[GHC] #13572: Add ArgMin / ArgMax pattern synonyms

[GHC]

#13572: Add ArgMin / ArgMax pattern synonyms
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by Iceland_jack:

@@ -20,1 +20,1 @@
- pattern ArgMax [maxArg, maxValue} = Max (Arg maxArg maxValue)
+ pattern ArgMax {maxArg, maxValue} = Max (Arg maxArg maxValue)

New description:

 {{{#!hs
 import Data.Semigroup

 pattern ArgMin :: a -> b -> ArgMin a b
 pattern ArgMin a b = Min (Arg a b)

 pattern ArgMax :: a -> b -> ArgMax a b
 pattern ArgMax a b = Max (Arg a b)
 }}}

 Or even record pattern synonyms, à la
 [https://github.com/energyflowanalysis/efa-2.1/blob/3eb86c0b6b2d2fb66cd5b76ce5c0437d42f8cdf8/sandbox/delaunay/HalfPlaneMap.hs#L181
 this]

 {{{#!hs
 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)
 }}}

 and we can define

 {{{#!hs
 import Data.Semigroup.Foldable

 argmin :: Ord k => Foldable1 f => (a -> k) -> (f a -> a)
 argmin f = minValue . foldMap1 (\a -> ArgMin (f a) a)

 argmax :: Ord k => Foldable1 f => (a -> k) -> (f a -> a)
 argmax f = maxValue . foldMap1 (\a -> ArgMax (f a) a)
 }}}

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13572#comment:1>
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