diff --git a/.hlint.yaml b/.hlint.yaml
index e5672ae408a..f145067339d 100644
--- a/.hlint.yaml
+++ b/.hlint.yaml
@@ -26,7 +26,6 @@
 - ignore: {name: "Use const"} # 36 hints
 - ignore: {name: "Use fold"} # 1 hint
 - ignore: {name: "Use fst"} # 2 hints
-- ignore: {name: "Use lambda-case"} # 58 hints
 - ignore: {name: "Use newtype instead of data"} # 31 hints
 - ignore: {name: "Use null"} # 2 hints
 - ignore: {name: "Use record patterns"} # 16 hints
diff --git a/Cabal-syntax/src/Distribution/Fields/ConfVar.hs b/Cabal-syntax/src/Distribution/Fields/ConfVar.hs
index e5878db3df7..3507ff8810e 100644
--- a/Cabal-syntax/src/Distribution/Fields/ConfVar.hs
+++ b/Cabal-syntax/src/Distribution/Fields/ConfVar.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
 
 module Distribution.Fields.ConfVar (parseConditionConfVar, parseConditionConfVarFromClause) where
@@ -35,7 +36,7 @@ import qualified Text.Parsec.Pos as P
 
 parseConditionConfVarFromClause :: B8.ByteString -> Either P.ParseError (Condition ConfVar)
 parseConditionConfVarFromClause x =
-  readFields x >>= \r -> case r of
+  readFields x >>= \case
     (Section _ xs _ : _) -> P.runParser (parser <* P.eof) () "<condition>" xs
     _ -> Left $ P.newErrorMessage (P.Message "No fields in clause") (P.initialPos "<condition>")
 
@@ -124,11 +125,11 @@ parser = condOr
           ]
 
     -- Number token can have many dots in it: SecArgNum (Position 65 15) "7.6.1"
-    identBS = tokenPrim $ \t -> case t of
+    identBS = tokenPrim $ \case
       SecArgName _ s -> Just s
       _ -> Nothing
 
-    boolLiteral' = tokenPrim $ \t -> case t of
+    boolLiteral' = tokenPrim $ \case
       SecArgName _ s
         | s == "True" -> Just True
         | s == "true" -> Just True
@@ -137,11 +138,11 @@ parser = condOr
       _ -> Nothing
 
     string :: B8.ByteString -> Parser ()
-    string s = tokenPrim $ \t -> case t of
+    string s = tokenPrim $ \case
       SecArgName _ s' | s == s' -> Just ()
       _ -> Nothing
 
-    oper o = tokenPrim $ \t -> case t of
+    oper o = tokenPrim $ \case
       SecArgOther _ o' | o == o' -> Just ()
       _ -> Nothing
 
diff --git a/Cabal-syntax/src/Distribution/Fields/Parser.hs b/Cabal-syntax/src/Distribution/Fields/Parser.hs
index 8d04dfba260..ac1d5b4534a 100644
--- a/Cabal-syntax/src/Distribution/Fields/Parser.hs
+++ b/Cabal-syntax/src/Distribution/Fields/Parser.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
 
@@ -124,15 +125,15 @@ tokIndent :: Parser Int
 tokColon, tokCloseBrace :: Parser ()
 tokOpenBrace :: Parser Position
 tokFieldLine :: Parser (FieldLine Position)
-tokSym = getTokenWithPos $ \t -> case t of L pos (TokSym x) -> Just (mkName pos x); _ -> Nothing
-tokSym' = getTokenWithPos $ \t -> case t of L pos (TokSym x) -> Just (SecArgName pos x); _ -> Nothing
-tokStr = getTokenWithPos $ \t -> case t of L pos (TokStr x) -> Just (SecArgStr pos x); _ -> Nothing
-tokOther = getTokenWithPos $ \t -> case t of L pos (TokOther x) -> Just (SecArgOther pos x); _ -> Nothing
-tokIndent = getToken $ \t -> case t of Indent x -> Just x; _ -> Nothing
-tokColon = getToken $ \t -> case t of Colon -> Just (); _ -> Nothing
-tokOpenBrace = getTokenWithPos $ \t -> case t of L pos OpenBrace -> Just pos; _ -> Nothing
-tokCloseBrace = getToken $ \t -> case t of CloseBrace -> Just (); _ -> Nothing
-tokFieldLine = getTokenWithPos $ \t -> case t of L pos (TokFieldLine s) -> Just (FieldLine pos s); _ -> Nothing
+tokSym = getTokenWithPos $ \case L pos (TokSym x) -> Just (mkName pos x); _ -> Nothing
+tokSym' = getTokenWithPos $ \case L pos (TokSym x) -> Just (SecArgName pos x); _ -> Nothing
+tokStr = getTokenWithPos $ \case L pos (TokStr x) -> Just (SecArgStr pos x); _ -> Nothing
+tokOther = getTokenWithPos $ \case L pos (TokOther x) -> Just (SecArgOther pos x); _ -> Nothing
+tokIndent = getToken $ \case Indent x -> Just x; _ -> Nothing
+tokColon = getToken $ \case Colon -> Just (); _ -> Nothing
+tokOpenBrace = getTokenWithPos $ \case L pos OpenBrace -> Just pos; _ -> Nothing
+tokCloseBrace = getToken $ \case CloseBrace -> Just (); _ -> Nothing
+tokFieldLine = getTokenWithPos $ \case L pos (TokFieldLine s) -> Just (FieldLine pos s); _ -> Nothing
 
