Prefer #if defined to #ifdef

Our new CPP linter enforces this.

34 files changed, 155 insertions, 155 deletions

diff --git a/libraries/base/Control/Concurrent.hs b/libraries/base/Control/Concurrent.hs
index ada825d0f0..cc39ddeccf 100644
--- a/libraries/base/Control/Concurrent.hs
+++ b/libraries/base/Control/Concurrent.hs
@@ -117,7 +117,7 @@ import System.Posix.Types ( Fd )
 import Foreign.StablePtr
 import Foreign.C.Types
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import Foreign.C
 import System.IO
 import Data.Functor ( void )
@@ -401,7 +401,7 @@ unsafeResult = either Exception.throwIO return
 -- 'GHC.Conc.closeFdWith'.
 threadWaitRead :: Fd -> IO ()
 threadWaitRead fd
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   -- we have no IO manager implementing threadWaitRead on Windows.
   -- fdReady does the right thing, but we have to call it in a
   -- separate thread, otherwise threadWaitRead won't be interruptible,
@@ -426,7 +426,7 @@ threadWaitRead fd
 -- 'GHC.Conc.closeFdWith'.
 threadWaitWrite :: Fd -> IO ()
 threadWaitWrite fd
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   | threaded  = withThread (waitFd fd 1)
   | otherwise = errorWithoutStackTrace "threadWaitWrite requires -threaded on Windows"
 #else
@@ -441,7 +441,7 @@ threadWaitWrite fd
 -- @since 4.7.0.0
 threadWaitReadSTM :: Fd -> IO (STM (), IO ())
 threadWaitReadSTM fd
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   | threaded = do v <- newTVarIO Nothing
                   mask_ $ void $ forkIO $ do result <- try (waitFd fd 0)
                                              atomically (writeTVar v $ Just result)
@@ -465,7 +465,7 @@ threadWaitReadSTM fd
 -- @since 4.7.0.0
 threadWaitWriteSTM :: Fd -> IO (STM (), IO ())
 threadWaitWriteSTM fd
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   | threaded = do v <- newTVarIO Nothing
                   mask_ $ void $ forkIO $ do result <- try (waitFd fd 1)
                                              atomically (writeTVar v $ Just result)
@@ -481,7 +481,7 @@ threadWaitWriteSTM fd
   = GHC.Conc.threadWaitWriteSTM fd
 #endif
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import ccall unsafe "rtsSupportsBoundThreads" threaded :: Bool
 
 withThread :: IO a -> IO a
diff --git a/libraries/base/Data/Bits.hs b/libraries/base/Data/Bits.hs
index 525f098524..d12d6dc4bd 100644
--- a/libraries/base/Data/Bits.hs
+++ b/libraries/base/Data/Bits.hs
@@ -57,7 +57,7 @@ module Data.Bits (
 
 #include "MachDeps.h"
 
-#ifdef MIN_VERSION_integer_gmp
+#if defined(MIN_VERSION_integer_gmp)
 # define HAVE_INTEGER_GMP1 MIN_VERSION_integer_gmp(1,0,0)
 #endif
 
diff --git a/libraries/base/Data/OldList.hs b/libraries/base/Data/OldList.hs
index ec937e729b..bee1b6f98a 100644
--- a/libraries/base/Data/OldList.hs
+++ b/libraries/base/Data/OldList.hs
@@ -276,7 +276,7 @@ findIndex p     = listToMaybe . findIndices p
 -- | The 'findIndices' function extends 'findIndex', by returning the
 -- indices of all elements satisfying the predicate, in ascending order.
 findIndices      :: (a -> Bool) -> [a] -> [Int]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 findIndices p xs = [ i | (x,i) <- zip xs [0..], p x]
 #else
 -- Efficient definition, adapted from Data.Sequence
@@ -346,7 +346,7 @@ nub                     =  nubBy (==)
 -- user-supplied equality predicate instead of the overloaded '=='
 -- function.
 nubBy                   :: (a -> a -> Bool) -> [a] -> [a]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 nubBy eq []             =  []
 nubBy eq (x:xs)         =  x : nubBy eq (filter (\ y -> not (eq x y)) xs)
 #else
@@ -824,7 +824,7 @@ sort :: (Ord a) => [a] -> [a]
 -- | The 'sortBy' function is the non-overloaded version of 'sort'.
 sortBy :: (a -> a -> Ordering) -> [a] -> [a]
 
