Reduce use of CPP and some imports via new Prelude module

cabal-install/Distribution/Client/Configure.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Configure
@@ -22,6 +21,9 @@ module Distribution.Client.Configure (
     writeConfigFlagsTo, writeConfigFlags,
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Client.Dependency
 import qualified Distribution.Client.InstallPlan as InstallPlan
 import Distribution.Client.SolverInstallPlan (SolverInstallPlan)
@@ -83,11 +85,6 @@ import Distribution.Verbosity as Verbosity
 import Distribution.Version
          ( Version(..), VersionRange, orLaterVersion )
 
-import Control.Monad (unless)
-#if !MIN_VERSION_base(4,8,0)
-import Data.Monoid (Monoid(..))
-#endif
-import Data.Maybe (isJust, fromMaybe)
 import System.FilePath ( (</>) )
 
 -- | Choose the Cabal version such that the setup scripts compiled against this

cabal-install/Distribution/Client/Exec.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Exec
@@ -12,7 +11,8 @@
 module Distribution.Client.Exec ( exec
                                 ) where
 
-import Control.Monad (unless)
+import Prelude ()
+import Distribution.Client.Compat.Prelude
 
 import qualified Distribution.Simple.GHC   as GHC
 import qualified Distribution.Simple.GHCJS as GHCJS
@@ -34,10 +34,6 @@ import Distribution.Verbosity (Verbosity)
 
 import System.Directory ( doesDirectoryExist )
 import System.FilePath (searchPathSeparator, (</>))
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative ((<$>))
-import Data.Monoid (mempty)
-#endif
 
 
 -- | Execute the given command in the package's environment.

cabal-install/Distribution/Client/FileMonitor.hs

@@ -35,23 +35,18 @@ module Distribution.Client.FileMonitor (
   beginUpdateFileMonitor,
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
 
 #if MIN_VERSION_containers(0,5,0)
-import           Data.Map.Strict (Map)
 import qualified Data.Map.Strict as Map
 #else
-import           Data.Map        (Map)
 import qualified Data.Map        as Map
 #endif
 import qualified Data.ByteString.Lazy as BS
-import           Distribution.Compat.Binary
 import qualified Distribution.Compat.Binary as Binary
 import qualified Data.Hashable as Hashable
-import           Data.List (sort)
 
-#if !MIN_VERSION_base(4,8,0)
-import           Control.Applicative
-#endif
 import           Control.Monad
 import           Control.Monad.Trans (MonadIO, liftIO)
 import           Control.Monad.State (StateT, mapStateT)
@@ -68,8 +63,6 @@ import           Distribution.Client.Utils (mergeBy, MergeResult(..))
 import           System.FilePath
 import           System.Directory
 import           System.IO
-import           GHC.Generics (Generic)
-
 
 ------------------------------------------------------------------------------
 -- Types for specifying files to monitor

cabal-install/Distribution/Client/Freeze.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Freeze
@@ -16,6 +15,9 @@ module Distribution.Client.Freeze (
     freeze, getFreezePkgs
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Client.Config ( SavedConfig(..) )
 import Distribution.Client.Types
 import Distribution.Client.Targets
@@ -58,13 +60,7 @@ import Distribution.Text
 import Distribution.Verbosity
          ( Verbosity )
 
-import Control.Monad
-         ( when )
 import qualified Data.ByteString.Lazy.Char8 as BS.Char8
-#if !MIN_VERSION_base(4,8,0)
-import Data.Monoid
-         ( mempty )
-#endif
 import Data.Version
          ( showVersion )
 import Distribution.Version

cabal-install/Distribution/Client/Get.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Get
@@ -18,6 +17,9 @@ module Distribution.Client.Get (
     get
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude hiding (get)
+
 import Distribution.Package
          ( PackageId, packageId, packageName )
 import Distribution.Simple.Setup
@@ -48,16 +50,8 @@ import Distribution.Solver.Types.SourcePackage
 import Control.Exception
          ( finally )
 import Control.Monad
-         ( filterM, forM_, unless, when )
-import Data.List
-         ( sortBy )
+         ( forM_, mapM_ )
 import qualified Data.Map
-import Data.Maybe
-         ( listToMaybe, mapMaybe )
-#if !MIN_VERSION_base(4,8,0)
-import Data.Monoid
-         ( mempty )
-#endif
 import Data.Ord
          ( comparing )
 import System.Directory

cabal-install/Distribution/Client/Glob.hs

-{-# LANGUAGE CPP, DeriveGeneric #-}
+{-# LANGUAGE DeriveGeneric #-}
 
 --TODO: [code cleanup] plausibly much of this module should be merged with
 -- similar functionality in Cabal.
@@ -15,14 +15,11 @@ module Distribution.Client.Glob
     , getFilePathRootDirectory
     ) where
 
-import           Data.Char (toUpper)
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import           Data.List (stripPrefix)
-#if !MIN_VERSION_base(4,8,0)
-import           Control.Applicative
-#endif
-import           Control.Monad
-import           Distribution.Compat.Binary
-import           GHC.Generics (Generic)
+import           Control.Monad (mapM)
 
 import           Distribution.Text
 import           Distribution.Compat.ReadP (ReadP, (<++), (+++))

cabal-install/Distribution/Client/HttpUtils.hs

-{-# LANGUAGE CPP, BangPatterns #-}
+{-# LANGUAGE BangPatterns #-}
 -----------------------------------------------------------------------------
 -- | Separate module for HTTP actions, using a proxy server if one exists.
 -----------------------------------------------------------------------------
@@ -14,6 +14,9 @@ module Distribution.Client.HttpUtils (
     isOldHackageURI
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Network.HTTP
          ( Request (..), Response (..), RequestMethod (..)
          , Header(..), HeaderName(..), lookupHeader )
@@ -23,21 +26,14 @@ import Network.URI
 import Network.Browser
          ( browse, setOutHandler, setErrHandler, setProxy
          , setAuthorityGen, request, setAllowBasicAuth, setUserAgent )
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative
-#endif
 import qualified Control.Exception as Exception
 import Control.Exception
          ( evaluate )
 import Control.DeepSeq
          ( force )
 import Control.Monad
-         ( when, guard )
+         ( guard )
 import qualified Data.ByteString.Lazy.Char8 as BS
-import Data.List
-         ( isPrefixOf, find, intercalate )
-import Data.Maybe
-         ( listToMaybe, maybeToList, fromMaybe )
 import qualified Paths_cabal_install (version)
 import Distribution.Verbosity (Verbosity)
 import Distribution.Simple.Utils
@@ -52,8 +48,6 @@ import Distribution.System
          ( buildOS, buildArch )
 import Distribution.Text
          ( display )
-import Data.Char
-         ( isSpace )
 import qualified System.FilePath.Posix as FilePath.Posix
          ( splitDirectories )
 import System.FilePath

cabal-install/Distribution/Client/IndexUtils.hs

-{-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE BangPatterns #-}
@@ -37,6 +36,9 @@ module Distribution.Client.IndexUtils (
   BuildTreeRefType(..), refTypeFromTypeCode, typeCodeFromRefType
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import qualified Codec.Archive.Tar       as Tar
 import qualified Codec.Archive.Tar.Entry as Tar
 import qualified Codec.Archive.Tar.Index as Tar
@@ -77,16 +79,7 @@ import           Distribution.Solver.Types.PackageIndex (PackageIndex)
 import qualified Distribution.Solver.Types.PackageIndex as PackageIndex
 import           Distribution.Solver.Types.SourcePackage
 
-import GHC.Generics (Generic)
-
-import Data.Char   (isAlphaNum)
-import Data.Maybe  (mapMaybe, catMaybes, maybeToList, fromMaybe)
-import Data.List   (isPrefixOf)
 import Data.Word
-#if !MIN_VERSION_base(4,8,0)
-import Data.Monoid (Monoid(..))
-import Control.Applicative
-#endif
 import qualified Data.Map as Map
 import Control.DeepSeq
 import Control.Monad

cabal-install/Distribution/Client/Init.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Init
@@ -23,6 +22,9 @@ module Distribution.Client.Init (
 
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude hiding (empty)
+
 import System.IO
   ( hSetBuffering, stdout, BufferMode(..) )
 import System.Directory
@@ -33,23 +35,13 @@ import System.FilePath
 import Data.Time
   ( getCurrentTime, utcToLocalTime, toGregorian, localDay, getCurrentTimeZone )
 
-import Data.Char
-  ( toUpper )
 import Data.List
-  ( intercalate, nub, groupBy, (\\) )
-import Data.Maybe
-  ( fromMaybe, isJust, catMaybes, listToMaybe )
+  ( groupBy, (\\) )
 import Data.Function
   ( on )
 import qualified Data.Map as M
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative
-  ( (<$>) )
-import Data.Traversable
-  ( traverse )
-#endif
 import Control.Monad
-  ( when, unless, (>=>), join, forM_ )
+  ( (>=>), join, forM_, mapM, mapM_ )
 import Control.Arrow
   ( (&&&), (***) )
 
