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-lang-core@googlegroups.com <elixir-lang-core@googlegroups.com> Date: Thursday, 3 December 2020 at 22:04 To: elixir-lang-core@googlegroups.com <elixir-lang-core@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.s.dan...@gmail.com<mailto:zachary.s.dan...@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.s.dan...@gmail.com<mailto:zachary.s.dan...@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.s.dan...@gmail.com<mailto:zachary.s.dan...@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.va...@dashbit.co<mailto:jose.va...@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.s.dan...@gmail.com<mailto:zachary.s.dan...@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-core+unsubscr...@googlegroups.com<mailto:elixir-lang-core+unsubscr...@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-core+unsubscr...@googlegroups.com<mailto:elixir-lang-core+unsubscr...@googlegroups.com>. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4JX4NE1yWH1G5L_DjF18v8zejF0%2BSkb_oz%3DPiUHM8Mz1w%40mail.gmail.com<https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4JX4NE1yWH1G5L_DjF18v8zejF0%2BSkb_oz%3DPiUHM8Mz1w%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<mailto:elixir-lang-core+unsubscr...@googlegroups.com>. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/CAK-yb0BBGCrgbZamFs%2BeqLUis6mFQgvUHkKK1htSN5rDDWwMRQ%40mail.gmail.com<https://groups.google.com/d/msgid/elixir-lang-core/CAK-yb0BBGCrgbZamFs%2BeqLUis6mFQgvUHkKK1htSN5rDDWwMRQ%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/DB7PR07MB3899C92933992464F17898E1FAF20%40DB7PR07MB3899.eurprd07.prod.outlook.com.