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 sort = sortBy compare
 sortBy cmp = foldr (insertBy cmp) []
 #else
@@ -1083,7 +1083,7 @@ lines s                 =  cons (case break (== '\n') s of
 -- | 'unlines' is an inverse operation to 'lines'.
 -- It joins lines, after appending a terminating newline to each.
 unlines                 :: [String] -> String
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 unlines                 =  concatMap (++ "\n")
 #else
 -- HBC version (stolen)
@@ -1118,7 +1118,7 @@ wordsFB c n = go
 -- | 'unwords' is an inverse operation to 'words'.
 -- It joins words with separating spaces.
 unwords                 :: [String] -> String
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 unwords []              =  ""
 unwords ws              =  foldr1 (\w s -> w ++ ' ':s) ws
 #else
diff --git a/libraries/base/Data/Semigroup.hs b/libraries/base/Data/Semigroup.hs
index ec68683799..fae207ef97 100644
--- a/libraries/base/Data/Semigroup.hs
+++ b/libraries/base/Data/Semigroup.hs
@@ -85,7 +85,7 @@ import           Data.Monoid         (Alt (..))
 import qualified Data.Monoid         as Monoid
 import           Data.Ord            (Down(..))
 import           Data.Void
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 import           GHC.Event           (Event, Lifetime)
 #endif
 import           GHC.Generics
@@ -725,7 +725,7 @@ instance Semigroup (Proxy s) where
 instance Semigroup a => Semigroup (IO a) where
     (<>) = liftA2 (<>)
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 -- | @since 4.10.0.0
 instance Semigroup Event where
     (<>) = mappend
diff --git a/libraries/base/Foreign/C/String.hs b/libraries/base/Foreign/C/String.hs
index a162460b25..a8eb60c5a3 100644
--- a/libraries/base/Foreign/C/String.hs
+++ b/libraries/base/Foreign/C/String.hs
@@ -420,7 +420,7 @@ wNUL = 0
 cWcharsToChars :: [CWchar] -> [Char]
 charsToCWchars :: [Char] -> [CWchar]
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 
 -- On Windows, wchar_t is 16 bits wide and CWString uses the UTF-16 encoding.
 
diff --git a/libraries/base/GHC/Conc.hs b/libraries/base/GHC/Conc.hs
index 74d14badf6..8c5c1536d9 100644
--- a/libraries/base/GHC/Conc.hs
+++ b/libraries/base/GHC/Conc.hs
@@ -86,7 +86,7 @@ module GHC.Conc
 
         -- * Miscellaneous
         , withMVar
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
         , asyncRead
         , asyncWrite
         , asyncDoProc
@@ -95,14 +95,14 @@ module GHC.Conc
         , asyncWriteBA
 #endif
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
         , Signal, HandlerFun, setHandler, runHandlers
 #endif
 
         , ensureIOManagerIsRunning
         , ioManagerCapabilitiesChanged
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
         , ConsoleEvent(..)
         , win32ConsoleHandler
         , toWin32ConsoleEvent
@@ -116,6 +116,6 @@ module GHC.Conc
 import GHC.Conc.IO
 import GHC.Conc.Sync
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 import GHC.Conc.Signal
 #endif
diff --git a/libraries/base/GHC/Conc/IO.hs b/libraries/base/GHC/Conc/IO.hs
index be773132ee..eb0bffe8b4 100644
--- a/libraries/base/GHC/Conc/IO.hs
+++ b/libraries/base/GHC/Conc/IO.hs
@@ -39,7 +39,7 @@ module GHC.Conc.IO
         , threadWaitWriteSTM
         , closeFdWith
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
         , asyncRead
         , asyncWrite
         , asyncDoProc
@@ -59,7 +59,7 @@ import GHC.Conc.Sync as Sync
 import GHC.Real ( fromIntegral )
 import System.Posix.Types
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import qualified GHC.Conc.Windows as Windows
 import GHC.Conc.Windows (asyncRead, asyncWrite, asyncDoProc, asyncReadBA,
                          asyncWriteBA, ConsoleEvent(..), win32ConsoleHandler,
@@ -69,14 +69,14 @@ import qualified GHC.Event.Thread as Event
 #endif
 
 ensureIOManagerIsRunning :: IO ()
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 ensureIOManagerIsRunning = Event.ensureIOManagerIsRunning
 #else
 ensureIOManagerIsRunning = Windows.ensureIOManagerIsRunning
 #endif
 
