#2659: Add sortOn and other *On functions -------------------------------------+--------------------------------- Reporter: twanvl | Owner: Type: proposal | Status: closed Priority: normal | Milestone: Not GHC Component: libraries/base | Version: 6.9 Resolution: wontfix | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | -------------------------------------+--------------------------------- Comment (by Herbert Valerio Riedel ): In [changeset:"44512e3c855d8fb36ab6580f4f97f842ebcf4c6c/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="44512e3c855d8fb36ab6580f4f97f842ebcf4c6c" Add Data.List.sortOn function (re #9004 and #2659) `sortOn` sorts a list by comparing the results of a key function applied to each element. `sortOn f` is equivalent to `sortBy . comparing f`, but has the performance advantage of only evaluating `f` once for each element in the input list. Historical note: This was already proposed in 2008 as part of http://www.haskell.org/pipermail/libraries/2008-October/010797.html It was, however, the recent re-attempt http://www.haskell.org/pipermail/libraries/2014-April/022489.html that let `sortOn` make it into base at last. Maybe the other functions mentioned in #2659 might be worth reconsidering as well. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/2659#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler