Follow hlint suggestion: use lambda-case

.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

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
 

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)

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]

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

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

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

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

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]

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]; _ -> [])
         )
     ]
 

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]; _ -> [])
       )
   ]
 

Cabal/src/Distribution/Utils/UnionFind.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NondecreasingIndentation #-}
 
 -- | A simple mutable union-find data structure.
@@ -50,29 +51,26 @@ 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'.
 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.

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