 ioManagerCapabilitiesChanged :: IO ()
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 ioManagerCapabilitiesChanged = Event.ioManagerCapabilitiesChanged
 #else
 ioManagerCapabilitiesChanged = return ()
@@ -90,7 +90,7 @@ ioManagerCapabilitiesChanged = return ()
 -- that has been used with 'threadWaitRead', use 'closeFdWith'.
 threadWaitRead :: Fd -> IO ()
 threadWaitRead fd
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
   | threaded  = Event.threadWaitRead fd
 #endif
   | otherwise = IO $ \s ->
@@ -106,7 +106,7 @@ threadWaitRead fd
 -- that has been used with 'threadWaitWrite', use 'closeFdWith'.
 threadWaitWrite :: Fd -> IO ()
 threadWaitWrite fd
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
   | threaded  = Event.threadWaitWrite fd
 #endif
   | otherwise = IO $ \s ->
@@ -120,7 +120,7 @@ threadWaitWrite fd
 -- in the file descriptor.
 threadWaitReadSTM :: Fd -> IO (Sync.STM (), IO ())
 threadWaitReadSTM fd
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
   | threaded  = Event.threadWaitReadSTM fd
 #endif
   | otherwise = do
@@ -139,7 +139,7 @@ threadWaitReadSTM fd
 -- in the file descriptor.
 threadWaitWriteSTM :: Fd -> IO (Sync.STM (), IO ())
 threadWaitWriteSTM fd
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
   | threaded  = Event.threadWaitWriteSTM fd
 #endif
   | otherwise = do
@@ -164,7 +164,7 @@ closeFdWith :: (Fd -> IO ()) -- ^ Low-level action that performs the real close.
             -> Fd            -- ^ File descriptor to close.
             -> IO ()
 closeFdWith close fd
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
   | threaded  = Event.closeFdWith close fd
 #endif
   | otherwise = close fd
@@ -178,7 +178,7 @@ closeFdWith close fd
 --
 threadDelay :: Int -> IO ()
 threadDelay time
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   | threaded  = Windows.threadDelay time
 #else
   | threaded  = Event.threadDelay time
@@ -193,7 +193,7 @@ threadDelay time
 --
 registerDelay :: Int -> IO (TVar Bool)
 registerDelay usecs
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   | threaded = Windows.registerDelay usecs
 #else
   | threaded = Event.registerDelay usecs
diff --git a/libraries/base/GHC/Conc/Windows.hs b/libraries/base/GHC/Conc/Windows.hs
index 4cbb8cadc2..6b87b06fe7 100644
--- a/libraries/base/GHC/Conc/Windows.hs
+++ b/libraries/base/GHC/Conc/Windows.hs
@@ -53,7 +53,7 @@ import GHC.Show (Show)
 import GHC.Word (Word32, Word64)
 import GHC.Windows
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 # if defined(i386_HOST_ARCH)
 #  define WINDOWS_CCONV stdcall
 # elif defined(x86_64_HOST_ARCH)
diff --git a/libraries/base/GHC/Environment.hs b/libraries/base/GHC/Environment.hs
index 97005eb770..a077f6f8c4 100644
--- a/libraries/base/GHC/Environment.hs
+++ b/libraries/base/GHC/Environment.hs
@@ -9,7 +9,7 @@ import Foreign.C
 import GHC.Base
 import GHC.Real ( fromIntegral )
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import GHC.IO (finally)
 import GHC.Windows
 
@@ -30,7 +30,7 @@ import qualified GHC.Foreign as GHC
 -- command line arguments, starting with the program name, and
 -- including those normally eaten by the RTS (+RTS ... -RTS).
 getFullArgs :: IO [String]
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 -- Ignore the arguments to hs_init on Windows for the sake of Unicode compat
 getFullArgs = do
     p_arg_string <- c_GetCommandLine
diff --git a/libraries/base/GHC/Event/KQueue.hsc b/libraries/base/GHC/Event/KQueue.hsc
index a76cc51b52..e9c8419ea7 100644
--- a/libraries/base/GHC/Event/KQueue.hsc
+++ b/libraries/base/GHC/Event/KQueue.hsc
@@ -56,7 +56,7 @@ import Data.Int (Int64)
 -- Handle brokenness on some BSD variants, notably OS X up to at least
 -- 10.6.  If NOTE_EOF isn't available, we have no way to receive a
 -- notification from the kernel when we reach EOF on a plain file.
-#ifndef NOTE_EOF
+#if !defined(NOTE_EOF)
 # define NOTE_EOF 0
 #endif
 
@@ -132,7 +132,7 @@ data Event = KEvent {
     , filter :: {-# UNPACK #-} !Filter
     , flags  :: {-# UNPACK #-} !Flag
     , fflags :: {-# UNPACK #-} !FFlag
-#ifdef netbsd_HOST_OS
+#if defined(netbsd_HOST_OS)
     , data_  :: {-# UNPACK #-} !Int64
 #else
     , data_  :: {-# UNPACK #-} !CIntPtr
diff --git a/libraries/base/GHC/Event/Poll.hsc b/libraries/base/GHC/Event/Poll.hsc
index 5c5ad494ca..74525c6b40 100644
--- a/libraries/base/GHC/Event/Poll.hsc
+++ b/libraries/base/GHC/Event/Poll.hsc
@@ -158,7 +158,7 @@ newtype Event = Event CShort
 
 -- We have to duplicate the whole enum like this in order for the
 -- hsc2hs cross-compilation mode to work
-#ifdef POLLRDHUP
+#if defined(POLLRDHUP)
 #{enum Event, Event
  , pollIn    = POLLIN
  , pollOut   = POLLOUT
diff --git a/libraries/base/GHC/IO/Buffer.hs b/libraries/base/GHC/IO/Buffer.hs
index 50de06e97e..33eee6363d 100644
--- a/libraries/base/GHC/IO/Buffer.hs
+++ b/libraries/base/GHC/IO/Buffer.hs
@@ -101,7 +101,7 @@ readWord8Buf arr ix = withForeignPtr arr $ \p -> peekByteOff p ix
 writeWord8Buf :: RawBuffer Word8 -> Int -> Word8 -> IO ()
 writeWord8Buf arr ix w = withForeignPtr arr $ \p -> pokeByteOff p ix w
 
