We had discussions in the past and the issue with a Comparable protocol is that we need multiple dispatch. For example, we should be able to semantically compare "Integer cmp Decimal" and "Decimal cmp Integer" which is a more complex problem as it requires defining a scale to compare all of them. Then you can add a compare numbers functionality that converts them to said scale using a separate protocol. It will still require at least two protocol dispatches.
On Sat, Mar 4, 2023 at 7:32 AM Sabiwara Yukichi <sabiw...@gmail.com> wrote: > > It's great that there exists a total order (structural) in > Elixir/Erlang, I just wish it wasn't accessible with `<`, `>`, as it is too > error prone and is simply never what one wants to do (at least in our app). > Elixir 2.0? 😆 > > (another shameless plug) Your comment motivated me to release this project > I was working on: https://github.com/sabiwara/cmp. > Feedback welcome :) > > Le sam. 4 mars 2023 à 01:26, Marc-André Lafortune < > marc-an...@marc-andre.ca> a écrit : > >> It's great that there exists a total order (structural) in Elixir/Erlang, >> I just wish it wasn't accessible with `<`, `>`, as it is too error prone >> and is simply never what one wants to do (at least in our app). Elixir 2.0? >> 😆 >> >> At work I just recently overloaded them to raise unless both arguments >> are `is_number`, and we found bugs where we were comparing Decimals, and >> other bugs where we were comparing with `nil`. They are no longer allowed >> in guards too. >> >> On Friday, 3 March 2023 at 09:31:28 UTC-5 william.l...@cargosense.com >> wrote: >> >>> > if I’m remembering `DateTime.compare/2` correctly >>> >>> Close! The `Module.compare/2` functions return one of `:lt`, `:eq`, or >>> `:gt` ("less than", "equal to", "greater than"), similar to what Haskell >>> does. You may have been thinking of something like OCaml where `compare` >>> returns `-1`, `0`, or `1` resp. >>> >>> > So Why don't we implicitly sort it so that it can be compared by >>> inequality sign(> or <)? >>> >>> To clarify, functions like `<` *define* the sort order. >>> >>> Any time you sort a list, you're using a function that compares two >>> elements. Even if you call `Enum.sort/1`, you're implicitly using `<=/2` as >>> the comparison function. If you want some other sort order, e.g. for >>> semantic ordering of `DateTime`s, then you must supply your own comparison >>> function. >>> >>> The reason that you can use `<` on structs with `CompareChain` is that >>> it uses macros to re-write an expression like >>> >>> `~D[2023-03-03] < ~D[2023-03-04]` >>> >>> as >>> >>> `Date.compare(~D[2023-03-03], ~D[2023-03-04]) == :lt`. >>> >>> But that doesn't change the behavior of `<` itself. We're basically >>> stuck with what `<` and the like do. Though as José points out, that's >>> actually a good thing. >>> >>> (Side note, you actually have to call `compare?(~D[2023-03-03] < >>> ~D[2023-03-04], Date)` with `CompareChain` to invoke the re-write. I just >>> wanted the example to be more readable.) >>> On Friday, March 3, 2023 at 3:27:00 AM UTC-5 José Valim wrote: >>> >>>> It is also important to note that both kinds of comparisons are >>>> important to have in a language. The docs for main discuss this: >>>> https://hexdocs.pm/elixir/main/Kernel.html#module-structural-comparison >>>> >>>> On Fri, Mar 3, 2023 at 7:47 AM Austin Ziegler <halos...@gmail.com> >>>> wrote: >>>> >>>>> In this case, because Elixir is passing the `<` and `>` comparisons to >>>>> the underlying BEAM operations and there’s no overloading to say that >>>>> `left >>>>> < right` should mean `DateTime.compare(left, right) < 0` and `left > >>>>> right` >>>>> should mean `DateTime.compare(left, right) > 0` (if I’m remembering >>>>> `DateTime.compare/2` correctly). >>>>> >>>>> `CompareChain` does that, but it’s something that gets opted into. >>>>> >>>>> -a >>>>> >>>>> On Thu, Mar 2, 2023 at 10:42 PM 최병욱 <cbw...@gmail.com> wrote: >>>>> >>>>>> So Why don't we implicitly sort it so that it can be compared by >>>>>> inequality sign(> or <)? >>>>>> >>>>>> 2023년 3월 3일 금요일 오전 10시 3분 25초 UTC+9에 william.l...@cargosense.com님이 >>>>>> 작성: >>>>>> >>>>>>> Shameless plug: I wrote a library called `CompareChain` that allows >>>>>>> you to use operators like `<` and `>` on structs like `DateTime`. >>>>>>> >>>>>>> Hexdocs: https://hexdocs.pm/compare_chain/readme.html >>>>>>> >>>>>>> On Thursday, March 2, 2023 at 10:54:08 AM UTC-5 Jay Rogov wrote: >>>>>>> >>>>>>>> Because the underlying structure used to represent DateTime is a >>>>>>>> struct, which is simply a map under the hood. >>>>>>>> Erlang/Elixir uses a rather arbitrary order of keys (e.g. hour -> >>>>>>>> year -> day -> minute) when comparing 2 maps which you can't control. >>>>>>>> >>>>>>>> Thus, you need to have a specific function that would compare these >>>>>>>> structs according to implied field order (year -> month -> day -> hour >>>>>>>> -> >>>>>>>> etc.) >>>>>>>> >>>>>>>> More: >>>>>>>> https://hexdocs.pm/elixir/main/NaiveDateTime.html#module-comparing-naive-date-times >>>>>>>> >>>>>>>> On Thursday, 2 March 2023 at 4:38:00 pm UTC+1 cbw...@gmail.com >>>>>>>> wrote: >>>>>>>> >>>>>>>>> Can't you compare DateTime with '>' or '<' instead of >>>>>>>>> DateTime.compare? >>>>>>>>> >>>>>>>> -- >>>>>> 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/afa3830a-8944-4e12-84cc-d8e28d9fceb0n%40googlegroups.com >>>>>> <https://groups.google.com/d/msgid/elixir-lang-core/afa3830a-8944-4e12-84cc-d8e28d9fceb0n%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>> . >>>>>> >>>>> >>>>> >>>>> -- >>>>> Austin Ziegler • halos...@gmail.com • aus...@halostatue.ca >>>>> http://www.halostatue.ca/ • http://twitter.com/halostatue >>>>> >>>>> -- >>>>> 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/CAJ4ekQuHMtqrAVs-kwCo4NQC7vyWV3O8RpAm3c6tgDoiVa%2B5bw%40mail.gmail.com >>>>> <https://groups.google.com/d/msgid/elixir-lang-core/CAJ4ekQuHMtqrAVs-kwCo4NQC7vyWV3O8RpAm3c6tgDoiVa%2B5bw%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/c6f42de3-7132-4a8b-b3fa-4e7b0db67ce2n%40googlegroups.com >> <https://groups.google.com/d/msgid/elixir-lang-core/c6f42de3-7132-4a8b-b3fa-4e7b0db67ce2n%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/CANnyohaRZY_ZRkQ%2BuOP5oHtOTW%3Dwy6vzSNvPiYXT%3D7HP0M2T-g%40mail.gmail.com > <https://groups.google.com/d/msgid/elixir-lang-core/CANnyohaRZY_ZRkQ%2BuOP5oHtOTW%3Dwy6vzSNvPiYXT%3D7HP0M2T-g%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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