`count_while` would imply (to me) that it counts while a predicate returns true. The only name I can think of that would be expressive and consistent with other Enum functions would be something like `Enum.count_take` or `Enum.take_count`, but I think that `Enum.take_until` is a better name.
On Friday, December 4, 2020 at 10:50:18 AM UTC-5 mario.luis...@gmail.com wrote: > This would be the first function in Enum with "until" in its name. For > consistency with the other functions in this module, wouldn't it be > preferable the "while" suffix instead ? > > A sexta-feira, 4 de dezembro de 2020 à(s) 07:29:29 UTC, José Valim > escreveu: > >> We can also add Enum.count_until(enumerable, filter, n) and you can use >> filter = & &1 if you want to force enumeration, like there is for >> Enum.count/2 today. >> >> On Fri, Dec 4, 2020 at 8:28 AM José Valim <jose....@dashbit.co> wrote: >> >>> That's a very good point Jayson. I think we should go with "count until >>> should take advantage of all optimizations and ignore side-effects”. I >>> believe it is fair to expect that no enumerable that implements count >>> actually has side-effects, exactly because of the implications of what you >>> said. >>> >>> On Fri, Dec 4, 2020 at 8:08 AM 'Jayson Vantuyl' via elixir-lang-core < >>> elixir-l...@googlegroups.com> wrote: >>> >>>> There are three questions I don’t think we’re considering: >>>> * What does it mean to “partially count” an Enumerable that implements >>>> an “efficient” `count/1` function? >>>> * If such an Enumerable has side-effects for its `reduce/3` function, >>>> should they be somehow still happen even though the `count/1` doesn’t >>>> necessarily iterate the elements? >>>> * If such an Enumerable returns a larger count that asked for, should >>>> we return the larger “technically correct” value; or the `max + 1` value? >>>> >>>> I generally like `count_until/2` because it‘s unopinionated about what >>>> you’re doing with the count. But the answers to the above question >>>> probably >>>> should be addressed and documented. >>>> >>>> I really see two ways to address the above question. Either we consider >>>> “count until implies actively counting” or “count until should take >>>> advantage of all optimizations and ignore side-effects”. >>>> >>>> My feel is that the latter is generally going to be more efficient in >>>> the common case but the former is less likely to create unexpected >>>> behavior >>>> from people who don’t know how their Enumerable is implemented. >>>> >>>> I’m inclined to favor the former. It won’t throw away efficiency that a >>>> custom Enumerable will implement, it’ll generally make naive code faster, >>>> and the rare cases where people expect side-effects is probably less >>>> important than either of those other benefits. >>>> >>>> Sent from my iPhone >>>> >>>> On Dec 3, 2020, at 21:18, José Valim <jose....@dashbit.co> wrote: >>>> >>>> >>>> Thanks Allen! I believe that's a good idea. >>>> >>>> I think the main insight is that we don't want a predicate function >>>> (at_least? more_than?). Using compare returns three states - which is >>>> better than two - but what if we just returned the number? After all, if I >>>> am interested in knowing if something has less than 10, 10, or more than >>>> 10, I just need to count until eleven. Returning a number seems to be more >>>> flexible too. Therefore, what do you think about: count_until(enum, value)? >>>> >>>> To check if less, eq, or more than 10: >>>> >>>> case Enum.count_until(count, 10 + 1) do >>>> 11 -> :gt >>>> 10 -> :eq >>>> _ -> :lt >>>> end >>>> >>>> For at least 10: >>>> >>>> Enum.count_until(count, 10) == 10 >>>> >>>> For more than 10: >>>> >>>> Enum.count_until(count, 10 + 1) > 10 >>>> >>>> Thoughts? >>>> >>>> >>>> On Fri, Dec 4, 2020 at 2:14 AM Zach Daniel <zachary....@gmail.com> >>>> wrote: >>>> >>>>> Yep! I really like it :) >>>>> >>>>> On Thu, Dec 3, 2020 at 7:52 PM eksperimental <eksper...@autistici.org> >>>>> wrote: >>>>> >>>>>> On Thu, 3 Dec 2020 19:06:18 -0500 >>>>>> Allen Madsen <allen.c...@gmail.com> wrote: >>>>>> >>>>>> > Enum.compare_count([], 1) #=> :lt >>>>>> > Enum.compare_count([1], 1) #=> :eq >>>>>> > Enum.compare_count([1, 2], 1) #=> :gt >>>>>> >>>>>> This is the way to go, because in one function call we can determine >>>>>> the >>>>>> course of the action, such as in >>>>>> >>>>>> case Enum.compare_count(list, n) do >>>>>> :lt -> ... >>>>>> :eq -> ... >>>>>> :gt -> ... >>>>>> end >>>>>> >>>>>> when using the predicate functions it would require at least two >>>>>> function calls. >>>>>> >>>>>> > >>>>>> > Allen Madsen >>>>>> > http://www.allenmadsen.com >>>>>> > >>>>>> > >>>>>> > On Thu, Dec 3, 2020 at 6:51 PM Zach Daniel >>>>>> > <zachary....