Ben, That is how const is used in Haskell. Although without currying I don’t see how it is useful. I’m waiting to see an example that drives it home. I agree with Bruce about naming concepts but I don’t see the concept as useful in Elixir.
Bruce, do you have a code sample using the idea? Amos King CEO Binary Noggin > On Feb 4, 2020, at 07:35, Ben Wilson <benwilson...@gmail.com> wrote: > > > Addendum: I re-read the proposal because the const/1 vs const/2 thing > confused me, and I'm seeing both in play there. The spec is arity 2, the > example right after though is arity 1, and the Enum example is arity 2 but > without a constant value. The Enum example perhaps makes the most sense, > because you could do: > > ``` > Enum.map([1,2,3,4], &const(&1, :foo)) > ``` > which would return `[:foo, :foo, :foo, :foo]` effectively replacing the > contents of the list with all `:foo`. Is that the idea? > >> On Tuesday, February 4, 2020 at 8:16:53 AM UTC-5, Ben Wilson wrote: >> I agree with Michal. Additionally, I'm not clear how `const/1` could be used >> in Bruce's example at all. >> >> To elaborate, `fn -> foo() end` and `const(foo())` cannot be equivalent >> when `const/1` is merely a function. This becomes readily apparent when >> `foo()` is side effects or side causes. In the first case, `foo()` is never >> evaluated until the wrapping function is called, in the case of `const/1` >> however the function is evaluated and then its return value bound over by a >> function. Eg: `fn -> DateTime.utc_now() end` will always return the current >> time when evaluated, where as `const(DateTime.utc_now())` will evaluate the >> current time once and then always return that same time. >> >> That might sound useful, except that we already can do that by simply >> binding the return value of `DateTime.utc_now()` to a variable and passing >> that variable around. I'm having difficulty coming up with a scenario where, >> instead of simply having the value, I have the value wrapped in an anonymous >> function that I need to call. >> >> Consequently, I struggle to see where `const/1` can actually be used, or how >> it would work. In the example in the initial proposal, there is this: >> >> ``` >> Enum.map([0,1,2,3], &Function.const/2) >> ``` >> >> As a minor note, presumably that should be `const/1`, right? More >> importantly, what is the return value here? If it's `[0, 1, 2, 3]` then >> `const/1` is equivalent to `identity`. If it's >> >> ``` >> [fn -> 1 end, fn -> 2 end, fn -> 3 end, fn -> 4 end] >> ``` >> >> then a simple list of integers seems universally more useful. >> >>> On Tuesday, February 4, 2020 at 5:03:39 AM UTC-5, Michał Muskała wrote: >>> I’d argue back that this particular pattern, where you want a list of fixed >>> length with the same value, is much better served by `List.duplicate/2`. >>> >>> >>> >>> I think in general, higher order combinator functions like identity, const, >>> flip, and friends are usually used to facilitate the point-free style of >>> programming in languages like Haskell. And in general point-free style >>> usually does not lead to the most readable code. >>> >>> >>> >>> Again, referring to the example provided, if I know anonymous functions, I >>> know what’s going on. When using `Funcion.const`, I have to understand that >>> concept as well. There’s one extra thing to learn. >>> >>> >>> >>> Michał. >>> >>> >>> >>> From: "elixir-l...@googlegroups.com" <elixir-l...@googlegroups.com> on >>> behalf of Bruce Tate <br...@grox.io> >>> Reply to: "elixir-l...@googlegroups.com" <elixir-l...@googlegroups.com> >>> Date: Monday, 3 February 2020 at 11:47 >>> To: "elixir-l...@googlegroups.com" <elixir-l...@googlegroups.com> >>> Subject: Re: [elixir-core:9353] [Proposal] Add Function.const/2 >>> >>> >>> >>> My counterpoint is this. Any time you can name a concept that makes it >>> easier to see what's going on, it's important. >>> >>> >>> >>> Examples: >>> >>> * Create back padding of four blank table cells >>> >>> * use with Stream.repeatedly and take, for example, to initialize a data >>> structure for OTP. >>> >>> >>> >>> I do these two things with pretty good frequency because I build responsive >>> layouts often needing tabular structure, but without HTML tables. >>> >>> >>> >>> Say you are laying out tables that are responsive but without HTML tables. >>> You >>> >>> d want to add padding to the end of uneven rows. To create the padding >>> you'd do >>> >>> >>> >>> Stream.repeatedly( fn -> :padding end) |> Enum.take(4) >>> >>> >>> where :padding is the constant padding you want. This pattern comes up with >>> some regularity in my user interfaces. It doesn't hurt anything, and it >>> would be a great addition to the function module. >>> >>> >>> >>> I like this proposal. This is exactly the kind of function you'd expect to >>> see in the module. >>> >>> >>> >>> +1 from me. >>> >>> >>> >>> -bt >>> >>> >>> >>> On Sun, Feb 2, 2020 at 2:42 PM Jesse Claven <jesse...@gmail.com> wrote: >>> >>> That all makes sense! I would say that in Elm it's used somewhat >>> frequently. I don't have access to the previous code that I worked on >>> (changed jobs), so unfortunately I'm unable to grep for `always` to find >>> some good examples. >>> >>> >>> >>> In the codebase at my new job, there's a couple of places where `fn _ -> >>> something` is (my original example in this thread). It's basically for >>> anywhere you'd want to ignore some value, and always return something else. >>> I tried searching through GitHub for that code sample but the search >>> functionality was a little subpar. >>> >>> >>> >>> I understand about keeping the stdlib small, but for a relatively small >>> function, and one that's considered "table stakes" in most FP languages, >>> perhaps it would be a good fit? >>> >>> >>> On Thursday, 30 January 2020 11:20:58 UTC, Wiebe-Marten Wijnja wrote: >>> >>> The reason `Function.identity/1` was added after it was requested many >>> times previously, was that at some point everyone agreed that it would >>> improve Elixir's documentation, because it is easier to search for than >>> `&(&1)`. >>> >>> The `const` pattern is much less wide-spread. In e.g. Haskell it sees some >>> use in places where it is the single (or at least by far the simplest) way >>> to make things typecheck in a pure functional environment. >>> >>> In Elixir, I suspect that it would be used much less commonly. The fact >>> that our functions contain statements that are executed from top to bottom >>> and rebindable variable names means that we are even less likely to use it >>> anywhere. >>> >>> As such, I don't think `const` is a function that is important enough to >>> include in the standard library. >>> >>> >>> >>> Of course, I'm very much open to evidence of the contrary ^_^. Do you have >>> any example code of where you'd see `const` being useful? >>> >>> >>> >>> ~Marten/Qqwy >>> >>> On 30-01-2020 10:24, Jesse Claven wrote: >>> >>> Hey Amos, >>> >>> >>> >>> Ah that's right. Every now and then I'm reminded that Elixir doesn't >>> support currying when I try to do something haha Your suggestion makes >>> sense. >>> >>> >>> >>> Would there be any downsides to having it, even if it isn't the most >>> incredible function? Again to call on the `Function.identity/1`, and it's >>> discussion, it's useful when it's useful for concise and semantic code. >>> >>> >>> On Wednesday, 29 January 2020 22:43:51 UTC, Amos King - Binary Noggin wrote: >>> >>> Jesse, >>> >>> >>> >>> I see where you are going, but Elixir doesn't have currying. For instance, >>> the last example you gave will return an error. >>> >>> >>> >>> You could make it work by changing it a bit. >>> >>> >>> >>> `@spec const(a) :: fn(any() -> a) when a: var` >>> >>> >>> >>> So, const would return an fn instead of taking two arguments. I don't know >>> how useful that would be in the long run. I know it is common in function >>> programming, but I don't see it being extremely helpful in Elixir. >>> >>> >>> >>> I'm ready to be convinced. >>> >>> >>> >>> Cheers, >>> >>> >>> >>> Amos King >>> >>> CEO >>> >>> Binary Noggin >>> >>> http://binarynoggin.com #business >>> >>> https://elixiroutlaws.com #elixir podcast >>> >>> http://thisagilelife.com #podcast >>> >>> ======================================================= >>> I welcome VSRE emails. Learn more at http://vsre.info/ >>> ======================================================= >>> >>> >>> >>> >>> On Wed, Jan 29, 2020 at 4:01 PM Jesse Claven <jesse...@gmail.com> wrote: >>> >>> Hey everyone! >>> >>> I propose adding `Function.const/2` as a function which for argument `x`, >>> would always return `x`. >>> >>> ``` >>> @spec const(any(), any()) :: any() >>> def const(_original_value, new_value), do: new_value >>> ``` >>> >>> This is somewhat similar to the new `Function.identity/1` in that it may >>> seem like we've easily lived without it, but it does afford some more >>> concise/semantic ways to represent a common pattern. >>> >>> ``` >>> fn _ -> something_else() end >>> ``` >>> >>> This would become: >>> >>> ``` >>> const(something_else()) >>> ``` >>> >>> ``` >>> Enum.map([0,1,2,3], &Function.const/2) >>> ``` >>> >>> I'm new to Elixir, so I'm not sure of the weight that the name `const` >>> would carry, so there could be a more acceptable name. >>> >>> If accepted, I'd be happy to create a PR! >>> >>> Equivalents in other languages: >>> >>> - Haskell: >>> https://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Function.html#v:const >>> - PureScript: >>> https://pursuit.purescript.org/packages/purescript-const/4.1.0/docs/Data.Const >>> - Elm: https://package.elm-lang.org/packages/elm/core/latest/Basics#always >>> - Scala: >>> https://www.scala-lang.org/api/current/scala/Function$.html#const[T,U](x:T)(y:U):T >>> >>> - Idris: >>> https://www.idris-lang.org/docs/current/prelude_doc/docs/Prelude.Basics.html#Prelude.Basics.const >>> >>> >>> >>> Thanks for your time. >>> >>> >>> >>> -- >>> 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-l...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/elixir-lang-core/576949a3-93e2-4117-b1f1-ab4621f10e88%40googlegroups.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-l...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/elixir-lang-core/f8b6009d-e21a-434a-96e0-e2c6ae3c1a0e%40googlegroups.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-l...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/elixir-lang-core/294d4f77-6b91-4316-a152-0c209fad12db%40googlegroups.com. >>> >>> >>> >>> >>> >>> -- >>> >>> >>> >>> Regards, >>> >>> Bruce Tate >>> >>> CEO >>> >>> >>> >>> >>> >>> >>> >>> Groxio, LLC. >>> >>> 512.799.9366 >>> >>> br...@grox.io >>> >>> grox.io >>> >>> -- >>> 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-l...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/elixir-lang-core/CAFXvW-6%3DfheYjjyQ7xiWYkP0B0t%2BfoGae9OGtkDDSvSpD4s_Sg%40mail.gmail.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-core+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/1a49eabe-6509-41c7-b425-21e207737472%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. 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