 colon, openBrace, closeBrace :: Parser ()
 sectionArg :: Parser (SectionArg Position)
diff --git a/Cabal-syntax/src/Distribution/Types/VersionRange/Internal.hs b/Cabal-syntax/src/Distribution/Types/VersionRange/Internal.hs
index cd3082fc7ce..be58ba04ca1 100644
--- a/Cabal-syntax/src/Distribution/Types/VersionRange/Internal.hs
+++ b/Cabal-syntax/src/Distribution/Types/VersionRange/Internal.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DeriveTraversable #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE ScopedTypeVariables #-}
@@ -560,7 +561,7 @@ versionRangeParser digitParser csv = expr
 --
 -- @since 2.2
 majorUpperBound :: Version -> Version
-majorUpperBound = alterVersion $ \numbers -> case numbers of
+majorUpperBound = alterVersion $ \case
   [] -> [0, 1] -- should not happen
   [m1] -> [m1, 1] -- e.g. version '1'
   (m1 : m2 : _) -> [m1, m2 + 1]
diff --git a/Cabal/src/Distribution/PackageDescription/Check/Target.hs b/Cabal/src/Distribution/PackageDescription/Check/Target.hs
index ada37c48b22..bf6bd80dd01 100644
--- a/Cabal/src/Distribution/PackageDescription/Check/Target.hs
+++ b/Cabal/src/Distribution/PackageDescription/Check/Target.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE LambdaCase #-}
+
 -- |
 -- Module      :  Distribution.PackageDescription.Check.Target
 -- Copyright   :  Lennart Kolmodin 2008, Francesco Ariis 2023
@@ -953,7 +955,7 @@ checkGHCOptions title t opts = do
         )
         (PackageDistInexcusable . DynamicUnneeded)
       checkFlagsP
-        ( \opt -> case opt of
+        ( \case
             "-j" -> True
             ('-' : 'j' : d : _) -> isDigit d
             _ -> False
diff --git a/Cabal/src/Distribution/Simple/Build.hs b/Cabal/src/Distribution/Simple/Build.hs
index 7f8b9f0f069..e79a1924eb9 100644
--- a/Cabal/src/Distribution/Simple/Build.hs
+++ b/Cabal/src/Distribution/Simple/Build.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DuplicateRecordFields #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TupleSections #-}
 
@@ -367,7 +368,7 @@ repl_setupHooks
         verbosity = mkVerbosity verbHandles $ fromFlag (replVerbosity flags)
 
     target <-
-      readTargetInfos verbosity pkg_descr lbi args >>= \r -> case r of
+      readTargetInfos verbosity pkg_descr lbi args >>= \case
         -- This seems DEEPLY questionable.
         [] -> case allTargetsInBuildOrder' pkg_descr lbi of
           (target : _) -> return target
diff --git a/Cabal/src/Distribution/Simple/GHC.hs b/Cabal/src/Distribution/Simple/GHC.hs
index 68e6d0be374..51eda011e42 100644
--- a/Cabal/src/Distribution/Simple/GHC.hs
+++ b/Cabal/src/Distribution/Simple/GHC.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RankNTypes #-}
@@ -955,7 +956,7 @@ installLib verbosity lbi targetDir dynlibTargetDir bytecodeTargetDir _builtDir p
   info verbosity ("Wanted install ways: " ++ show libWays)
 
   -- copy .hi files over:
-  forM_ (wantedLibWays isIndef) $ \w -> case w of
+  forM_ (wantedLibWays isIndef) $ \case
     StaticWay -> copyModuleFiles (Suffix "hi")
     DynWay -> copyModuleFiles (Suffix "dyn_hi")
     ProfWay -> copyModuleFiles (Suffix "p_hi")
@@ -970,7 +971,7 @@ installLib verbosity lbi targetDir dynlibTargetDir bytecodeTargetDir _builtDir p
     -- without stripping; see doc/internal/bytecode-libraries.md.
     whenBytecodeLib $ installOrdinaryNoStrip builtDir bytecodeTargetDir bytecodeLibName
 
