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. 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