Use traverse instead of mapM all over the place

Cabal/Distribution/Compat/Binary/Class.hs

@@ -36,8 +36,9 @@ import Foreign
 import Data.ByteString.Lazy (ByteString)
 import qualified Data.ByteString.Lazy as L
 
-import Data.Char    (chr,ord)
-import Data.List    (unfoldr)
+import Data.Char     (chr,ord)
+import Data.List     (unfoldr)
+import Data.Foldable (traverse_)
 
 -- And needed for the instances:
 import qualified Data.ByteString as B
@@ -389,7 +390,7 @@ instance (Binary a, Binary b, Binary c, Binary d, Binary e,
 -- Container types
 
 instance Binary a => Binary [a] where
-    put l  = put (length l) >> mapM_ put l
+    put l  = put (length l) >> traverse_ put l
     get    = do n <- get :: Get Int
                 getMany n
 
@@ -444,26 +445,26 @@ instance Binary ByteString where
 -- Maps and Sets
 
 instance (Binary a) => Binary (Set.Set a) where
-    put s = put (Set.size s) >> mapM_ put (Set.toAscList s)
+    put s = put (Set.size s) >> traverse_ put (Set.toAscList s)
     get   = liftM Set.fromDistinctAscList get
 
 instance (Binary k, Binary e) => Binary (Map.Map k e) where
-    put m = put (Map.size m) >> mapM_ put (Map.toAscList m)
+    put m = put (Map.size m) >> traverse_ put (Map.toAscList m)
     get   = liftM Map.fromDistinctAscList get
 
 instance Binary IntSet.IntSet where
-    put s = put (IntSet.size s) >> mapM_ put (IntSet.toAscList s)
+    put s = put (IntSet.size s) >> traverse_ put (IntSet.toAscList s)
     get   = liftM IntSet.fromDistinctAscList get
 
 instance (Binary e) => Binary (IntMap.IntMap e) where
-    put m = put (IntMap.size m) >> mapM_ put (IntMap.toAscList m)
+    put m = put (IntMap.size m) >> traverse_ put (IntMap.toAscList m)
     get   = liftM IntMap.fromDistinctAscList get
 
 ------------------------------------------------------------------------
 -- Queues and Sequences
 
 instance (Binary e) => Binary (Seq.Seq e) where
-    put s = put (Seq.length s) >> Fold.mapM_ put s
+    put s = put (Seq.length s) >> Fold.traverse_ put s
     get = do n <- get :: Get Int
              rep Seq.empty n get
       where rep xs 0 _ = return $! xs
@@ -496,7 +497,7 @@ instance (Binary i, Ix i, Binary e) => Binary (Array i e) where
     put a = do
         put (bounds a)
         put (rangeSize $ bounds a) -- write the length
-        mapM_ put (elems a)        -- now the elems.
+        traverse_ put (elems a)        -- now the elems.
     get = do
         bs <- get
         n  <- get                  -- read the length
@@ -510,7 +511,7 @@ instance (Binary i, Ix i, Binary e, IArray UArray e) => Binary (UArray i e) wher
     put a = do
         put (bounds a)
         put (rangeSize $ bounds a) -- now write the length
-        mapM_ put (elems a)
+        traverse_ put (elems a)
     get = do
         bs <- get
         n  <- get

Cabal/Distribution/Compat/Graph.hs

@@ -293,7 +293,7 @@ revNeighbors g k = do
 -- Requires amortized construction of graph.
 closure :: Graph a -> [Key a] -> Maybe [a]
 closure g ks = do
-    vs <- mapM (graphKeyToVertex g) ks
+    vs <- traverse (graphKeyToVertex g) ks
     return (decodeVertexForest g (G.dfs (graphForward g) vs))
 
 -- | Compute the reverse closure of a graph from some set
@@ -302,7 +302,7 @@ closure g ks = do
 -- Requires amortized construction of graph.
 revClosure :: Graph a -> [Key a] -> Maybe [a]
 revClosure g ks = do
-    vs <- mapM (graphKeyToVertex g) ks
+    vs <- traverse (graphKeyToVertex g) ks
     return (decodeVertexForest g (G.dfs (graphAdjoint g) vs))
 
 flattenForest :: Tree.Forest a -> [a]

