Follow hlint suggestion: use void

.hlint.yaml

@@ -1,34 +1,33 @@
 # Warnings currently triggered by your code
 - ignore: {name: "Avoid NonEmpty.unzip"} # 1 hint
-- ignore: {name: "Avoid lambda"} # 49 hints
-- ignore: {name: "Eta reduce"} # 139 hints
+- ignore: {name: "Avoid lambda"} # 54 hints
+- ignore: {name: "Eta reduce"} # 136 hints
 - ignore: {name: "Hoist not"} # 16 hints
 - ignore: {name: "Move filter"} # 4 hints
-- ignore: {name: "Redundant $!"} # 1 hint
-- ignore: {name: "Redundant bracket"} # 273 hints
+- ignore: {name: "Redundant $!"} # 3 hints
+- ignore: {name: "Redundant bracket"} # 253 hints
 - ignore: {name: "Redundant guard"} # 1 hint
 - ignore: {name: "Redundant if"} # 6 hints
 - ignore: {name: "Redundant lambda"} # 16 hints
 - ignore: {name: "Redundant multi-way if"} # 1 hint
-- ignore: {name: "Redundant return"} # 9 hints
+- ignore: {name: "Redundant return"} # 7 hints
 - ignore: {name: "Use $>"} # 5 hints
 - ignore: {name: "Use ++"} # 4 hints
-- ignore: {name: "Use :"} # 29 hints
+- ignore: {name: "Use :"} # 30 hints
 - ignore: {name: "Use <$"} # 2 hints
-- ignore: {name: "Use <$>"} # 82 hints
+- ignore: {name: "Use <$>"} # 83 hints
 - ignore: {name: "Use <&>"} # 16 hints
 - ignore: {name: "Use <=<"} # 4 hints
 - ignore: {name: "Use =<<"} # 7 hints
 - ignore: {name: "Use >=>"} # 3 hints
 - ignore: {name: "Use Down"} # 3 hints
 - ignore: {name: "Use bimap"} # 7 hints
-- ignore: {name: "Use camelCase"} # 97 hints
+- ignore: {name: "Use camelCase"} # 96 hints
 - ignore: {name: "Use const"} # 36 hints
 - ignore: {name: "Use fst"} # 2 hints
-- ignore: {name: "Use newtype instead of data"} # 31 hints
+- ignore: {name: "Use newtype instead of data"} # 32 hints
 - ignore: {name: "Use null"} # 2 hints
-- ignore: {name: "Use record patterns"} # 16 hints
-- ignore: {name: "Use void"} # 23 hints
+- ignore: {name: "Use record patterns"} # 15 hints
 
 - ignore: {name: "Functor law", within: [Test.Laws]}
 - ignore: {name: "Monoid law, left identity", within: [Test.Laws, UnitTests.Distribution.Utils.NubList]}

Cabal-syntax/src/Distribution/Compat/Parsing.hs

@@ -82,7 +82,7 @@ option x p = p <|> pure x
 -- It only fails if @p@ fails after consuming input. It discards the result
 -- of @p@. (Plays the role of parsec's optional, which conflicts with Applicative's optional)
 skipOptional :: Alternative m => m a -> m ()
-skipOptional p = (() <$ p) <|> pure ()
+skipOptional p = void p <|> pure ()
 {-# INLINE skipOptional #-}
 
 -- | @between open close p@ parses @open@, followed by @p@ and @close@.
@@ -224,7 +224,7 @@ class Alternative m => Parsing m where
   -- | A version of many that discards its input. Specialized because it
   -- can often be implemented more cheaply.
   skipMany :: m a -> m ()
-  skipMany p = () <$ many p
+  skipMany p = void $ many p
   {-# INLINE skipMany #-}
 
   -- | @skipSome p@ applies the parser @p@ /one/ or more times, skipping

Cabal/src/Distribution/Backpack/ReadyComponent.hs

@@ -403,11 +403,9 @@ toReadyComponents pid_map subst0 comps =
       -- Top-level instantiation per subst0
       | not (Map.null subst0)
       , [lc] <- filter lc_public (Map.elems cmap) =
-          do
-            _ <- instantiateUnitId (lc_cid lc) subst0
-            return ()
+          void $ instantiateUnitId (lc_cid lc) subst0
       | otherwise =
           forM_ (Map.elems cmap) $ \lc ->
             if null (lc_insts lc)
-              then instantiateUnitId (lc_cid lc) Map.empty >> return ()
-              else indefiniteUnitId (lc_cid lc) >> return ()
+              then void $ instantiateUnitId (lc_cid lc) Map.empty
+              else void $ indefiniteUnitId (lc_cid lc)