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
 type CharBufElem = Word16
 #else
 type CharBufElem = Char
@@ -124,7 +124,7 @@ writeCharBuf arr ix c = withForeignPtr arr $ \p -> writeCharBufPtr p ix c
 
 {-# INLINE readCharBufPtr #-}
 readCharBufPtr :: Ptr CharBufElem -> Int -> IO (Char, Int)
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
 readCharBufPtr p ix = do
   c1 <- peekElemOff p ix
   if (c1 < 0xd800 || c1 > 0xdbff)
@@ -138,7 +138,7 @@ readCharBufPtr p ix = do c <- peekElemOff (castPtr p) ix; return (c, ix+1)
 
 {-# INLINE writeCharBufPtr #-}
 writeCharBufPtr :: Ptr CharBufElem -> Int -> Char -> IO Int
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
 writeCharBufPtr p ix ch
   | c < 0x10000 = do pokeElemOff p ix (fromIntegral c)
                      return (ix+1)
@@ -153,7 +153,7 @@ writeCharBufPtr p ix ch = do pokeElemOff (castPtr p) ix ch; return (ix+1)
 #endif
 
 charSize :: Int
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
 charSize = 2
 #else
 charSize = 4
@@ -186,7 +186,7 @@ data Buffer e
         bufR     :: !Int           -- offset of last item + 1
   }
 
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
 type CharBuffer = Buffer Word16
 #else
 type CharBuffer = Buffer Char
@@ -208,7 +208,7 @@ isFullBuffer Buffer{ bufR=w, bufSize=s } = s == w
 
 -- if a Char buffer does not have room for a surrogate pair, it is "full"
 isFullCharBuffer :: Buffer e -> Bool
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
 isFullCharBuffer buf = bufferAvailable buf < 2
 #else
 isFullCharBuffer = isFullBuffer
diff --git a/libraries/base/GHC/IO/Encoding/CodePage.hs b/libraries/base/GHC/IO/Encoding/CodePage.hs
index aea4314742..42980b59bc 100644
--- a/libraries/base/GHC/IO/Encoding/CodePage.hs
+++ b/libraries/base/GHC/IO/Encoding/CodePage.hs
@@ -32,7 +32,7 @@ import GHC.IO.Encoding.UTF8 (mkUTF8)
 import GHC.IO.Encoding.UTF16 (mkUTF16le, mkUTF16be)
 import GHC.IO.Encoding.UTF32 (mkUTF32le, mkUTF32be)
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 # if defined(i386_HOST_ARCH)
 #  define WINDOWS_CCONV stdcall
 # elif defined(x86_64_HOST_ARCH)
diff --git a/libraries/base/GHC/IO/Encoding/CodePage/API.hs b/libraries/base/GHC/IO/Encoding/CodePage/API.hs
index 8cf77b0a96..f1d9d93e8f 100644
--- a/libraries/base/GHC/IO/Encoding/CodePage/API.hs
+++ b/libraries/base/GHC/IO/Encoding/CodePage/API.hs
@@ -157,7 +157,7 @@ newCP rec fn cp = do
 
 utf16_native_encode' :: EncodeBuffer
 utf16_native_decode' :: DecodeBuffer
-#ifdef WORDS_BIGENDIAN
+#if defined(WORDS_BIGENDIAN)
 utf16_native_encode' = utf16be_encode
 utf16_native_decode' = utf16be_decode
 #else
@@ -204,7 +204,7 @@ utf16_native_decode ibuf obuf = do
 
 cpDecode :: Word32 -> Int -> DecodeBuffer
 cpDecode cp max_char_size = \ibuf obuf -> do
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
     let mbuf = obuf
 #else
     -- FIXME: share the buffer between runs, even if the buffer is not the perfect size
@@ -215,7 +215,7 @@ cpDecode cp max_char_size = \ibuf obuf -> do
     debugIO $ "cpDecode " ++ summaryBuffer ibuf ++ " " ++ summaryBuffer mbuf
     (why1, ibuf', mbuf') <- cpRecode try' is_valid_prefix max_char_size 1 0 1 ibuf mbuf
     debugIO $ "cpRecode (cpDecode) = " ++ show why1 ++ " " ++ summaryBuffer ibuf' ++ " " ++ summaryBuffer mbuf'
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
     return (why1, ibuf', mbuf')
 #else
     -- Convert as much UTF-16 as possible to UTF-32. Note that it's impossible for this to fail
@@ -265,7 +265,7 @@ cpDecode cp max_char_size = \ibuf obuf -> do
 