@@ -932,9 +924,9 @@ generateCabalFile fileName c =
                         (True, _, _)      -> (showComment com $$) . ($$ text "")
                         (False, _, _)     -> ($$ text "")
                       $
-                      comment f <> text s <> colon
-                                <> text (replicate (20 - length s) ' ')
-                                <> text (fromMaybe "" . flagToMaybe $ f)
+                      comment f <<>> text s <<>> colon
+                                <<>> text (replicate (20 - length s) ' ')
+                                <<>> text (fromMaybe "" . flagToMaybe $ f)
    comment NoFlag    = text "-- "
    comment (Flag "") = text "-- "
    comment _         = text ""

cabal-install/Distribution/Client/Init/Heuristics.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Init.Heuristics
@@ -20,6 +19,10 @@ module Distribution.Client.Init.Heuristics (
     guessAuthorNameMail,
     knownCategories,
 ) where
+
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Text         (simpleParse)
 import Distribution.Simple.Setup (Flag(..), flagToMaybe)
 import Distribution.ModuleName
@@ -27,8 +30,6 @@ import Distribution.ModuleName
 import qualified Distribution.Package as P
 import qualified Distribution.PackageDescription as PD
     ( category, packageDescription )
-import Distribution.Simple.Utils
-         ( intercalate )
 import Distribution.Client.Utils
          ( tryCanonicalizePath )
 import Language.Haskell.Extension ( Extension )
@@ -39,16 +40,10 @@ import Distribution.Solver.Types.SourcePackage
     ( packageDescription )
 
 import Distribution.Client.Types ( SourcePackageDb(..) )
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative ( pure, (<$>), (<*>) )
-import Data.Monoid         ( mempty, mappend, mconcat )
-#endif
-import Control.Arrow ( first )
-import Control.Monad ( liftM )
-import Data.Char   ( isAlphaNum, isNumber, isUpper, isLower, isSpace )
+import Control.Monad ( mapM )
+import Data.Char   ( isNumber, isLower )
 import Data.Either ( partitionEithers )
-import Data.List   ( isInfixOf, isPrefixOf, isSuffixOf, sortBy )
-import Data.Maybe  ( mapMaybe, catMaybes, maybeToList )
+import Data.List   ( isInfixOf )
 import Data.Ord    ( comparing )
 import qualified Data.Set as Set ( fromList, toList )
 import System.Directory ( getCurrentDirectory, getDirectoryContents,

cabal-install/Distribution/Client/Install.hs

@@ -29,14 +29,13 @@ module Distribution.Client.Install (
     pruneInstallPlan
   ) where
 
-import Data.Foldable
-         ( traverse_ )
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Data.List
-         ( isPrefixOf, nub, sort, (\\), find )
+         ( (\\) )
 import qualified Data.Map as Map
 import qualified Data.Set as S
-import Data.Maybe
-         ( catMaybes, isJust, isNothing, fromMaybe, mapMaybe )
 import Control.Exception as Exception
          ( Exception(toException), bracket, catches
          , Handler(Handler), handleJust, IOException, SomeException )
@@ -48,15 +47,9 @@ import System.Exit
          ( ExitCode(..) )
 import Distribution.Compat.Exception
          ( catchIO, catchExit )
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative
-         ( (<$>) )
-import Data.Traversable
-         ( traverse )
-#endif
 import Control.Exception ( assert )
 import Control.Monad
-         ( filterM, forM_, when, unless )
+         ( forM_, mapM )
 import System.Directory
          ( getTemporaryDirectory, doesDirectoryExist, doesFileExist,
            createDirectoryIfMissing, removeFile, renameDirectory,
@@ -165,7 +158,7 @@ import Distribution.Version
          ( Version, VersionRange, foldVersionRange )
 import Distribution.Simple.Utils as Utils
          ( notice, info, warn, debug, debugNoWrap, die
-         , intercalate, withTempDirectory )
+         , withTempDirectory )
 import Distribution.Client.Utils
          ( determineNumJobs, logDirChange, mergeBy, MergeResult(..)
          , tryCanonicalizePath )

cabal-install/Distribution/Client/ProjectConfig.hs

@@ -43,6 +43,9 @@ module Distribution.Client.ProjectConfig (
     BadPerPackageCompilerPaths(..)
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Client.ProjectConfig.Types
 import Distribution.Client.ProjectConfig.Legacy
 import Distribution.Client.RebuildMonad
@@ -96,21 +99,14 @@ import Distribution.Text
 import Distribution.ParseUtils
          ( ParseResult(..), locatedErrorMsg, showPWarning )
 
