Add Arg{Min,Max} pattern synonyms to Data.Semigroup - Libraries - Haskell.org

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Add Arg{Min,Max} pattern synonyms to Data.Semigroup

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Baldur Blöndal

13 Apr 2017 13 Apr '17

7:22 p.m.

Add (explicitly-bidirectional record) pattern synonyms to Data.Semigroup: pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin {minArg, minValue} = Min (Arg minArg minValue) pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax {maxArg, maxValue} = Max (Arg maxArg maxValue) As described in https://ghc.haskell.org/trac/ghc/ticket/13572

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Edward Kmett

18 Apr 18 Apr

12:52 p.m.

I'm personally weakly +1 on this. It makes the combination of Arg and Max much more convenient to use and points directly to how to use it without code duplication. The potential downside is using a big scary extension in what will become a fairly mainstream module in 8.4, but I think we can phrase our way around the issue when it comes to the libraries part of Haskell-Prime. This opens the door to possibly being smarter about the existing Data.Monoid.First (and Last), encoding them as pattern synonyms for Maybe (Data.Semigroup.First a) (or Last) as well, but we'd likely need to give that a lot more thought / testing. -Edward On Thu, Apr 13, 2017 at 3:22 PM, Baldur Blöndal wrote:

Add (explicitly-bidirectional record) pattern synonyms to Data.Semigroup:

pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin {minArg, minValue} = Min (Arg minArg minValue)

pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax {maxArg, maxValue} = Max (Arg maxArg maxValue)

As described in https://ghc.haskell.org/trac/ghc/ticket/13572

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Ivan Lazar Miljenovic

9:51 p.m.

On 18 April 2017 at 22:52, Edward Kmett wrote:

I'm personally weakly +1 on this. It makes the combination of Arg and Max much more convenient to use and points directly to how to use it without code duplication. The potential downside is using a big scary extension in what will become a fairly mainstream module in 8.4, but I think we can phrase our way around the issue when it comes to the libraries part of Haskell-Prime.

This opens the door to possibly being smarter about the existing Data.Monoid.First (and Last), encoding them as pattern synonyms for Maybe (Data.Semigroup.First a) (or Last) as well, but we'd likely need to give that a lot more thought / testing.

I've actually been considering that recently. I'm weakly +1 on this proposal as well.

-Edward

On Thu, Apr 13, 2017 at 3:22 PM, Baldur Blöndal wrote:

...
Add (explicitly-bidirectional record) pattern synonyms to Data.Semigroup:

pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin {minArg, minValue} = Min (Arg minArg minValue)

pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax {maxArg, maxValue} = Max (Arg maxArg maxValue)

As described in https://ghc.haskell.org/trac/ghc/ticket/13572

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com

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Baldur Blöndal

10:07 p.m.

This opens the door to possibly being smarter about the existing Data.Monoid.First (and Last), encoding them as pattern synonyms for Maybe (Data.Semigroup.First a) (or Last) as well, but we'd likely need to give that a lot more thought / testing.

The potential downside is using a big scary extension in what will become a fairly mainstream module in 8.4, but I think we can phrase our way around

Yes First/Last is a good use for pattern synonyms the issue when it comes to the libraries part of Haskell-Prime. As for this proposal I am in no hurry to see it implemented, I figured pattern synonyms would take time to get adopted to base. What do you mean by "phrase our way" around the issue? (The pattern synonyms could be added to the documentation. . "If you are okay with PatternSynonyms..")

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Mario Blažević

21 Apr 21 Apr

9:42 p.m.

On 2017-04-18 08:52 AM, Edward Kmett wrote:

I'm personally weakly +1 on this. It makes the combination of Arg and Max much more convenient to use and points directly to how to use it without code duplication. The potential downside is using a big scary extension in what will become a fairly mainstream module in 8.4, but I think we can phrase our way around the issue when it comes to the libraries part of Haskell-Prime.

I'm (-1) until I'm convinced that the phrasing-around approach works. Can you spell it out?

This opens the door to possibly being smarter about the existing Data.Monoid.First (and Last), encoding them as pattern synonyms for Maybe (Data.Semigroup.First a) (or Last) as well, but we'd likely need to give that a lot more thought / testing.

-Edward

On Thu, Apr 13, 2017 at 3:22 PM, Baldur Blöndal mailto:baldurpet@gmail.com> wrote:

Add (explicitly-bidirectional record) pattern synonyms to Data.Semigroup:

pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin {minArg, minValue} = Min (Arg minArg minValue)

pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax {maxArg, maxValue} = Max (Arg maxArg maxValue)

As described in https://ghc.haskell.org/trac/ghc/ticket/13572 https://ghc.haskell.org/trac/ghc/ticket/13572

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participants (4)

Baldur Blöndal
Edward Kmett
Ivan Lazar Miljenovic
Mario Blažević