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

[Lennart Augustsson]

It's not harmful, but is it common enough to have a name?

On Tue, Jul 16, 2019, 12:28 Ignat Insarov <kindaro at 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 <lennart at augustsson.net>
> wrote:
> >
> > Or 'join (,)'
> >
> > On Tue, Jul 16, 2019, 09:26 Zemyla <zemyla at gmail.com> wrote:
> >>
> >> id &&& id
> >>
> >> On Tue, Jul 16, 2019, 10:58 Ignat Insarov <kindaro at 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:double
> >>> 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:dupe
> >>>
> >>> 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.
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> >>
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