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

-1 We already have a 'dup' function defined in base but it does something completely different. I see no reason to add a mild abbreviation and force Haskellers to add yet another silly word to their vocabulary. Library authors can already create their own set of vocabulary by importing a common internal module. Base doesn't need to get involved. On Wed, Jul 24, 2019 at 10:06 AM Cale Gibbard wrote:

The advantage of (\x->(x,x)) as a name is that for a small number of additional characters, the meaning is obvious even if you didn't know that this thing existed before, and it generalises nicely -- to other tuples, or a change from using pairs to some other data structure.

Now, I would actually support the idea of having a type class for categories with such a diagonal map. But this already exists:

http://hackage.haskell.org/package/categories-1.0.7/docs/Control-Category-Ca... -- See 'diag'.

One thing I think would be really nice is for the proc/do (Arrow) notation to be defined in terms of the stuff which is currently in the 'categories' package, which ultimately might mean blessing that stuff a little more. Of course, Conal has also experimented with interpreting lambdas in terms of similar classes of operations, which is an extremely powerful idea as well.

On Wed, 24 Jul 2019 at 09:54, Vladislav Zavialov wrote:

...

map (\x->(x,x)) is quite a punctuation soup compared to ‘map dup’.

- Vlad

...

On 24 Jul 2019, at 16:48, Cale Gibbard wrote:

Does lambda not exist for a reason? _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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