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative
-#endif
 import Control.Monad
 import Control.Monad.Trans (liftIO)
 import Control.Exception
-import Data.Typeable
-import Data.List (intercalate)
 import Data.Maybe
 import Data.Either
-import Data.Map (Map)
 import qualified Data.Map as Map
 import Data.Set (Set)
 import qualified Data.Set as Set
-import Distribution.Compat.Semigroup
 import System.FilePath hiding (combine)
 import System.Directory
 import Network.URI (URI(..), URIAuth(..), parseAbsoluteURI)

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

-{-# LANGUAGE CPP, RecordWildCards, NamedFieldPuns, DeriveGeneric #-}
+{-# LANGUAGE RecordWildCards, NamedFieldPuns, DeriveGeneric #-}
 
 -- | Project configuration, implementation in terms of legacy types.
 --
@@ -20,6 +20,9 @@ module Distribution.Client.ProjectConfig.Legacy (
     renderPackageLocationToken,
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Client.ProjectConfig.Types
 import Distribution.Client.Types
          ( RemoteRepo(..), emptyRemoteRepo )
@@ -76,14 +79,7 @@ import Distribution.Simple.Command
          ( CommandUI(commandOptions), ShowOrParseArgs(..)
          , OptionField, option, reqArg' )
 
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative
-#endif
-import Control.Monad
 import qualified Data.Map as Map
-import Data.Char (isSpace)
-import Distribution.Compat.Semigroup
-import GHC.Generics (Generic)
 
 ------------------------------------------------------------------
 -- Representing the project config file in terms of legacy types
@@ -1106,11 +1102,11 @@ packageSpecificOptionsSectionDescr =
 programOptionsFieldDescrs :: (a -> [(String, [String])])
                           -> ([(String, [String])] -> a -> a)
                           -> [FieldDescr a]
-programOptionsFieldDescrs get set =
+programOptionsFieldDescrs get' set =
     commandOptionsToFields
   $ programDbOptions
       defaultProgramDb
-      ParseArgs get set
+      ParseArgs get' set
 
 programOptionsSectionDescr :: SectionDescr LegacyPackageConfig
 programOptionsSectionDescr =
@@ -1169,7 +1165,7 @@ programDbOptions
   -> (flags -> [(String, [String])])
   -> ([(String, [String])] -> (flags -> flags))
   -> [OptionField flags]
-programDbOptions progDb showOrParseArgs get set =
+programDbOptions progDb showOrParseArgs get' set =
   case showOrParseArgs of
     -- we don't want a verbose help text list so we just show a generic one:
     ShowArgs  -> [programOptions  "PROG"]
@@ -1179,7 +1175,7 @@ programDbOptions progDb showOrParseArgs get set =
     programOptions prog =
       option "" [prog ++ "-options"]
         ("give extra options to " ++ prog)
-        get set
+        get' set
         (reqArg' "OPTS" (\args -> [(prog, splitArgs args)])
            (\progArgs -> [ joinsArgs args
                          | (prog', args) <- progArgs, prog==prog' ]))
@@ -1238,11 +1234,11 @@ newLineListField = listFieldWithSep Disp.sep
 -- of parseOptCommaList below
 listFieldWithSep :: ([Doc] -> Doc) -> String -> (a -> Doc) -> ReadP [a] a
                  -> (b -> [a]) -> ([a] -> b -> b) -> FieldDescr b
-listFieldWithSep separator name showF readF get set =
-  liftField get set' $
+listFieldWithSep separator name showF readF get' set =
+  liftField get' set' $
     ParseUtils.field name showF' (parseOptCommaList readF)
   where
-    set' xs b = set (get b ++ xs) b
+    set' xs b = set (get' b ++ xs) b
     showF'    = separator . map showF
 
 --TODO: [code cleanup] local redefinition that should replace the version in

cabal-install/Distribution/Client/ProjectPlanning.hs

@@ -51,6 +51,9 @@ module Distribution.Client.ProjectPlanning (
     createPackageDBIfMissing
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import           Distribution.Client.ProjectPlanning.Types
 import           Distribution.Client.PackageHash
 import           Distribution.Client.RebuildMonad
@@ -114,21 +117,14 @@ import           Distribution.Text
 import qualified Distribution.Compat.Graph as Graph
 import           Distribution.Compat.Graph(IsNode(..))
 