Cabal/Distribution/PackageDescription/Check.hs

@@ -49,6 +49,7 @@ import Distribution.Text
 import Distribution.Simple.LocalBuildInfo hiding (compiler)
 import Language.Haskell.Extension
 
+import Control.Monad (mapM)
 import Data.List  (group)
 import qualified System.Directory as System
          ( doesFileExist, doesDirectoryExist )

Cabal/Distribution/PackageDescription/Parse.hs

@@ -534,7 +534,7 @@ readAndParseFile withFileContents' parser verbosity fpath = do
         let (line, message) = locatedErrorMsg e
         dieWithLocation fpath line message
     ParseOk warnings x -> do
-        mapM_ (warn verbosity . showPWarning fpath) $ reverse warnings
+        traverse_ (warn verbosity . showPWarning fpath) $ reverse warnings
         return x
 
 readHookedBuildInfo :: Verbosity -> FilePath -> IO HookedBuildInfo
@@ -561,15 +561,15 @@ isStanzaHeader _ = False
 
 mapSimpleFields :: (Field -> ParseResult Field) -> [Field]
                 -> ParseResult [Field]
-mapSimpleFields f = mapM walk
+mapSimpleFields f = traverse walk
   where
     walk fld@F{} = f fld
     walk (IfBlock l c fs1 fs2) = do
-      fs1' <- mapM walk fs1
-      fs2' <- mapM walk fs2
+      fs1' <- traverse walk fs1
+      fs2' <- traverse walk fs2
       return (IfBlock l c fs1' fs2')
     walk (Section ln n l fs1) = do
-      fs1' <-  mapM walk fs1
+      fs1' <-  traverse walk fs1
       return (Section ln n l fs1')
 
 -- prop_isMapM fs = mapSimpleFields return fs == return fs
@@ -1053,7 +1053,7 @@ parsePackageDescription file = do
             condFlds = [ f | f@IfBlock{} <- allflds ]
             sections = [ s | s@Section{} <- allflds ]
 
-        mapM_
+        traverse_
             (\(Section l n _ _) -> lift . warning $
                 "Unexpected section '" ++ n ++ "' on line " ++ show l)
             sections
@@ -1073,11 +1073,11 @@ parsePackageDescription file = do
         -- to check the CondTree, rather than grovel everywhere
         -- inside the conditional bits).
         deps <- liftM concat
-              . mapM (lift . parseConstraint)
+              . traverse (lift . parseConstraint)
               . filter isConstraint
               $ simplFlds
 
-        ifs <- mapM processIfs condFlds
+        ifs <- traverse processIfs condFlds
 
         return (CondNode a deps ifs)
       where
@@ -1123,10 +1123,10 @@ parsePackageDescription file = do
         PM ()
     checkForUndefinedFlags flags mlib sub_libs exes tests = do
         let definedFlags = map flagName flags
-        mapM_ (checkCondTreeFlags definedFlags) (maybeToList mlib)
-        mapM_ (checkCondTreeFlags definedFlags . snd) sub_libs
-        mapM_ (checkCondTreeFlags definedFlags . snd) exes
-        mapM_ (checkCondTreeFlags definedFlags . snd) tests
+        traverse_ (checkCondTreeFlags definedFlags) (maybeToList mlib)
+        traverse_ (checkCondTreeFlags definedFlags . snd) sub_libs
+        traverse_ (checkCondTreeFlags definedFlags . snd) exes
+        traverse_ (checkCondTreeFlags definedFlags . snd) tests
 
     checkCondTreeFlags :: [FlagName] -> CondTree ConfVar c a -> PM ()
     checkCondTreeFlags definedFlags ct = do