-    forM_ libWays $ \w -> case w of
+    forM_ libWays $ \case
       StaticWay -> do
         sequence_
           [ installOrdinary
diff --git a/Cabal/src/Distribution/Simple/Haddock.hs b/Cabal/src/Distribution/Simple/Haddock.hs
index d22645d5970..3333fccad3f 100644
--- a/Cabal/src/Distribution/Simple/Haddock.hs
+++ b/Cabal/src/Distribution/Simple/Haddock.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DuplicateRecordFields #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
@@ -1256,7 +1257,7 @@ renderPureArgs version comp platform args =
     , bool [] ["--gen-index"] . fromFlagOrDefault False . argGenIndex $ args
     , maybe [] ((: []) . ("--base-url=" ++)) . flagToMaybe . argBaseUrl $ args
     , bool [verbosityFlag] [] . getAny . argVerbose $ args
-    , map (\o -> case o of Hoogle -> "--hoogle"; Html -> "--html")
+    , map (\case Hoogle -> "--hoogle"; Html -> "--html")
         . fromFlagOrDefault []
         . argOutput
         $ args
diff --git a/Cabal/src/Distribution/Simple/Setup/Config.hs b/Cabal/src/Distribution/Simple/Setup/Config.hs
index 0d1803c2a56..92fb879df9a 100644
--- a/Cabal/src/Distribution/Simple/Setup/Config.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Config.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ViewPatterns #-}
@@ -572,7 +573,7 @@ configureOptions showOrParseArgs =
           [ optArgDef'
               "n"
               (show NoOptimisation, Flag . flagToOptimisationLevel)
-              ( \f -> case f of
+              ( \case
                   Flag NoOptimisation -> []
                   Flag NormalOptimisation -> [Nothing]
                   Flag MaximumOptimisation -> [Just "2"]
@@ -594,7 +595,7 @@ configureOptions showOrParseArgs =
           [ optArg'
               "n"
               (Flag . flagToDebugInfoLevel)
-              ( \f -> case f of
+              ( \case
                   Flag NoDebugInfo -> []
                   Flag MinimalDebugInfo -> [Just "1"]
                   Flag NormalDebugInfo -> [Nothing]
diff --git a/Cabal/src/Distribution/Simple/Setup/Copy.hs b/Cabal/src/Distribution/Simple/Setup/Copy.hs
index a0655de8fc1..5c17607c90b 100644
--- a/Cabal/src/Distribution/Simple/Setup/Copy.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Copy.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ViewPatterns #-}
@@ -117,7 +118,7 @@ copyCommand =
           , "COMPONENTS [FLAGS]"
           ]
     , commandDefaultFlags = defaultCopyFlags
-    , commandOptions = \showOrParseArgs -> case showOrParseArgs of
+    , commandOptions = \case
         ShowArgs ->
           filter
             ( (`notElem` ["target-package-db"])
@@ -145,7 +146,7 @@ copyOptions showOrParseArgs =
         ( reqArg
             "DIR"
             (succeedReadE (Flag . CopyTo))
-            (\f -> case f of Flag (CopyTo p) -> [p]; _ -> [])
+            (\case Flag (CopyTo p) -> [p]; _ -> [])
         )
     , option
         ""
@@ -160,7 +161,7 @@ copyOptions showOrParseArgs =
         ( reqArg
             "DATABASE"
             (succeedReadE (Flag . CopyToDb))
-            (\f -> case f of Flag (CopyToDb p) -> [p]; _ -> [])
+            (\case Flag (CopyToDb p) -> [p]; _ -> [])
         )
     ]
 
diff --git a/Cabal/src/Distribution/Simple/Setup/Install.hs b/Cabal/src/Distribution/Simple/Setup/Install.hs
index 9b03a955ace..b595c7a54df 100644
--- a/Cabal/src/Distribution/Simple/Setup/Install.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Install.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ViewPatterns #-}
@@ -168,7 +169,7 @@ installOptions =
       ( reqArg
           "DATABASE"
           (succeedReadE (Flag . CopyToDb))
-          (\f -> case f of Flag (CopyToDb p) -> [p]; _ -> [])
+          (\case Flag (CopyToDb p) -> [p]; _ -> [])
       )
   ]
 
diff --git a/Cabal/src/Distribution/Utils/UnionFind.hs b/Cabal/src/Distribution/Utils/UnionFind.hs
index b22f07c0e43..29443710ae7 100644
--- a/Cabal/src/Distribution/Utils/UnionFind.hs
+++ b/Cabal/src/Distribution/Utils/UnionFind.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NondecreasingIndentation #-}
 
 -- | A simple mutable union-find data structure.
@@ -50,14 +51,13 @@ fresh desc = do
 -- which points directly to the canonical representation.
 repr :: Point s a -> ST s (Point s a)
 repr point =
-  readPoint point >>= \r ->
-    case r of
-      Link point' -> do
-        point'' <- repr point'
-        when (point'' /= point') $ do
-          writePoint point =<< readPoint point'
-        return point''
-      Info _ _ -> return point
+  readPoint point >>= \case
+    Link point' -> do
+      point'' <- repr point'
+      when (point'' /= point') $ do
+        writePoint point =<< readPoint point'
+      return point''
+    Info _ _ -> return point
 
 -- | Return the canonical element of an equivalence
 -- class 'Point'.
@@ -65,14 +65,12 @@ find :: Point s a -> ST s a
 find point =
   -- Optimize length 0 and 1 case at expense of
   -- general case
-  readPoint point >>= \r ->
-    case r of
-      Info _ d_ref -> readSTRef d_ref
-      Link point' ->
-        readPoint point' >>= \r' ->
-          case r' of
-            Info _ d_ref -> readSTRef d_ref
-            Link _ -> repr point >>= find
+  readPoint point >>= \case
+    Info _ d_ref -> readSTRef d_ref
+    Link point' ->
+      readPoint point' >>= \case
+        Info _ d_ref -> readSTRef d_ref
+        Link _ -> repr point >>= find
 
 -- | Unify two equivalence classes, so that they share
 -- a canonical element. Keeps the descriptor of point2.
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs b/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs
index e551aa2916b..a6e65f24030 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE TupleSections #-}
+{-# LANGUAGE LambdaCase #-}
 
