Re: Is there a function \x -> (x, x) in standard libraries?

On 2019-07-16 23:21, Dan Burton wrote:

+1 for "dup", if it is to be included at all.

Same here. --Andreas

On Tue, Jul 16, 2019 at 12:56 PM Vladislav Zavialov mailto:vladislav@serokell.io> wrote:

It is reasonably common. I have grepped Hackage using https://codesearch.aelve.com/haskell/ and

* \x->(x,x) occurs 203 times * join (,) occurs 53 times * id &&& id occurs 22 times

It also pops up in discussions as a counter-example of a linear function:

dup :: a ->. (a,a) dup x = (x,x)  -- does not typecheck with -XLinearTypes!

I think it should be added under the name "dup" (short for “duplicate”).

- Vlad

> On 16 Jul 2019, at 22:29, Lennart Augustsson mailto:lennart@augustsson.net> wrote: > > It's not harmful, but is it common enough to have a name? > > On Tue, Jul 16, 2019, 12:28 Ignat Insarov mailto:kindaro@gmail.com> wrote: > So, it is not considered harmful. Then I propose we add it to > Data.Tuple under a humane name. > > On Tue, 16 Jul 2019 at 19:41, Lennart Augustsson mailto:lennart@augustsson.net> wrote: > > > > Or 'join (,)' > > > > On Tue, Jul 16, 2019, 09:26 Zemyla mailto:zemyla@gmail.com> wrote: > >> > >> id &&& id > >> > >> On Tue, Jul 16, 2019, 10:58 Ignat Insarov mailto:kindaro@gmail.com> wrote: > >>> > >>> Hello. > >>> > >>> I wonder if there is a function like \x -> (x, x) in the standard libraries. > >>> > >>> I looked up in Hoogle. It gave me links: > >>> > >>> 1. https://hackage.haskell.org/package/utility-ht/docs/Data-Tuple-HT.html#v:dou... > >>> 2. https://hackage.haskell.org/package/extra/docs/Data-Tuple-Extra.html#v:dupe > >>> 3. https://hackage.haskell.org/package/relude/docs/Relude-Extra-Tuple.html#v:du... > >>> > >>> None of these is to the standard library. I wonder if there is an > >>> intentional omission for some important reason? If not, I think this > >>> function should be added to Data.Tuple. > >>> > >>> I know some of the persons that make decisions here like Category > >>> theory, so I point out this function is mentioned in Categories for > >>> the Working Mathematician, as δ, the diagonal function, on page 3 > >>> (second edition), although set with angular brackets. > >>> > >>> Have a great day. > >>> _______________________________________________ > >>> Libraries mailing list > >>> Libraries@haskell.org mailto:Libraries@haskell.org > >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries > >> > >> _______________________________________________ > >> Libraries mailing list > >> Libraries@haskell.org mailto:Libraries@haskell.org > >> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries > _______________________________________________ > Libraries mailing list > Libraries@haskell.org mailto:Libraries@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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