Avoid Data.List.group; prefer Data.List.NonEmpty.group

This allows to avoid further partiality, e. g., map head . group is
replaced by map NE.head . NE.group, and there are less panic calls.

2 files changed, 9 insertions, 8 deletions

diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index 99826e7144..6cbf4dffb9 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -122,8 +122,9 @@ import qualified Data.ByteString.Char8 as BS
 import Data.Char
 import Data.Function
 import Data.IORef ( IORef, modifyIORef, newIORef, readIORef, writeIORef )
-import Data.List ( elemIndices, find, group, intercalate, intersperse,
+import Data.List ( elemIndices, find, intercalate, intersperse,
                    isPrefixOf, isSuffixOf, nub, partition, sort, sortBy, (\\) )
+import qualified Data.List.NonEmpty as NE
 import qualified Data.Set as S
 import Data.Maybe
 import qualified Data.Map as M
@@ -3699,11 +3700,11 @@ completeSetOptions = wrapCompleter flagWordBreakChars $ \w -> do
   return (filter (w `isPrefixOf`) opts)
     where opts = "args":"prog":"prompt":"prompt-cont":"prompt-function":
                  "prompt-cont-function":"editor":"stop":flagList
-          flagList = map head $ group $ sort allNonDeprecatedFlags
+          flagList = map NE.head $ NE.group $ sort allNonDeprecatedFlags
 
 completeSeti = wrapCompleter flagWordBreakChars $ \w -> do
   return (filter (w `isPrefixOf`) flagList)
-    where flagList = map head $ group $ sort allNonDeprecatedFlags
+    where flagList = map NE.head $ NE.group $ sort allNonDeprecatedFlags
 
 completeShowOptions = wrapCompleter flagWordBreakChars $ \w -> do
   return (filter (w `isPrefixOf`) opts)
diff --git a/ghc/GHCi/UI/Tags.hs b/ghc/GHCi/UI/Tags.hs
index 410b2c5927..f1d55eab15 100644
--- a/ghc/GHCi/UI/Tags.hs
+++ b/ghc/GHCi/UI/Tags.hs
@@ -29,7 +29,8 @@ import GHC.Driver.Env
 
 import Control.Monad
 import Data.Function
-import Data.List (sort, sortBy, groupBy)
+import Data.List (sort, sortOn)
+import qualified Data.List.NonEmpty as NE
 import Data.Maybe
 import Data.Ord
 import GHC.Driver.Phases
@@ -176,14 +177,13 @@ collateAndWriteTags ETags file tagInfos = do -- etags style, Emacs/XEmacs
 
 makeTagGroupsWithSrcInfo :: [TagInfo] -> IO [[TagInfo]]
 makeTagGroupsWithSrcInfo tagInfos = do
-  let groups = groupBy ((==) `on` tagFile) $ sortBy (comparing tagFile) tagInfos
+  let groups = NE.groupAllWith tagFile tagInfos
   mapM addTagSrcInfo groups
 
   where
-    addTagSrcInfo [] = throwGhcException (CmdLineError "empty tag file group??")
-    addTagSrcInfo group@(tagInfo:_) = do
+    addTagSrcInfo group@(tagInfo NE.:| _) = do
       file <- readFile $ tagFile tagInfo
-      let sortedGroup = sortBy (comparing tagLine) group
+      let sortedGroup = sortOn tagLine (NE.toList group)
       return $ perFile sortedGroup 1 0 $ lines file
 
     perFile allTags@(tag:tags) cnt pos allLs@(l:ls)