Cabal/Distribution/ParseUtils.hs

@@ -387,14 +387,14 @@ fName _ = error "fname: not a field or section"
 
 readFields :: String -> ParseResult [Field]
 readFields input = ifelse
-               =<< mapM (mkField 0)
+               =<< traverse (mkField 0)
                =<< mkTree tokens
 
   where ls = (lines . normaliseLineEndings) input
         tokens = (concatMap tokeniseLine . trimLines) ls
 
 readFieldsFlat :: String -> ParseResult [Field]
-readFieldsFlat input = mapM (mkField 0)
+readFieldsFlat input = traverse (mkField 0)
                    =<< mkTree tokens
   where ls = (lines . normaliseLineEndings) input
         tokens = (concatMap tokeniseLineFlat . trimLines) ls
@@ -568,7 +568,7 @@ mkField d (Node (n,_,l) ts) = case span (\c -> isAlphaNum c || c == '-') l of
                         then tabsError n
                         else return $ F n (map toLower name)
                                           (fieldValue rest' followingLines)
-    rest'       -> do ts' <- mapM (mkField (d+1)) ts
+    rest'       -> do ts' <- traverse (mkField (d+1)) ts
                       return (Section n (map toLower name) rest' ts')
  where    fieldValue firstLine followingLines =
             let firstLine' = trimLeading firstLine

Cabal/Distribution/Simple.hs

@@ -505,7 +505,7 @@ clean pkg_descr flags = do
       when exists (removeDirectoryRecursive distPref)
 
     -- Any extra files the user wants to remove
-    mapM_ removeFileOrDirectory (extraTmpFiles pkg_descr)
+    traverse_ removeFileOrDirectory (extraTmpFiles pkg_descr)
 
     -- If the user wanted to save the config, write it back
     traverse_ (writePersistBuildConfig distPref) maybeConfig

Cabal/Distribution/Simple/Bench.hs

@@ -96,7 +96,7 @@ bench args pkg_descr lbi flags = do
 
     let totalBenchmarks = length bmsToRun
     notice verbosity $ "Running " ++ show totalBenchmarks ++ " benchmarks..."
-    exitcodes <- mapM doBench bmsToRun
+    exitcodes <- traverse doBench bmsToRun
     let allOk = totalBenchmarks == length (filter (== ExitSuccess) exitcodes)
     unless allOk exitFailure
   where

Cabal/Distribution/Simple/BuildTarget.hs

@@ -139,7 +139,7 @@ readBuildTargets pkg targetStrs = do
     let (uproblems, utargets) = readUserBuildTargets targetStrs
     reportUserBuildTargetProblems uproblems
 
-    utargets' <- mapM checkTargetExistsAsFile utargets
+    utargets' <- traverse checkTargetExistsAsFile utargets
 
     let (bproblems, btargets) = resolveBuildTargets pkg utargets'
     reportBuildTargetProblems bproblems

Cabal/Distribution/Simple/Compiler.hs

@@ -197,7 +197,7 @@ registrationPackageDB dbs = last dbs
 
 
 absolutePackageDBPaths :: PackageDBStack -> IO PackageDBStack
-absolutePackageDBPaths = mapM absolutePackageDBPath
+absolutePackageDBPaths = traverse absolutePackageDBPath
 
 absolutePackageDBPath :: PackageDB -> IO PackageDB
 absolutePackageDBPath GlobalPackageDB        = return GlobalPackageDB

Cabal/Distribution/Simple/Configure.hs

@@ -1345,12 +1345,12 @@ configurePkgconfigPackages verbosity pkg_descr conf
     (_, _, conf') <- requireProgramVersion
                        (lessVerbose verbosity) pkgConfigProgram
                        (orLaterVersion $ Version [0,9,0] []) conf
-    mapM_ requirePkg allpkgs
-    mlib' <- mapM addPkgConfigBILib (library pkg_descr)
-    libs' <- mapM addPkgConfigBILib (subLibraries pkg_descr)
-    exes' <- mapM addPkgConfigBIExe (executables pkg_descr)
-    tests' <- mapM addPkgConfigBITest (testSuites pkg_descr)
-    benches' <- mapM addPkgConfigBIBench (benchmarks pkg_descr)
+    traverse_ requirePkg allpkgs
+    mlib' <- traverse addPkgConfigBILib (library pkg_descr)
+    libs' <- traverse addPkgConfigBILib (subLibraries pkg_descr)
+    exes' <- traverse addPkgConfigBIExe (executables pkg_descr)
+    tests' <- traverse addPkgConfigBITest (testSuites pkg_descr)
+    benches' <- traverse addPkgConfigBIBench (benchmarks pkg_descr)
     let pkg_descr' = pkg_descr { library = mlib',
                                  subLibraries = libs', executables = exes',
                                  testSuites = tests', benchmarks = benches' }
@@ -2132,7 +2132,7 @@ checkPackageProblems verbosity gpkg pkg = do
       errors   = [ e | PackageBuildImpossible e <- pureChecks ++ ioChecks ]
       warnings = [ w | PackageBuildWarning    w <- pureChecks ++ ioChecks ]
   if null errors
-    then mapM_ (warn verbosity) warnings
+    then traverse_ (warn verbosity) warnings
     else die (intercalate "\n\n" errors)
 