 cpEncode :: Word32 -> Int -> EncodeBuffer
 cpEncode cp _max_char_size = \ibuf obuf -> do
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
     let mbuf' = ibuf
 #else
     -- FIXME: share the buffer between runs, even though that means we can't size the buffer as we want.
@@ -281,7 +281,7 @@ cpEncode cp _max_char_size = \ibuf obuf -> do
     debugIO $ "\ncpEncode " ++ summaryBuffer mbuf' ++ " " ++ summaryBuffer obuf
     (why2, target_utf16_count, mbuf', obuf) <- saner (cpRecode try' is_valid_prefix 2 1 1 0) (mbuf' { bufState = ReadBuffer }) obuf
     debugIO $ "cpRecode (cpEncode) = " ++ show why2 ++ " " ++ summaryBuffer mbuf' ++ " " ++ summaryBuffer obuf
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
     return (why2, mbuf', obuf)
 #else
     case why2 of
diff --git a/libraries/base/GHC/IO/Encoding/Iconv.hs b/libraries/base/GHC/IO/Encoding/Iconv.hs
index 061bd60c20..16354364b4 100644
--- a/libraries/base/GHC/IO/Encoding/Iconv.hs
+++ b/libraries/base/GHC/IO/Encoding/Iconv.hs
@@ -85,7 +85,7 @@ foreign import ccall unsafe "localeEncoding"
     c_localeEncoding :: IO CString
 
 haskellChar :: String
-#ifdef WORDS_BIGENDIAN
+#if defined(WORDS_BIGENDIAN)
 haskellChar | charSize == 2 = "UTF-16BE"
             | otherwise     = "UTF-32BE"
 #else
diff --git a/libraries/base/GHC/IO/FD.hs b/libraries/base/GHC/IO/FD.hs
index c4e4d46c53..8eafe08fdc 100644
--- a/libraries/base/GHC/IO/FD.hs
+++ b/libraries/base/GHC/IO/FD.hs
@@ -43,7 +43,7 @@ import qualified GHC.IO.Device
 import GHC.IO.Device (SeekMode(..), IODeviceType(..))
 import GHC.Conc.IO
 import GHC.IO.Exception
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import GHC.Windows
 #endif
 
@@ -53,7 +53,7 @@ import qualified System.Posix.Internals
 import System.Posix.Internals hiding (FD, setEcho, getEcho)
 import System.Posix.Types
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 # if defined(i386_HOST_ARCH)
 #  define WINDOWS_CCONV stdcall
 # elif defined(x86_64_HOST_ARCH)
@@ -71,7 +71,7 @@ c_DEBUG_DUMP = False
 
 data FD = FD {
   fdFD :: {-# UNPACK #-} !CInt,
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   -- On Windows, a socket file descriptor needs to be read and written
   -- using different functions (send/recv).
   fdIsSocket_ :: {-# UNPACK #-} !Int
@@ -83,7 +83,7 @@ data FD = FD {
 #endif
  }
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 fdIsSocket :: FD -> Bool
 fdIsSocket fd = fdIsSocket_ fd /= 0
 #endif
@@ -167,7 +167,7 @@ openFile filepath iomode non_blocking =
                   ReadWriteMode -> rw_flags
                   AppendMode    -> append_flags
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
       binary_flags = o_BINARY
 #else
       binary_flags = 0
@@ -259,12 +259,12 @@ mkFD fd iomode mb_stat is_socket is_nonblock = do
 
         _other_type -> return ()
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
     when (not is_socket) $ setmode fd True >> return ()
 #endif
 
     return (FD{ fdFD = fd,
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
                 fdIsNonBlocking = fromEnum is_nonblock
 #else
                 fdIsSocket_ = fromEnum is_socket
@@ -273,7 +273,7 @@ mkFD fd iomode mb_stat is_socket is_nonblock = do
             fd_type)
 
 getUniqueFileInfo :: CInt -> CDev -> CIno -> IO (Word64, Word64)
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 getUniqueFileInfo _ dev ino = return (fromIntegral dev, fromIntegral ino)
 #else
 getUniqueFileInfo fd _ _ = do
@@ -283,7 +283,7 @@ getUniqueFileInfo fd _ _ = do
       liftM2 (,) (peek devptr) (peek inoptr)
 #endif
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import ccall unsafe "__hscore_setmode"
   setmode :: CInt -> Bool -> IO CInt
 #endif
@@ -293,7 +293,7 @@ foreign import ccall unsafe "__hscore_setmode"
 
 stdFD :: CInt -> FD
 stdFD fd = FD { fdFD = fd,
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
                 fdIsSocket_ = 0
 #else
                 fdIsNonBlocking = 0
@@ -315,7 +315,7 @@ close :: FD -> IO ()
 close fd =
   do let closer realFd =
            throwErrnoIfMinus1Retry_ "GHC.IO.FD.close" $
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
            if fdIsSocket fd then
              c_closesocket (fromIntegral realFd)
            else
@@ -333,7 +333,7 @@ release :: FD -> IO ()
 release fd = do _ <- unlockFile (fdFD fd)
                 return ()
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import WINDOWS_CCONV unsafe "HsBase.h closesocket"
    c_closesocket :: CInt -> IO CInt
 #endif
@@ -465,7 +465,7 @@ fdWriteNonBlocking fd ptr bytes = do
 