 -- | Fine-grained package dependencies
 --
@@ -184,9 +185,10 @@ nonSetupDeps = select (/= ComponentSetup)
 -- | Library dependencies proper only.  (Includes dependencies
 -- of internal libraries.)
 libraryDeps :: Monoid a => ComponentDeps a -> a
-libraryDeps = select (\c -> case c of ComponentSubLib _ -> True
-                                      ComponentLib -> True
-                                      _ -> False)
+libraryDeps = select (\case
+  ComponentSubLib _ -> True
+  ComponentLib -> True
+  _ -> False)
 
 -- | List components
 components :: ComponentDeps a -> Set Component
diff --git a/cabal-install/src/Distribution/Client/CmdHaddockProject.hs b/cabal-install/src/Distribution/Client/CmdHaddockProject.hs
index 247eb3e2bd4..224550c3f24 100644
--- a/cabal-install/src/Distribution/Client/CmdHaddockProject.hs
+++ b/cabal-install/src/Distribution/Client/CmdHaddockProject.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE PatternSynonyms #-}
 
 module Distribution.Client.CmdHaddockProject
@@ -215,113 +216,114 @@ haddockProjectAction flags _extraArgs globalFlags = do
       -- Copy haddocks to the destination folder
       --
 
-      packageInfos <- fmap (nub . concat) $ for pkgs $ \pkg ->
-        case pkg of
-          Left package | localStyle -> do
-            let packageName = unPackageName (pkgName $ sourcePackageId package)
-                destDir = outputDir </> packageName
-            fmap catMaybes $ for (haddockInterfaces package) $ \interfacePath -> do
-              let docDir = takeDirectory interfacePath
-              a <- doesFileExist interfacePath
-              case a of
-                True -> do
-                  copyDirectoryRecursive verbosity docDir destDir
-                  return $ Just $ Right (packageName, interfacePath, Hidden)
-                False -> return Nothing
-          Left _ -> return []
-          Right package ->
-            case elabLocalToProject package of
-              True -> do
-                let distDirParams = elabDistDirParams sharedConfig' package
-                    pkg_descr = elabPkgDescription package
-
-                    packageName = pkgName $ elabPkgSourceId package
-                    unitId = elabUnitId package
-                    packageDir = haddockDirName ForDevelopment pkg_descr
-                    destDir = outputDir </> packageDir
-                    interfacePath = destDir </> haddockPath pkg_descr
-
-                    buildDir = distBuildDirectory distLayout distDirParams
-                    docDir =
-                      buildDir
-                        </> "doc"
-                        </> "html"
-                        </> packageDir
-
-                a <- doesDirectoryExist docDir
-                if a
-                  then do
-                    copyDirectoryRecursive verbosity docDir destDir
-                    let infos :: [(String, FilePath, Visibility)]
-                        infos =
-                          (unPackageName packageName, interfacePath, Visible)
-                            : [ (sublibDirPath, sublibInterfacePath, Visible)
-                              | lib <- subLibraries pkg_descr
-                              , let sublibDirPath = haddockLibraryDirPath ForDevelopment pkg_descr lib
-                                    sublibInterfacePath =
-                                      outputDir
-                                        </> sublibDirPath
-                                        </> haddockLibraryPath pkg_descr lib
-                              ]
-                            ++ [ (testPath, testInterfacePath, Visible)
-                               | test <- testSuites pkg_descr
-                               , let testPath = haddockTestDirPath ForDevelopment pkg_descr test
-                                     testInterfacePath =
-                                      outputDir
-                                        </> testPath
-                                        </> haddockPath pkg_descr
-                               ]
-                            ++ [ (benchPath, benchInterfacePath, Visible)
-                               | bench <- benchmarks pkg_descr
-                               , let benchPath = haddockBenchmarkDirPath ForDevelopment pkg_descr bench
-                                     benchInterfacePath =
-                                      outputDir
-                                        </> benchPath
-                                        </> haddockPath pkg_descr
-                               ]
-                    infos' <-
-                      mapM
-                        ( \x@(_, path, _) -> do
-                            e <- doesFileExist path
-                            return $
-                              if e
-                                then Right x
-                                else Left path
-                        )
-                        infos
-                    return infos'
-                  else do
-                    warn
-                      verbosity
-                      ( "haddocks of "
-                          ++ unUnitId unitId
-                          ++ " not found in the store"
-                      )
-                    return []
-              False
-                | not localStyle ->
-                    return []
-              False -> do
-                let pkg_descr = elabPkgDescription package
-                    unitId = unUnitId (elabUnitId package)
-                    packageDir =
-                      storePackageDirectory
-                        (cabalStoreDirLayout cabalLayout)
-                        (pkgConfigCompiler sharedConfig')
-                        (elabUnitId package)
-                    -- TODO: use `InstallDirTemplates`
-                    docDir = packageDir </> "share" </> "doc" </> "html"
-                    destDir = outputDir </> haddockDirName ForDevelopment pkg_descr