 -- | Preform checks if a relocatable build is allowed
@@ -2189,11 +2189,11 @@ checkRelocatable verbosity pkg lbi
     -- prefix of the package
     depsPrefixRelative = do
         pkgr <- GHC.pkgRoot verbosity lbi (last (withPackageDB lbi))
-        mapM_ (doCheck pkgr) ipkgs
+        traverse_ (doCheck pkgr) ipkgs
       where
         doCheck pkgr ipkg
           | maybe False (== pkgr) (Installed.pkgRoot ipkg)
-          = mapM_ (\l -> when (isNothing $ stripPrefix p l) (die (msg l)))
+          = traverse_ (\l -> when (isNothing $ stripPrefix p l) (die (msg l)))
                   (Installed.libraryDirs ipkg)
           | otherwise
           = return ()

Cabal/Distribution/Simple/GHC.hs

@@ -203,7 +203,7 @@ guessToolFromGhcPath tool ghcProg verbosity searchpath
        info verbosity $ "looking for tool " ++ toolname
          ++ " near compiler in " ++ given_dir
        debug verbosity $ "candidate locations: " ++ show guesses
-       exists <- mapM doesFileExist guesses
+       exists <- traverse doesFileExist guesses
        case [ file | (file, True) <- zip guesses exists ] of
                    -- If we can't find it near ghc, fall back to the usual
                    -- method.
@@ -397,7 +397,7 @@ getInstalledPackages' :: Verbosity -> [PackageDB] -> ProgramConfiguration
                      -> IO [(PackageDB, [InstalledPackageInfo])]
 getInstalledPackages' verbosity packagedbs conf
   | ghcVersion >= Version [6,9] [] =
-  sequence
+  sequenceA
     [ do pkgs <- HcPkg.dump (hcPkgInfo conf) verbosity packagedb
          return (packagedb, pkgs)
     | packagedb <- packagedbs ]
@@ -415,11 +415,11 @@ getInstalledPackages' verbosity packagedbs conf = do
           (UserPackageDB,  _global:_)      -> return $ Nothing
           (SpecificPackageDB specific, _)  -> return $ Just specific
           _ -> die "cannot read ghc-pkg package listing"
-    pkgFiles' <- mapM dbFile packagedbs
-    sequence [ withFileContents file $ \content -> do
+    pkgFiles' <- traverse dbFile packagedbs
+    sequenceA [ withFileContents file $ \content -> do
                   pkgs <- readPackages file content
                   return (db, pkgs)
-             | (db , Just file) <- zip packagedbs pkgFiles' ]
+              | (db , Just file) <- zip packagedbs pkgFiles' ]
   where
     -- Depending on the version of ghc we use a different type's Read
     -- instance to parse the package file and then convert.
@@ -441,7 +441,7 @@ getInstalledPackagesMonitorFiles :: Verbosity -> Platform
                                  -> [PackageDB]
                                  -> IO [FilePath]
 getInstalledPackagesMonitorFiles verbosity platform progdb =
-    mapM getPackageDBPath
+    traverse getPackageDBPath
   where
     getPackageDBPath :: PackageDB -> IO FilePath
     getPackageDBPath GlobalPackageDB =
@@ -659,17 +659,17 @@ buildOrReplLib forRepl verbosity numJobs pkg_descr lbi lib clbi = do
         libInstallPath = libdir $ absoluteComponentInstallDirs pkg_descr lbi uid NoCopyDest
         sharedLibInstallPath = libInstallPath </> mkSharedLibName compiler_id uid
 