 -- Low level routines for reading/writing to (raw)buffers:
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 
 {-
 NOTE [nonblock]:
@@ -647,7 +647,7 @@ foreign import ccall unsafe "rtsSupportsBoundThreads" threaded :: Bool
 -- -----------------------------------------------------------------------------
 -- utils
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 throwErrnoIfMinus1RetryOnBlock  :: String -> IO CSsize -> IO CSsize -> IO CSsize
 throwErrnoIfMinus1RetryOnBlock loc f on_block  =
   do
@@ -672,7 +672,7 @@ foreign import ccall unsafe "lockFile"
 foreign import ccall unsafe "unlockFile"
   unlockFile :: CInt -> IO CInt
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import ccall unsafe "get_unique_file_info"
   c_getUniqueFileInfo :: CInt -> Ptr Word64 -> Ptr Word64 -> IO ()
 #endif
diff --git a/libraries/base/GHC/IO/Handle.hs b/libraries/base/GHC/IO/Handle.hs
index 256f802c3d..648523a11f 100644
--- a/libraries/base/GHC/IO/Handle.hs
+++ b/libraries/base/GHC/IO/Handle.hs
@@ -232,7 +232,7 @@ hSetBuffering handle mode =
           is_tty <- IODevice.isTerminal haDevice
           when (is_tty && isReadableHandleType haType) $
                 case mode of
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
         -- 'raw' mode under win32 is a bit too specialised (and troublesome
         -- for most common uses), so simply disable its use here.
                   NoBuffering -> IODevice.setRaw haDevice True
diff --git a/libraries/base/GHC/IO/Handle/FD.hs b/libraries/base/GHC/IO/Handle/FD.hs
index e988b25c9f..786fccc4f1 100644
--- a/libraries/base/GHC/IO/Handle/FD.hs
+++ b/libraries/base/GHC/IO/Handle/FD.hs
@@ -91,14 +91,14 @@ stdHandleFinalizer fp m = do
 -- We have to put the FDs into binary mode on Windows to avoid the newline
 -- translation that the CRT IO library does.
 setBinaryMode :: FD.FD -> IO ()
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 setBinaryMode fd = do _ <- setmode (FD.fdFD fd) True
                       return ()
 #else
 setBinaryMode _ = return ()
 #endif
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import ccall unsafe "__hscore_setmode"
   setmode :: CInt -> Bool -> IO CInt
 #endif
@@ -202,7 +202,7 @@ mkHandleFromFD
 
 mkHandleFromFD fd0 fd_type filepath iomode set_non_blocking mb_codec
   = do
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
     -- turn on non-blocking mode
     fd <- if set_non_blocking 
              then FD.setNonBlockingMode fd0 True
diff --git a/libraries/base/GHC/IO/Handle/Text.hs b/libraries/base/GHC/IO/Handle/Text.hs
index 8d927384c8..57b9534976 100644
--- a/libraries/base/GHC/IO/Handle/Text.hs
+++ b/libraries/base/GHC/IO/Handle/Text.hs
@@ -271,7 +271,7 @@ unpack !buf !r !w acc0
               -- Here, we are rather careful to only put an *evaluated* character
               -- in the output string. Due to pointer tagging, this allows the consumer
               -- to avoid ping-ponging between the actual consumer code and the thunk code
-#ifdef CHARBUF_UTF16
+#if defined(CHARBUF_UTF16)
               -- reverse-order decoding of UTF-16
               c2 <- peekElemOff pbuf i
               if (c2 < 0xdc00 || c2 > 0xdffff)
diff --git a/libraries/base/GHC/IO/Handle/Types.hs b/libraries/base/GHC/IO/Handle/Types.hs
index 8f739810c4..c58a9fb1b0 100644
--- a/libraries/base/GHC/IO/Handle/Types.hs
+++ b/libraries/base/GHC/IO/Handle/Types.hs
@@ -46,7 +46,7 @@ import GHC.Read
 import GHC.Word
 import GHC.IO.Device
 import Data.Typeable
-#ifdef DEBUG
+#if defined(DEBUG)
 import Control.Monad
 #endif
 