-import           Data.Map (Map)
 import qualified Data.Map as Map
 import           Data.Set (Set)
 import qualified Data.Set as Set
-#if !MIN_VERSION_base(4,8,0)
-import           Control.Applicative
-#endif
 import           Control.Monad
 import           Control.Monad.State as State
 import           Control.Exception
-import           Data.Typeable
-import           Data.List
-import           Data.Maybe
+import           Data.List (groupBy, mapAccumL)
 import           Data.Either
-import           Data.Monoid
 import           Data.Function
 import           System.FilePath
 
@@ -1502,8 +1498,8 @@ elaborateInstallPlan platform compiler compilerprogdb pkgConfigDB
       -- the project config specifies values that apply to packages local to
       -- but by default non-local packages get all default config values
       -- the project, and can specify per-package values for any package,
-      | isLocalToProject pkg = local <> perpkg
-      | otherwise            =          perpkg
+      | isLocalToProject pkg = local `mappend` perpkg
+      | otherwise            =                 perpkg
       where
         local  = f localPackagesConfig
         perpkg = maybe mempty f (Map.lookup (packageName pkg) perPackageConfig)

cabal-install/Distribution/Client/RebuildMonad.hs

-{-# LANGUAGE CPP #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
 -- | An abstraction for re-running actions if values or files have changed.
@@ -47,6 +46,9 @@ module Distribution.Client.RebuildMonad (
     monitorDirectoryStatus,
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Client.FileMonitor
 import Distribution.Client.Glob hiding (matchFileGlob)
 import qualified Distribution.Client.Glob as Glob (matchFileGlob)
@@ -54,12 +56,8 @@ import qualified Distribution.Client.Glob as Glob (matchFileGlob)
 import Distribution.Simple.Utils (debug)
 import Distribution.Verbosity    (Verbosity)
 
-#if !MIN_VERSION_base(4,8,0)
-import Control.Applicative
-#endif
 import Control.Monad.State as State
 import Control.Monad.Reader as Reader
-import Distribution.Compat.Binary     (Binary)
 import System.FilePath (takeFileName)
 import System.Directory
 

cabal-install/Distribution/Client/Run.hs

-{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Distribution.Client.Run
@@ -11,6 +10,9 @@
 module Distribution.Client.Run ( run, splitRunArgs )
        where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Types.TargetInfo     (targetCLBI)
 import Distribution.Types.LocalBuildInfo (componentNameTargets')
 
@@ -35,11 +37,6 @@ import Distribution.Verbosity                (Verbosity)
 
 import qualified Distribution.Simple.GHCJS as GHCJS
 
-#if !MIN_VERSION_base(4,8,0)
-import Data.Functor                          ((<$>))
-#endif
-import Data.List                             (find)
-import Data.Foldable                         (traverse_)
 import System.Directory                      (getCurrentDirectory)
 import Distribution.Compat.Environment       (getEnvironment)
 import System.FilePath                       ((<.>), (</>))

cabal-install/Distribution/Client/Sandbox.hs

-{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 -----------------------------------------------------------------------------
 -- |
@@ -42,6 +41,9 @@ module Distribution.Client.Sandbox (
     getPersistOrConfigCompiler
   ) where
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Distribution.Client.Setup
   ( SandboxFlags(..), ConfigFlags(..), ConfigExFlags(..), InstallFlags(..)
   , GlobalFlags(..), configCompilerAux', configPackageDB'
@@ -92,7 +94,7 @@ import Distribution.Simple.Setup              ( Flag(..), HaddockFlags(..)
 import Distribution.Simple.SrcDist            ( prepareTree )
 import Distribution.Simple.Utils              ( die, debug, notice, info, warn
                                               , debugNoWrap, defaultPackageDesc
-                                              , intercalate, topHandlerWith
+                                              , topHandlerWith
                                               , createDirectoryIfMissingVerbose )
 import Distribution.Package                   ( Package(..) )
 import Distribution.System                    ( Platform )
@@ -111,19 +113,12 @@ import qualified Data.Map                          as M
 import qualified Data.Set                          as S
 import Data.Either                            (partitionEithers)
 import Control.Exception                      ( assert, bracket_ )
-import Control.Monad                          ( forM, liftM, liftM2, unless, when )
+import Control.Monad                          ( forM, mapM, mapM_ )
 import Data.Bits                              ( shiftL, shiftR, xor )
-import Data.Char                              ( ord )
 import Data.IORef                             ( newIORef, writeIORef, readIORef )