-    stubObjs <- catMaybes <$> sequence
+    stubObjs <- catMaybes <$> sequenceA
       [ findFileWithExtension [objExtension] [libTargetDir]
           (ModuleName.toFilePath x ++"_stub")
       | ghcVersion < Version [7,2] [] -- ghc-7.2+ does not make _stub.o files
       , x <- libModules lib ]
-    stubProfObjs <- catMaybes <$> sequence
+    stubProfObjs <- catMaybes <$> sequenceA
       [ findFileWithExtension ["p_" ++ objExtension] [libTargetDir]
           (ModuleName.toFilePath x ++"_stub")
       | ghcVersion < Version [7,2] [] -- ghc-7.2+ does not make _stub.o files
       , x <- libModules lib ]
-    stubSharedObjs <- catMaybes <$> sequence
+    stubSharedObjs <- catMaybes <$> sequenceA
       [ findFileWithExtension ["dyn_" ++ objExtension] [libTargetDir]
           (ModuleName.toFilePath x ++"_stub")
       | ghcVersion < Version [7,2] [] -- ghc-7.2+ does not make _stub.o files

Cabal/Distribution/Simple/GHC/Internal.hs

@@ -349,7 +349,7 @@ getHaskellObjects _implInfo lib lbi pref wanted_obj_ext allow_split_objs
         let splitSuffix = "_" ++ wanted_obj_ext ++ "_split"
             dirs = [ pref </> (ModuleName.toFilePath x ++ splitSuffix)
                    | x <- libModules lib ]
-        objss <- mapM getDirectoryContents dirs
+        objss <- traverse getDirectoryContents dirs
         let objs = [ dir </> obj
                    | (objs',dir) <- zip objss dirs, obj <- objs',
                      let obj_ext = takeExtension obj,

Cabal/Distribution/Simple/GHCJS.hs

@@ -161,7 +161,7 @@ guessToolFromGhcjsPath tool ghcjsProg verbosity searchpath
                                            guessNormal]
        info verbosity $ "looking for tool " ++ toolname
          ++ " near compiler in " ++ dir
-       exists <- mapM doesFileExist guesses
+       exists <- traverse doesFileExist guesses
        case [ file | (file, True) <- zip guesses exists ] of
                    -- If we can't find it near ghc, fall back to the usual
                    -- method.
@@ -228,7 +228,7 @@ checkPackageDbStack _ =
 getInstalledPackages' :: Verbosity -> [PackageDB] -> ProgramConfiguration
                       -> IO [(PackageDB, [InstalledPackageInfo])]
 getInstalledPackages' verbosity packagedbs conf =
-  sequence
+  sequenceA
     [ do pkgs <- HcPkg.dump (hcPkgInfo conf) verbosity packagedb
          return (packagedb, pkgs)
     | packagedb <- packagedbs ]

Cabal/Distribution/Simple/Haddock.hs

@@ -569,7 +569,7 @@ haddockPackagePaths :: [InstalledPackageInfo]
                     -> Maybe (InstalledPackageInfo -> FilePath)
                     -> IO ([(FilePath, Maybe FilePath)], Maybe String)
 haddockPackagePaths ipkgs mkHtmlPath = do
-  interfaces <- sequence
+  interfaces <- sequenceA
     [ case interfaceAndHtmlPath ipkg of
         Nothing -> return (Left (packageId ipkg))
         Just (interface, html) -> do
@@ -750,7 +750,7 @@ getExeSourceFiles lbi exe clbi = do
 getSourceFiles :: [FilePath]
                   -> [ModuleName.ModuleName]
                   -> IO [(ModuleName.ModuleName, FilePath)]
-getSourceFiles dirs modules = flip mapM modules $ \m -> fmap ((,) m) $
+getSourceFiles dirs modules = flip traverse modules $ \m -> fmap ((,) m) $
     findFileWithExtension ["hs", "lhs"] dirs (ModuleName.toFilePath m)
       >>= maybe (notFound m) (return . normalise)
   where

Cabal/Distribution/Simple/Hpc.hs

@@ -124,7 +124,7 @@ markupPackage :: Verbosity
               -> IO ()
 markupPackage verbosity lbi distPref libName suites = do
     let tixFiles = map (tixFilePath distPref way . testName) suites
-    tixFilesExist <- mapM doesFileExist tixFiles
+    tixFilesExist <- traverse doesFileExist tixFiles
     when (and tixFilesExist) $ do
         -- behaviour of 'markup' depends on version, so we need *a* version
         -- but no particular one