Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: 1f9e4f54 by Stephen Morgan at 2025-08-03T15:14:08+10:00 refactor: Modify Data.List.sortOn to use (>) instead of compare. (#26184) This lets a more efficient (>) operation be used if one exists. This is technically a breaking change for malformed Ord instances, where x > y is not equivalent to compare x y == GT. Discussed by the CLC in issue #332: https://github.com/haskell/core-libraries-committee/issues/332 - - - - - 3 changed files: - libraries/base/changelog.md - libraries/base/src/Data/List/NonEmpty.hs - libraries/ghc-internal/src/GHC/Internal/Data/OldList.hs Changes: ===================================== libraries/base/changelog.md ===================================== @@ -3,6 +3,7 @@ ## 4.23.0.0 *TBA* * Add `Data.List.NonEmpty.mapMaybe`. ([CLC proposal #337](https://github.com/haskell/core-libraries-committee/issues/337)) * Fix issues with toRational for types capable to represent infinite and not-a-number values ([CLC proposal #338](https://github.com/haskell/core-libraries-committee/issues/338)) + * Modify the implementation of `Data.List.sortOn` to use `(>)` instead of `compare`. ([CLC proposal #332](https://github.com/haskell/core-libraries-committee/issues/332)) ## 4.22.0.0 *TBA* * Shipped with GHC 9.14.1 ===================================== libraries/base/src/Data/List/NonEmpty.hs ===================================== @@ -268,6 +268,9 @@ sort = lift List.sort -- >>> (sortBy . comparing) fst $ (3, 1) :| [(2, 2), (1, 3)] -- (1,3) :| [(2,2),(3,1)] -- +-- However, 'sortOn' may still be faster for instances with a more efficient +-- implementation of '(>)' than 'compare'. +-- -- 'sortWith' is an alias for `sortBy . comparing`. -- -- @since 4.20.0.0 ===================================== libraries/ghc-internal/src/GHC/Internal/Data/OldList.hs ===================================== @@ -216,7 +216,6 @@ module GHC.Internal.Data.OldList import GHC.Internal.Data.Maybe import GHC.Internal.Data.Bits ( (.&.) ) import GHC.Internal.Unicode ( isSpace ) -import GHC.Internal.Data.Ord ( comparing ) import GHC.Internal.Data.Tuple ( fst, snd ) import GHC.Internal.Num @@ -1862,10 +1861,13 @@ rqpart cmp x (y:ys) rle rgt r = -- >>> (sortBy . comparing) fst [(3, 1), (2, 2), (1, 3)] -- [(1,3),(2,2),(3,1)] -- +-- However, 'sortOn' may still be faster for instances with a more efficient +-- implementation of '(>)' than 'compare'. +-- -- @since base-4.8.0.0 sortOn :: Ord b => (a -> b) -> [a] -> [a] sortOn f = - map snd . sortBy (comparing fst) . map (\x -> let y = f x in y `seq` (y, x)) + map snd . actualSort (\x y -> fst x > fst y) . map (\x -> let y = f x in y `seq` (y, x)) -- | Construct a list from a single element. -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/1f9e4f54c793572d09a7222c57519fdc... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/1f9e4f54c793572d09a7222c57519fdc... You're receiving this email because of your account on gitlab.haskell.org.