@gmail.com> wrote: >>>>>> > >>>>>> > > Well, List.count doesn’t exist yet, but either way it sounds like >>>>>> > > not a great idea :) I couldn’t find examples in other Lang’s, so >>>>>> > > maybe I’ll just throw out some other names: >>>>>> > > >>>>>> > > Enum.at_least?/2 >>>>>> > > >>>>>> > > Enum.at_most?/2 >>>>>> > > >>>>>> > > Enum.has_count?/2 >>>>>> > > >>>>>> > > On Thu, Dec 3, 2020 at 5:14 PM Michał Muskała <mic...@muskala.eu> >>>>>> > > wrote: >>>>>> > > >>>>>> > >> Unfortunately this can’t be done automatically since it has >>>>>> subtle >>>>>> > >> semantic differences. In particular Enum.count/1 (or length/1) >>>>>> not >>>>>> > >> only traverses the list to count its size, but also verifies it’s >>>>>> > >> a proper list raising an exception for improper lists. The >>>>>> > >> difference could be seen for value like: >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> [1, 2, 3 | :invalid] >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> Calling length/1 or Enum.count/1 on this raises. If compiler did >>>>>> > >> the optimisation you propose, for something like length(list) > >>>>>> 0, >>>>>> > >> it wouldn’t fully traverse the list and wouldn’t raise. Thus such >>>>>> > >> an optimisation is not possible in the general case. >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> *From: *elixir-l...@googlegroups.com < >>>>>> > >> elixir-l...@googlegroups.com> >>>>>> > >> *Date: *Thursday, 3 December 2020 at 22:04 >>>>>> > >> *To: *elixir-l...@googlegroups.com < >>>>>> > >> elixir-l...@googlegroups.com> >>>>>> > >> *Subject: *Re: [elixir-core:9802] Proposal `Enum.more_than?/2` or >>>>>> > >> `List.more_than?/2` >>>>>> > >> >>>>>> > >> This probably off the table/unreasonable, but it also seems like >>>>>> > >> something that could be statically solved and people would never >>>>>> > >> need to know as it is just an optimization. E.g Enum.count(list) >>>>>> > >>>>>> > >> n could optimized by the compiler? Probably wouldn’t be good for >>>>>> > >> all Enums, since counting would be expected to enumerate them, so >>>>>> > >> maybe only something like List.count 🤷♂️ >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> On Thu, Dec 3, 2020 at 1:42 PM Zach Daniel >>>>>> > >> <zachary....@gmail.com> wrote: >>>>>> > >> >>>>>> > >> Another benefit to the options list would be supporting it for >>>>>> > >> count with a predicate, e.g Enum.count(enum, &some_predicate/1, >>>>>> > >> max: 4) >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> On Thu, Dec 3, 2020 at 1:35 PM Zach Daniel >>>>>> > >> <zachary....@gmail.com> wrote: >>>>>> > >> >>>>>> > >> Nothing is jumping out at me from elsewhere yet, but another >>>>>> > >> option might be accepting options in `Enum.count`, like >>>>>> > >> `Enum.count(list, max: 4)`. I’ll keep searching though. >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> On Thu, Dec 3, 2020 at 1:31 PM Zach Daniel >>>>>> > >> <zachary....@gmail.com> wrote: >>>>>> > >> >>>>>> > >> I agree on the name feeling subpar :) I’ll take a look and see if >>>>>> > >> I can find other examples. >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> On Thu, Dec 3, 2020 at 12:21 PM José Valim <jose....@dashbit.co> >>>>>> > >> wrote: >>>>>> > >> >>>>>> > >> Thanks Zach! I like this idea but the proposed name, for some >>>>>> > >> reason, doesn't sit right with me. Is there any prior art from >>>>>> > >> other langs we could look at? >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> On Thu, Dec 3, 2020 at 6:15 PM Zachary Daniel >>>>>> > >> <zachary....@gmail.com> wrote: >>>>>> > >> >>>>>> > >> Counting a list, especially a large one, to know if there are >>>>>> > >> "more than x" or "less than x" items is inefficient. >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> Right now I often see things like `if Enum.count(list) > 4 ...`, >>>>>> > >> mostly because writing a recursive `more_than?` check is tedious, >>>>>> > >> or doing something like `Enum.empty?(Enum.drop(list, 4))` is not >>>>>> > >> very expressive. >>>>>> > >> >>>>>> > >> >>>>>> > >> >>>>>> > >> I think it would be nice to have an `Enum.more_than?` that does >>>>>> > >> that work for you. It could also be `List.more_than?/2` if we >>>>>> > >> don't want it in Enum. Any thoughts? >>>>>> > >> >>>>>> > >> -- >>>>>> > >> 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/263d7c39-a32b-4294-93d8-40f248c9b3c8n%40googlegroups.com >>>>>> > >> < >>>>>> https://groups.google.com/d/msgid/elixir-lang-core/263d7c39-a32b-4294-93d8-40f248c9b3c8n%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-co...@googlegroups.com. >>>>>> > >> To 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