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

[Lennart Augustsson]

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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