-                    interfacePath = destDir </> haddockPath pkg_descr
-                a <- doesDirectoryExist docDir
+      packageInfos <- fmap (nub . concat) $
+        for pkgs $
+          \case
+            Left package | localStyle -> do
+              let packageName = unPackageName (pkgName $ sourcePackageId package)
+                  destDir = outputDir </> packageName
+              fmap catMaybes $ for (haddockInterfaces package) $ \interfacePath -> do
+                let docDir = takeDirectory interfacePath
+                a <- doesFileExist interfacePath
                 case a of
                   True -> do
                     copyDirectoryRecursive verbosity docDir destDir
-                    -- non local packages will be hidden in haddock's
-                    -- generated contents page
-                    return [Right (unitId, interfacePath, Hidden)]
-                  False -> do
-                    return [Left unitId]
+                    return $ Just $ Right (packageName, interfacePath, Hidden)
+                  False -> return Nothing
+            Left _ -> return []
+            Right package ->
+              case elabLocalToProject package of
+                True -> do
+                  let distDirParams = elabDistDirParams sharedConfig' package
+                      pkg_descr = elabPkgDescription package
+
+                      packageName = pkgName $ elabPkgSourceId package
+                      unitId = elabUnitId package
+                      packageDir = haddockDirName ForDevelopment pkg_descr
+                      destDir = outputDir </> packageDir
+                      interfacePath = destDir </> haddockPath pkg_descr
+
+                      buildDir = distBuildDirectory distLayout distDirParams
+                      docDir =
+                        buildDir
+                          </> "doc"
+                          </> "html"
+                          </> packageDir
+
+                  a <- doesDirectoryExist docDir
+                  if a
+                    then do
+                      copyDirectoryRecursive verbosity docDir destDir
+                      let infos :: [(String, FilePath, Visibility)]
+                          infos =
+                            (unPackageName packageName, interfacePath, Visible)
+                              : [ (sublibDirPath, sublibInterfacePath, Visible)
+                                | lib <- subLibraries pkg_descr
+                                , let sublibDirPath = haddockLibraryDirPath ForDevelopment pkg_descr lib
+                                      sublibInterfacePath =
+                                        outputDir
+                                          </> sublibDirPath
+                                          </> haddockLibraryPath pkg_descr lib
+                                ]
+                              ++ [ (testPath, testInterfacePath, Visible)
+                                 | test <- testSuites pkg_descr
+                                 , let testPath = haddockTestDirPath ForDevelopment pkg_descr test
+                                       testInterfacePath =
+                                        outputDir
+                                          </> testPath
+                                          </> haddockPath pkg_descr
+                                 ]
+                              ++ [ (benchPath, benchInterfacePath, Visible)
+                                 | bench <- benchmarks pkg_descr
+                                 , let benchPath = haddockBenchmarkDirPath ForDevelopment pkg_descr bench
+                                       benchInterfacePath =
+                                        outputDir
+                                          </> benchPath
+                                          </> haddockPath pkg_descr
+                                 ]
+                      infos' <-
+                        mapM
+                          ( \x@(_, path, _) -> do
+                              e <- doesFileExist path
+                              return $
+                                if e
+                                  then Right x
+                                  else Left path
+                          )
+                          infos
+                      return infos'
+                    else do
+                      warn
+                        verbosity
+                        ( "haddocks of "
+                            ++ unUnitId unitId
+                            ++ " not found in the store"
+                        )
+                      return []
+                False
+                  | not localStyle ->
+                      return []
+                False -> do
+                  let pkg_descr = elabPkgDescription package
+                      unitId = unUnitId (elabUnitId package)
+                      packageDir =
+                        storePackageDirectory
+                          (cabalStoreDirLayout cabalLayout)
+                          (pkgConfigCompiler sharedConfig')
+                          (elabUnitId package)
+                      -- TODO: use `InstallDirTemplates`
+                      docDir = packageDir </> "share" </> "doc" </> "html"
+                      destDir = outputDir </> haddockDirName ForDevelopment pkg_descr
+                      interfacePath = destDir </> haddockPath pkg_descr
+                  a <- doesDirectoryExist docDir
+                  case a of
+                    True -> do
+                      copyDirectoryRecursive verbosity docDir destDir
+                      -- non local packages will be hidden in haddock's
+                      -- generated contents page
+                      return [Right (unitId, interfacePath, Hidden)]
+                    False -> do
+                      return [Left unitId]
 