Cabal/src/Distribution/Simple/Glob/Internal.hs

@@ -79,7 +79,7 @@ instance Parsec Glob where
     where
       dirSep :: CabalParsing m => m ()
       dirSep =
-        () <$ P.char '/'
+        void (P.char '/')
           <|> P.try
             ( do
                 _ <- P.char '\\'

cabal-install/src/Distribution/Client/ProjectBuilding/PackageFileMonitor.hs

@@ -151,9 +151,7 @@ checkPackageFileMonitorChanged
         pkgconfig
     case configChanged of
       MonitorChanged monitorReason ->
-        return (Left (BuildStatusConfigure monitorReason'))
-        where
-          monitorReason' = fmap (const ()) monitorReason
+        return (Left (BuildStatusConfigure $ void monitorReason))
       MonitorUnchanged () _
         -- The configChanged here includes the identity of the dependencies,
         -- so depsBuildStatus is just needed for the changes in the content
@@ -182,16 +180,14 @@ checkPackageFileMonitorChanged
               (MonitorChanged monitorReason, _) ->
                 return (Left (BuildStatusBuild mreg buildReason))
                 where
-                  buildReason = BuildReasonFilesChanged monitorReason'
-                  monitorReason' = fmap (const ()) monitorReason
+                  buildReason = BuildReasonFilesChanged $ void monitorReason
               (MonitorUnchanged _ _, MonitorChanged monitorReason) ->
                 -- this should only happen if the file is corrupt or been
                 -- manually deleted. We don't want to bother with another
                 -- phase just for this, so we'll reregister by doing a build.
                 return (Left (BuildStatusBuild Nothing buildReason))
                 where
-                  buildReason = BuildReasonFilesChanged monitorReason'
-                  monitorReason' = fmap (const ()) monitorReason
+                  buildReason = BuildReasonFilesChanged $ void monitorReason
               (MonitorUnchanged _ _, MonitorUnchanged _ _)
                 | pkgHasEphemeralBuildTargets pkg ->
                     return (Left (BuildStatusBuild mreg buildReason))

cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs

@@ -1329,8 +1329,8 @@ parsePackageLocationTokenQ =
       where
         outerTerm = alternateEither1 outerToken (braces innerTerm)
         innerTerm = alternateEither innerToken (braces innerTerm)
-        outerToken = Parse.munch1 outerChar >> return ()
-        innerToken = Parse.munch1 innerChar >> return ()
+        outerToken = void $ Parse.munch1 outerChar
+        innerToken = void $ Parse.munch1 innerChar
         outerChar c = not (isSpace c || c == '{' || c == '}' || c == ',')
         innerChar c = not (isSpace c || c == '{' || c == '}')
         braces = Parse.between (Parse.char '{') (Parse.char '}')

cabal-install/src/Distribution/Client/ProjectOrchestration.hs

@@ -1018,7 +1018,7 @@ selectBuildableTargetsWith' p =
   (fmap . map) forgetTargetDetail . unzip . zipBuildableTargetsWith p
 
 forgetTargetDetail :: AvailableTarget k -> AvailableTarget ()
-forgetTargetDetail = fmap (const ())
+forgetTargetDetail = void
 
 forgetTargetsDetail :: [AvailableTarget k] -> [AvailableTarget ()]
 forgetTargetsDetail = map forgetTargetDetail

cabal-install/src/Distribution/Client/ProjectPlanning.hs

@@ -3048,15 +3048,11 @@ instantiateInstallPlan storeDirLayout defaultInstallDirs elaboratedShared plan =
 
     ready_map = execState work Map.empty
 
-    work = for_ pkgs $ \pkg ->
-      case pkg of
-        InstallPlan.Configured elab
-          | not (Map.null (elabLinkedInstantiatedWith elab)) ->
-              indefiniteUnitId (elabComponentId elab)
-                >> return ()
-        _ ->
-          instantiateUnitId (getComponentId pkg) Map.empty
-            >> return ()
+    work = for_ pkgs $ \case
+      InstallPlan.Configured elab
+        | not (Map.null (elabLinkedInstantiatedWith elab)) ->
+            void $ indefiniteUnitId (elabComponentId elab)
+      pkg -> void $ instantiateUnitId (getComponentId pkg) Map.empty
 
