&utm_source=footer
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