*Guides Feedback*
These look excellent, should make the power of *for* much more accessible.
*let Feedback*
I like the functionality of this proposal much more!
I will say, I'm still not a fan of using new qualifiers. I'm not sure why
we need to introduce a new special form for this, since we can do whatever
we need to in the macro? What's wrong with:
> for count = 0, count < 5, x <- element do {x, count + 1} end
Perfectly matches traditional for loops, and pattern matching in function
arguments, with all the familiar errors/warning possibly emitted from
them, while keeping the bodies identically functionally-refactorable. No
*let*s needed.
Re:* for reduce*, since *for* already has idiomatic keyword arguments to
further modify functionality, isn't *:reduce* is doing fine as is? We'd
just document how it interacts with for-bindings.
> Furthermore, the introduction of let and reduce qualifiers opens up the
option for new qualifiers in the future, such as for async that is built on
top of Task.async_stream/3.
>
> Async doesn't have its own arguments
<https://gist.github.com/josevalim/fe6b0bcc728539a5adf9b2821bd4a0f5#naming>
Similarly, I'm unsure what's wrong with add an *async: true* keyword
argument. It's just behaviour configuration, not something we need to bring
to the forefront as a pattern match?
*Replies*
> I am against the notion of `for_let` and `for_reduce`. I see that as
using up more of the special forms "namespace".
Agreed, mirroring my misgivings about "for let" and "for reduce".
On Tuesday, December 21, 2021 at 11:58:19 AM UTC-5 gva...@gmail.com wrote:
> I'm a vote in favor of the proposal. I think I have a slight preference
> for the parens. But it's very slight, and I'm not sure I wouldn't change my
> mind after using it for a while.
>
> I am against the notion of `for_let` and `for_reduce`. I see that as using
> up more of the special forms "namespace".
>
> I'm slightly disappointed that the old style `reduce:` option will be
> deprecated (because I have old code I'll have to update) however, the
> change does make things more consistent and I appreciate the thought about
> future extensions to for comprehensions.
>
> -Greg Vaughn
>
> PS. I just watched your latest Twitch stream. I wish I could have been
> there live to hear you read the dictionary and to offer obscure English
> words to the bikeshed discussion :-D
>
> On Dec 21, 2021, at 3:31 AM, José Valim <jose....@dashbit.co> wrote:
>
> 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-l...@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-l...@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 <benwil...@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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>> > > >>>>>> To view this discussion on the web visit
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>> > > >>>>>> .
>> > > >>>>>>
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>> > > >>>>> <
>> 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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>> 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
>> >
>> > > >>> .
>> > > >>>
>> > > >> --
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>> > > > To unsubscribe from this group and stop receiving emails from it,
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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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