       --
       -- generate index, content, etc.
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index d873908a08a..3ed5162e11c 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE RecordWildCards #-}
 
@@ -523,7 +524,7 @@ depsFromLocalPackages verbosity ctx targetSelectors = do
         selectComponentTargetForOutdated
         (localPackages ctx)
         targetSelectors
-  fmap concat <$> forM (localPackages ctx) $ \pkg -> case pkg of
+  fmap concat <$> forM (localPackages ctx) $ \case
     SpecificSourcePackage pkg' -> do
       -- Find the package in the resolved targets
       let pkgId = packageId pkg'
diff --git a/cabal-install/src/Distribution/Client/Config.hs b/cabal-install/src/Distribution/Client/Config.hs
index b42cfee9916..dd353e422a6 100644
--- a/cabal-install/src/Distribution/Client/Config.hs
+++ b/cabal-install/src/Distribution/Client/Config.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE PatternSynonyms #-}
 
 -----------------------------------------------------------------------------
@@ -1202,7 +1203,7 @@ configFieldDescriptions src =
           $ let name = "optimization"
              in FieldDescr
                   name
-                  ( \f -> case f of
+                  ( \case
                       Flag NoOptimisation -> Disp.text "False"
                       Flag NormalOptimisation -> Disp.text "True"
                       Flag MaximumOptimisation -> Disp.text "2"
@@ -1233,7 +1234,7 @@ configFieldDescriptions src =
           let name = "debug-info"
            in FieldDescr
                 name
-                ( \f -> case f of
+                ( \case
                     Flag NoDebugInfo -> Disp.text "False"
                     Flag MinimalDebugInfo -> Disp.text "1"
                     Flag NormalDebugInfo -> Disp.text "True"
diff --git a/cabal-install/src/Distribution/Client/FileMonitor.hs b/cabal-install/src/Distribution/Client/FileMonitor.hs
index e4fca6481a8..72067a7af6f 100644
--- a/cabal-install/src/Distribution/Client/FileMonitor.hs
+++ b/cabal-install/src/Distribution/Client/FileMonitor.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# OPTIONS_GHC -Wno-orphans #-}
@@ -1181,10 +1182,9 @@ readCacheFileHashes
 readCacheFileHashes monitor =
   handleDoesNotExist Map.empty $
     handleErrorCall Map.empty $
-      withCacheFile monitor $ \res ->
-        case res of
-          Left _ -> return Map.empty
-          Right (msfs, _, _) -> return (mkFileHashCache msfs)
+      withCacheFile monitor $ \case
+        Left _ -> return Map.empty
+        Right (msfs, _, _) -> return (mkFileHashCache msfs)
   where
     mkFileHashCache :: MonitorStateFileSet -> FileHashCache
     mkFileHashCache (MonitorStateFileSet singlePaths globPaths) =
diff --git a/cabal-install/src/Distribution/Client/Main.hs b/cabal-install/src/Distribution/Client/Main.hs
index fc49cb5148d..c2874093e6c 100644
--- a/cabal-install/src/Distribution/Client/Main.hs
+++ b/cabal-install/src/Distribution/Client/Main.hs
@@ -990,7 +990,7 @@ testAction (buildFlags, testFlags) extraArgs globalFlags = do
       mbWorkDir
       distPref
       "test suites"
-      (\c -> case c of LBI.CTest{} -> True; _ -> False)
+      (\case LBI.CTest{} -> True; _ -> False)
 
   let extraArgs'
         | null extraArgs = case names of
@@ -1114,7 +1114,7 @@ benchmarkAction
         mbWorkDir
         distPref
         "benchmarks"
-        (\c -> case c of LBI.CBench{} -> True; _ -> False)
+        (\case LBI.CBench{} -> True; _ -> False)
 
     let extraArgs'
           | null extraArgs = case names of
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index fc4faa6a64a..844eef40179 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -1720,7 +1720,7 @@ legacyPackageConfigFieldDescrs =
         $ let name = "build-info"
            in FieldDescr
                 name
-                ( \f -> case f of
+                ( \case
                     Flag NoDumpBuildInfo -> Disp.text "False"
                     Flag DumpBuildInfo -> Disp.text "True"
                     _ -> Disp.empty
@@ -1748,7 +1748,7 @@ legacyPackageConfigFieldDescrs =
         $ let name = "optimization"
            in FieldDescr
                 name
-                ( \f -> case f of
+                ( \case
                     Flag NoOptimisation -> Disp.text "False"
                     Flag NormalOptimisation -> Disp.text "True"
                     Flag MaximumOptimisation -> Disp.text "2"
@@ -1773,7 +1773,7 @@ legacyPackageConfigFieldDescrs =
         let name = "debug-info"
          in FieldDescr
               name
-              ( \f -> case f of
+              ( \case
                   Flag NoDebugInfo -> Disp.text "False"
                   Flag MinimalDebugInfo -> Disp.text "1"
                   Flag NormalDebugInfo -> Disp.text "True"
diff --git a/cabal-install/src/Distribution/Client/ProjectOrchestration.hs b/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
index 12718e4be5f..7ca6e32bbf3 100644
--- a/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
+++ b/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE RecordWildCards #-}
@@ -470,7 +471,7 @@ runProjectBuildPhase
     where
       previousBuildOutcomes :: BuildStatusMap -> BuildOutcomes
       previousBuildOutcomes =
-        Map.mapMaybe $ \status -> case status of
+        Map.mapMaybe $ \case
           BuildStatusUpToDate buildSuccess -> Just (Right buildSuccess)
           -- TODO: [nice to have] record build failures persistently
           _ -> Nothing
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs b/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
index 8f5f5211ec1..9ad4b3e3fee 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RecordWildCards #-}
 
@@ -665,27 +666,24 @@ postBuildProjectStatus
 
       packagesBuildLocal :: Set UnitId
       packagesBuildLocal =
-        selectPlanPackageIdSet $ \pkg ->
-          case pkg of
-            InstallPlan.PreExisting _ -> False
-            InstallPlan.Installed _ -> False
-            InstallPlan.Configured srcpkg -> elabLocalToProject srcpkg
+        selectPlanPackageIdSet $ \case
+          InstallPlan.PreExisting _ -> False
+          InstallPlan.Installed _ -> False
+          InstallPlan.Configured srcpkg -> elabLocalToProject srcpkg
 
       packagesBuildInplace :: Set UnitId
       packagesBuildInplace =
-        selectPlanPackageIdSet $ \pkg ->
-          case pkg of
-            InstallPlan.PreExisting _ -> False
-            InstallPlan.Installed _ -> False
-            InstallPlan.Configured srcpkg -> isInplaceBuildStyle (elabBuildStyle srcpkg)
+        selectPlanPackageIdSet $ \case
+          InstallPlan.PreExisting _ -> False
+          InstallPlan.Installed _ -> False
+          InstallPlan.Configured srcpkg -> isInplaceBuildStyle (elabBuildStyle srcpkg)
 
