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> 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> 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 >> >> On Tue, Dec 21, 2021 at 1:29 AM 'eksperimental' via elixir-lang-core < >> 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> 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! >>> > > >>>>>> > >>> > > >>>>>> >>> > > >>>>>> -- >>> > > >>>>>> You received this message because you are subscribed to the >>> > > >>>>>> Google Groups "elixir-lang-core" group. >>> > > >>>>>> To unsubscribe from this group and stop receiving emails from >>> > > >>>>>> it, send an email to elixir-lang-co...@googlegroups.com. >>> > > >>>>>> To view this discussion on the web visit >>> > > >>>>>> >>> https://groups.google.com/d/msgid/elixir-lang-core/61c0d119.1c69fb81.af520.c181SMTPIN_ADDED_MISSING%40gmr-mx.google.com >>> > > >>>>>> . >>> > > >>>>>> >>> > > >>>>> -- >>> > > >>>>> You received this message because you are subscribed to the >>> > > >>>>> Google Groups "elixir-lang-core" group. >>> > > >>>>> To unsubscribe from this group and stop receiving emails from >>> > > >>>>> it, send an email to elixir-lang-co...@googlegroups.com. >>> > > >>>>> To view this discussion on the web visit >>> > > >>>>> >>> 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 >>> > >>> > > >>>>> . >>> > > >>>>> >>> > > >>>> -- >>> > > >>> You received this message because you are subscribed to the >>> > > >>> Google Groups "elixir-lang-core" group. >>> > > >>> To unsubscribe from this group and stop receiving emails from >>> > > >>> it, send an email to 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?utm_medium=email&utm_source=footer >>> > >>> > > >>> . >>> > > >>> >>> > > >> -- >>> > > > You received this message because you are subscribed to the Google >>> > > > Groups "elixir-lang-core" group. >>> > > > To unsubscribe from this group and stop receiving emails from it, >>> > > > send an email to elixir-lang-core+unsubscr...@googlegroups.com. >>> > > > To view this discussion on the web visit >>> > > > >>> 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 >>> > >>> > > > . >>> > > > >>> > > >>> > >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "elixir-lang-core" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to elixir-lang-core+unsubscr...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/elixir-lang-core/61c11ffb.1c69fb81.9b607.f827SMTPIN_ADDED_MISSING%40gmr-mx.google.com >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "elixir-lang-core" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to elixir-lang-core+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4K9WRhyaGpXy8Ds%3DbEq%3DpapgF6w%2BRciB-PY6M6Xe5%2BoFQ%40mail.gmail.com >> <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4K9WRhyaGpXy8Ds%3DbEq%3DpapgF6w%2BRciB-PY6M6Xe5%2BoFQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to elixir-lang-core+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/CACzMe7bYaEzaeeGpiKfux7K%2BLGOGMQS5cdFejqq5%2BEPu056uWA%40mail.gmail.com > <https://groups.google.com/d/msgid/elixir-lang-core/CACzMe7bYaEzaeeGpiKfux7K%2BLGOGMQS5cdFejqq5%2BEPu056uWA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. 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