@@ -179,7 +179,7 @@ isReadWriteHandleType _                 = False
 --   * In a wriite Handle, the Char buffer is always empty (we encode when writing)
 --
 checkHandleInvariants :: Handle__ -> IO ()
-#ifdef DEBUG
+#if defined(DEBUG)
 checkHandleInvariants h_ = do
  bbuf <- readIORef (haByteBuffer h_)
  checkBuffer bbuf
@@ -367,7 +367,7 @@ data NewlineMode
 -- | The native newline representation for the current platform: 'LF'
 -- on Unix systems, 'CRLF' on Windows.
 nativeNewline :: Newline
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 nativeNewline = CRLF
 #else
 nativeNewline = LF
diff --git a/libraries/base/GHC/List.hs b/libraries/base/GHC/List.hs
index 018c0a78d8..70bfbe4de0 100644
--- a/libraries/base/GHC/List.hs
+++ b/libraries/base/GHC/List.hs
@@ -79,7 +79,7 @@ tail []                 =  errorEmptyList "tail"
 
 -- | Extract the last element of a list, which must be finite and non-empty.
 last                    :: [a] -> a
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 last [x]                =  x
 last (_:xs)             =  last xs
 last []                 =  errorEmptyList "last"
@@ -98,7 +98,7 @@ lastError = errorEmptyList "last"
 -- | Return all the elements of a list except the last one.
 -- The list must be non-empty.
 init                    :: [a] -> [a]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 init [x]                =  []
 init (x:xs)             =  x : init xs
 init []                 =  errorEmptyList "init"
@@ -550,7 +550,7 @@ dropWhile p xs@(x:xs')
 -- It is an instance of the more general 'Data.List.genericTake',
 -- in which @n@ may be of any integral type.
 take                   :: Int -> [a] -> [a]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 take n _      | n <= 0 =  []
 take _ []              =  []
 take n (x:xs)          =  x : take (n-1) xs
@@ -617,7 +617,7 @@ takeFB c n x xs
 -- It is an instance of the more general 'Data.List.genericDrop',
 -- in which @n@ may be of any integral type.
 drop                   :: Int -> [a] -> [a]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 drop n xs     | n <= 0 =  xs
 drop _ []              =  []
 drop n (_:xs)          =  drop (n-1) xs
@@ -652,7 +652,7 @@ drop n ls
 -- in which @n@ may be of any integral type.
 splitAt                :: Int -> [a] -> ([a],[a])
 
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 splitAt n xs           =  (take n xs, drop n xs)
 #else
 splitAt n ls
@@ -694,7 +694,7 @@ span p xs@(x:xs')
 -- 'break' @p@ is equivalent to @'span' ('not' . p)@.
 
 break                   :: (a -> Bool) -> [a] -> ([a],[a])
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 break p                 =  span (not . p)
 #else
 -- HBC version (stolen)
@@ -707,7 +707,7 @@ break p xs@(x:xs')
 -- | 'reverse' @xs@ returns the elements of @xs@ in reverse order.
 -- @xs@ must be finite.
 reverse                 :: [a] -> [a]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 reverse                 =  foldl (flip (:)) []
 #else
 reverse l =  rev l []
@@ -720,7 +720,7 @@ reverse l =  rev l []
 -- 'True', the list must be finite; 'False', however, results from a 'False'
 -- value at a finite index of a finite or infinite list.
 and                     :: [Bool] -> Bool
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 and                     =  foldr (&&) True
 #else
 and []          =  True
@@ -737,7 +737,7 @@ and (x:xs)      =  x && and xs
 -- 'False', the list must be finite; 'True', however, results from a 'True'
 -- value at a finite index of a finite or infinite list.
 or                      :: [Bool] -> Bool
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 or                      =  foldr (||) False
 #else
 or []           =  False
@@ -756,7 +756,7 @@ or (x:xs)       =  x || or xs
 -- value for the predicate applied to an element at a finite index of a finite or infinite list.
 any                     :: (a -> Bool) -> [a] -> Bool
 
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 any p                   =  or . map p
 #else
 any _ []        = False
@@ -775,7 +775,7 @@ any p (x:xs)    = p x || any p xs
 -- 'True', the list must be finite; 'False', however, results from a 'False'
 -- value for the predicate applied to an element at a finite index of a finite or infinite list.
 all                     :: (a -> Bool) -> [a] -> Bool
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 all p                   =  and . map p
 #else
 all _ []        =  True
@@ -794,7 +794,7 @@ all p (x:xs)    =  p x && all p xs
 -- 'False', the list must be finite; 'True', however, results from an element
 -- equal to @x@ found at a finite index of a finite or infinite list.
 elem                    :: (Eq a) => a -> [a] -> Bool
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 elem x                  =  any (== x)
 #else
 elem _ []       = False
@@ -808,7 +808,7 @@ elem x (y:ys)   = x==y || elem x ys
 