       packagesAlreadyInStore :: Set UnitId
       packagesAlreadyInStore =
-        selectPlanPackageIdSet $ \pkg ->
-          case pkg of
-            InstallPlan.PreExisting _ -> True
-            InstallPlan.Installed _ -> True
-            InstallPlan.Configured _ -> False
+        selectPlanPackageIdSet $ \case
+          InstallPlan.PreExisting _ -> True
+          InstallPlan.Installed _ -> True
+          InstallPlan.Configured _ -> False
 
       selectPlanPackageIdSet
         :: ( InstallPlan.GenericPlanPackage InstalledPackageInfo ElaboratedConfiguredPackage
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 5be55634324..b8f1e72f232 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -2257,7 +2257,7 @@ elaborateInstallPlan
             elabStanzasAvailable = stanzas
 
             elabStanzasRequested :: OptionalStanzaMap (Maybe Bool)
-            elabStanzasRequested = optStanzaTabulate $ \o -> case o of
+            elabStanzasRequested = optStanzaTabulate $ \case
               -- NB: even if a package stanza is requested, if the package
               -- doesn't actually have any of that stanza we omit it from
               -- the request, to ensure that we don't decide that this
diff --git a/cabal-install/src/Distribution/Client/RebuildMonad.hs b/cabal-install/src/Distribution/Client/RebuildMonad.hs
index 14e2b4946bb..4bc349741d2 100644
--- a/cabal-install/src/Distribution/Client/RebuildMonad.hs
+++ b/cabal-install/src/Distribution/Client/RebuildMonad.hs
@@ -220,12 +220,11 @@ delayInitSharedResource action = do
   where
     getOrInitResource :: MVar (Maybe a) -> IO a
     getOrInitResource var =
-      modifyMVar var $ \mx ->
-        case mx of
-          Just x -> return (Just x, x)
-          Nothing -> do
-            x <- action
-            return (Just x, x)
+      modifyMVar var $ \case
+        Just x -> return (Just x, x)
+        Nothing -> do
+          x <- action
+          return (Just x, x)
 
 -- | Much like 'delayInitSharedResource' but for a keyed set of resources.
 --
diff --git a/cabal-install/src/Distribution/Client/Setup.hs b/cabal-install/src/Distribution/Client/Setup.hs
index c2651a33331..1688ff1c023 100644
--- a/cabal-install/src/Distribution/Client/Setup.hs
+++ b/cabal-install/src/Distribution/Client/Setup.hs
@@ -2637,7 +2637,7 @@ installOptions showOrParseArgs =
       ( reqArg
           "DATABASE"
           (succeedReadE (Flag . Cabal.CopyToDb))
-          (\f -> case f of Flag (Cabal.CopyToDb p) -> [p]; _ -> [])
+          (\case Flag (Cabal.CopyToDb p) -> [p]; _ -> [])
       )
   ]
     ++ optionSolverFlags
diff --git a/cabal-install/tests/UnitTests/Distribution/Client/ArbitraryInstances.hs b/cabal-install/tests/UnitTests/Distribution/Client/ArbitraryInstances.hs
index 5a8945eafe0..c02afc79fb2 100644
--- a/cabal-install/tests/UnitTests/Distribution/Client/ArbitraryInstances.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Client/ArbitraryInstances.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE LambdaCase #-}
 {-# OPTIONS_GHC -Wno-orphans #-}
 
 module UnitTests.Distribution.Client.ArbitraryInstances
@@ -319,7 +320,7 @@ instance Arbitrary a => Arbitrary (OptionalStanzaMap a) where
   arbitrary = do
     x1 <- arbitrary
     x2 <- arbitrary
-    return $ optStanzaTabulate $ \x -> case x of
+    return $ optStanzaTabulate $ \case
       TestStanzas -> x1
       BenchStanzas -> x2
 