 ---------------------------
 -- Build targets

cabal-testsuite/PackageTests/ExternalCommand/cabal.test.hs

@@ -3,6 +3,7 @@ import qualified System.Process as Process
 import Control.Concurrent (threadDelay)
 import System.Directory (removeFile)
 import Control.Exception (catch, throwIO)
+import Control.Monad (void)
 import System.IO.Error (isDoesNotExistError)
 import qualified Data.Time.Clock as Time
 import qualified Data.Time.Format as Time
@@ -16,18 +17,18 @@ main = do
     exe_path <- withPlan $ planExePath "setup-test" "cabal-aaaa"
     addToPath (takeDirectory exe_path) $ do
       -- Test that the thing works at all
-      res <- cabal_raw_action ["aaaa"] (\h -> () <$ Process.waitForProcess h)
+      res <- cabal_raw_action ["aaaa"] (\h -> void (Process.waitForProcess h))
 
       -- Test that the extra arguments are passed on
-      res <- cabal_raw_action ["aaaa", "--foobaz"] (\h -> () <$ Process.waitForProcess h)
+      res <- cabal_raw_action ["aaaa", "--foobaz"] (\h -> void (Process.waitForProcess h))
       assertOutputContains "--foobaz" res
 
       -- Test what happens with "global" flags
-      res <- cabal_raw_action ["aaaa", "--version"] (\h -> () <$ Process.waitForProcess h)
+      res <- cabal_raw_action ["aaaa", "--version"] (\h -> void (Process.waitForProcess h))
       assertOutputContains "--version" res
 
       -- Test what happens with "global" flags
-      res <- cabal_raw_action ["aaaa", "--config-file", "abc"] (\h -> () <$ Process.waitForProcess h)
+      res <- cabal_raw_action ["aaaa", "--config-file", "abc"] (\h -> void (Process.waitForProcess h))
       assertOutputContains "--config-file" res
 
 

cabal-testsuite/PackageTests/ExternalCommandEnv/cabal.test.hs

@@ -3,6 +3,7 @@ import qualified System.Process as Process
 import Control.Concurrent (threadDelay)
 import System.Directory (removeFile)
 import Control.Exception (catch, throwIO)
+import Control.Monad (void)
 import System.IO.Error (isDoesNotExistError)
 import qualified Data.Time.Clock as Time
 import qualified Data.Time.Format as Time
@@ -16,7 +17,7 @@ main =
     env <- getTestEnv
     let new_env = (("OTHER_VAR", Just "is set") : (testEnvironment env))
     withEnv new_env $ addToPath (takeDirectory exe_path) $ do
-      res <- cabal_raw_action ["aaaa"] (\h -> () <$ Process.waitForProcess h)
+      res <- cabal_raw_action ["aaaa"] (\h -> void (Process.waitForProcess h))
       assertOutputContains "cabal-install" res
       assertOutputContains "is set" res
 

cabal-testsuite/PackageTests/ExternalCommandExitCode/cabal.test.hs

@@ -3,6 +3,7 @@ import qualified System.Process as Process
 import Control.Concurrent (threadDelay)
 import System.Directory (removeFile)
 import Control.Exception (catch, throwIO)
+import Control.Monad (void)
 import System.IO.Error (isDoesNotExistError)
 import qualified Data.Time.Clock as Time
 import qualified Data.Time.Format as Time
@@ -17,7 +18,7 @@ main = do
     exe_path <- withPlan $ planExePath "setup-test" "cabal-aaaa"
     addToPath (takeDirectory exe_path) $ do
       -- Test that the thing works at all
-      res <- fails $ cabal_raw_action ["aaaa"] (\h -> () <$ Process.waitForProcess h)
+      res <- fails $ cabal_raw_action ["aaaa"] (\h -> void (Process.waitForProcess h))
       -- Check the exit code is the one returned by subcommand
       unless (resultExitCode res == ExitFailure 99) (assertFailure $ "Incorrect exit code: " ++ show (resultExitCode res))
 

cabal-testsuite/PackageTests/ExternalCommandHelp/cabal.test.hs

@@ -3,6 +3,7 @@ import qualified System.Process as Process
 import Control.Concurrent (threadDelay)
 import System.Directory (removeFile)
 import Control.Exception (catch, throwIO)
+import Control.Monad (void)
 import System.IO.Error (isDoesNotExistError)
 import qualified Data.Time.Clock as Time
 import qualified Data.Time.Format as Time
@@ -14,7 +15,7 @@ main = do
     res <- cabalWithStdin "v2-build" ["all"] ""
     exe_path <- withPlan $ planExePath "setup-test" "cabal-aaaa"
     addToPath (takeDirectory exe_path) $ do
-      res <- cabal_raw_action ["help", "aaaa"] (\h -> () <$ Process.waitForProcess h)
+      res <- cabal_raw_action ["help", "aaaa"] (\h -> void (Process.waitForProcess h))
       assertOutputContains "I am helping with the aaaa command" res