diff --git a/cabal-testsuite/PackageTests/ExtraProgPathGlobal/setup.test.hs b/cabal-testsuite/PackageTests/ExtraProgPathGlobal/setup.test.hs
index 5aba770b18b..df5d5cd74e7 100644
--- a/cabal-testsuite/PackageTests/ExtraProgPathGlobal/setup.test.hs
+++ b/cabal-testsuite/PackageTests/ExtraProgPathGlobal/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -29,7 +30,7 @@ main = cabalTest $ do
       case mb_sh of
           Nothing -> skip "no sh"
           Just sh -> do
-            let escape = concatMap (\c -> case c of '\\' -> "\\\\\\\\"; x -> [x])
+            let escape = concatMap (\case '\\' -> "\\\\\\\\"; x -> [x])
             void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> escape sh <> "/g", escape (scripts </> "pkg-config.shim"), escape (scripts_winpath </> "pkg-config.shim") ]
             void $ shell "sed" [ "-i", "-e", "s/SCRIPTSDIR/" <> escape scripts <> "/g", escape (scripts </> "pkg-config.shim") ]
             void $ shell "sed" [ "-i", "-e", "s/SCRIPTSWINPATHDIR/" <> escape scripts_winpath <> "/g", escape (scripts_winpath </> "pkg-config.shim") ]
diff --git a/cabal-testsuite/PackageTests/ExtraProgPathLocal/setup.test.hs b/cabal-testsuite/PackageTests/ExtraProgPathLocal/setup.test.hs
index 496d5822dd1..ce1c63c2f57 100644
--- a/cabal-testsuite/PackageTests/ExtraProgPathLocal/setup.test.hs
+++ b/cabal-testsuite/PackageTests/ExtraProgPathLocal/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -20,7 +21,7 @@ main = cabalTest $ do
       case mb_sh of
           Nothing -> skip "no sh"
           Just sh -> do
-            let escape = concatMap (\c -> case c of '\\' -> "\\\\\\\\"; x -> [x])
+            let escape = concatMap (\case '\\' -> "\\\\\\\\"; x -> [x])
             void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> escape sh <> "/g", escape (scripts1 </> "alex.shim"), escape (scripts2 </> "alex.shim") ]
             void $ shell "sed" [ "-i", "-e", "s/SCRIPTSDIR/" <> escape scripts1 <> "/g", escape (scripts1 </> "alex.shim") ]
             void $ shell "sed" [ "-i", "-e", "s/SCRIPTS2DIR/" <> escape scripts2 <> "/g", escape (scripts2 </> "alex.shim") ]
diff --git a/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectory/setup.test.hs b/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectory/setup.test.hs
index 805f56abc9c..010176cb8bb 100644
--- a/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectory/setup.test.hs
+++ b/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectory/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -7,7 +8,7 @@ main = setupAndCabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "ghc.shim", "ghc-pkg.shim"]
diff --git a/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryGhcVersion/setup.test.hs b/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryGhcVersion/setup.test.hs
index e60d3685863..736d98b2c30 100644
--- a/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryGhcVersion/setup.test.hs
+++ b/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryGhcVersion/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -7,7 +8,7 @@ main = setupAndCabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "ghc-7.10.shim", "ghc-pkg-ghc-7.10.shim"]
diff --git a/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryVersion/setup.test.hs b/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryVersion/setup.test.hs
index b5f6b4c88d6..688a04a94d6 100644
--- a/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryVersion/setup.test.hs
+++ b/cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryVersion/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -7,7 +8,7 @@ main = setupAndCabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "ghc-7.10.shim", "ghc-pkg-7.10.shim"]
diff --git a/cabal-testsuite/PackageTests/GhcPkgGuess/Symlink/setup.test.hs b/cabal-testsuite/PackageTests/GhcPkgGuess/Symlink/setup.test.hs
index b188acc36d6..d546451e013 100644
--- a/cabal-testsuite/PackageTests/GhcPkgGuess/Symlink/setup.test.hs
+++ b/cabal-testsuite/PackageTests/GhcPkgGuess/Symlink/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -7,7 +8,7 @@ main = setupAndCabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "bin/ghc.shim", "bin/ghc-pkg.shim"]
diff --git a/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkGhcVersion/setup.test.hs b/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkGhcVersion/setup.test.hs
index bf9b16fa195..d65411aa86d 100644
--- a/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkGhcVersion/setup.test.hs
+++ b/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkGhcVersion/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -7,7 +8,7 @@ main = setupAndCabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "bin/ghc-7.10.shim", "bin/ghc-pkg-7.10.shim"]
diff --git a/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkVersion/setup.test.hs b/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkVersion/setup.test.hs
index 2f406ce6226..a37955754a5 100644
--- a/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkVersion/setup.test.hs
+++ b/cabal-testsuite/PackageTests/GhcPkgGuess/SymlinkVersion/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import Test.Cabal.Prelude
 import System.Directory
 
@@ -7,7 +8,7 @@ main = setupAndCabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "bin/ghc-7.10.shim", "bin/ghc-pkg-ghc-7.10.shim"]
diff --git a/cabal-testsuite/PackageTests/PkgConfigParse/setup.test.hs b/cabal-testsuite/PackageTests/PkgConfigParse/setup.test.hs
index edebd2d131c..9dd22bda19b 100644
--- a/cabal-testsuite/PackageTests/PkgConfigParse/setup.test.hs
+++ b/cabal-testsuite/PackageTests/PkgConfigParse/setup.test.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 import System.Directory
 import Test.Cabal.Prelude
 
@@ -8,7 +9,7 @@ main = cabalTest $ do
         case sh of
             Nothing -> skip "no sh"
             Just sh' -> do
-                let sh'' = concatMap (\c -> case c of
+                let sh'' = concatMap (\case
                             '\\' -> "\\\\\\\\"
                             x -> [x]) sh'
                 void $ shell "sed" [ "-i", "-e", "s/FINDSH/" <> sh'' <> "/g", "pkg-config.shim"]
diff --git a/cabal-testsuite/src/Test/Cabal/Server.hs b/cabal-testsuite/src/Test/Cabal/Server.hs
index bb993d99d84..88b86f7f7e6 100644
--- a/cabal-testsuite/src/Test/Cabal/Server.hs
+++ b/cabal-testsuite/src/Test/Cabal/Server.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NondecreasingIndentation #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
@@ -267,8 +268,7 @@ initServer :: Server -> IO Server
 initServer s0 = do
     -- NB: withProcessHandle reads an MVar and is interruptible
 
-    pid <- withProcessHandle (serverProcessHandle s0) $ \ph ->
-              case ph of
+    pid <- withProcessHandle (serverProcessHandle s0) $ \case
 #if mingw32_HOST_OS
                   OpenHandle x   -> fmap show (Win32.getProcessId x)
 #else