 -- | 'notElem' is the negation of 'elem'.
 notElem                 :: (Eq a) => a -> [a] -> Bool
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 notElem x               =  all (/= x)
 #else
 notElem _ []    =  True
@@ -855,7 +855,7 @@ concat = foldr (++) []
 -- It is an instance of the more general 'Data.List.genericIndex',
 -- which takes an index of any integral type.
 (!!)                    :: [a] -> Int -> a
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE)
 xs     !! n | n < 0 =  errorWithoutStackTrace "Prelude.!!: negative index"
 []     !! _         =  errorWithoutStackTrace "Prelude.!!: index too large"
 (x:_)  !! 0         =  x
diff --git a/libraries/base/GHC/Real.hs b/libraries/base/GHC/Real.hs
index 17d56c6d8a..1154091dd5 100644
--- a/libraries/base/GHC/Real.hs
+++ b/libraries/base/GHC/Real.hs
@@ -27,7 +27,7 @@ import GHC.Enum
 import GHC.Show
 import {-# SOURCE #-} GHC.Exception( divZeroException, overflowException, ratioZeroDenomException )
 
-#ifdef OPTIMISE_INTEGER_GCD_LCM
+#if defined(OPTIMISE_INTEGER_GCD_LCM)
 # if defined(MIN_VERSION_integer_gmp)
 import GHC.Integer.GMP.Internals
 # else
@@ -636,7 +636,7 @@ lcm _ 0         =  0
 lcm 0 _         =  0
 lcm x y         =  abs ((x `quot` (gcd x y)) * y)
 
-#ifdef OPTIMISE_INTEGER_GCD_LCM
+#if defined(OPTIMISE_INTEGER_GCD_LCM)
 {-# RULES
 "gcd/Int->Int->Int"             gcd = gcdInt'
 "gcd/Integer->Integer->Integer" gcd = gcdInteger
diff --git a/libraries/base/GHC/TopHandler.hs b/libraries/base/GHC/TopHandler.hs
index 58da871729..1b1e065831 100644
--- a/libraries/base/GHC/TopHandler.hs
+++ b/libraries/base/GHC/TopHandler.hs
@@ -94,7 +94,7 @@ runMainIO main =
       topHandler
 
 install_interrupt_handler :: IO () -> IO ()
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 install_interrupt_handler handler = do
   _ <- GHC.ConsoleHandler.installHandler $
      Catch $ \event ->
@@ -244,7 +244,7 @@ unreachable :: IO a
 unreachable = fail "If you can read this, shutdownHaskellAndExit did not exit."
 
 exitHelper :: CInt -> Int -> IO a
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 exitHelper exitKind r =
   shutdownHaskellAndExit (fromIntegral r) exitKind >> unreachable
 #else
@@ -266,7 +266,7 @@ foreign import ccall "shutdownHaskellAndSignal"
 
 exitInterrupted :: IO a
 exitInterrupted =
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   safeExit 252
 #else
   -- we must exit via the default action for SIGINT, so that the
diff --git a/libraries/base/System/Environment.hs b/libraries/base/System/Environment.hs
index 61b728cb9c..56e6961f8a 100644
--- a/libraries/base/System/Environment.hs
+++ b/libraries/base/System/Environment.hs
@@ -33,7 +33,7 @@ import Foreign
 import Foreign.C
 import System.IO.Error (mkIOError)
 import Control.Exception.Base (bracket_, throwIO)
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import Control.Exception.Base (bracket)
 #endif
 -- import GHC.IO
@@ -41,7 +41,7 @@ import GHC.IO.Exception
 import GHC.IO.Encoding (getFileSystemEncoding)
 import qualified GHC.Foreign as GHC
 import Control.Monad
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import GHC.Environment
 import GHC.Windows
 #else
@@ -50,7 +50,7 @@ import System.Posix.Internals (withFilePath)
 
 import System.Environment.ExecutablePath
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 # if defined(i386_HOST_ARCH)
 #  define WINDOWS_CCONV stdcall
 # elif defined(x86_64_HOST_ARCH)
@@ -65,7 +65,7 @@ import System.Environment.ExecutablePath
 -- ---------------------------------------------------------------------------
 -- getArgs, getProgName, getEnv
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 
 {-
 Note [Ignore hs_init argv]
@@ -133,7 +133,7 @@ dropRTSArgs (arg:rest)     = arg : dropRTSArgs rest
 -- line arguments (not including the program name).
 getArgs :: IO [String]
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 getArgs =  fmap tail getWin32ProgArgv_certainly
 #else
 getArgs =
@@ -160,7 +160,7 @@ between platforms: on Windows, for example, a program invoked as foo
 is probably really @FOO.EXE@, and that is what 'getProgName' will return.
 -}
 getProgName :: IO String
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 -- Ignore the arguments to hs_init on Windows for the sake of Unicode compat
 getProgName = fmap (basename . head) getWin32ProgArgv_certainly
 #else
@@ -188,7 +188,7 @@ basename f = go f f
 
   isPathSeparator :: Char -> Bool
   isPathSeparator '/'  = True
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
   isPathSeparator '\\' = True
 #endif
   isPathSeparator _    = False
@@ -206,7 +206,7 @@ basename f = go f f
 getEnv :: String -> IO String
 getEnv name = lookupEnv name >>= maybe handleError return
   where
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
     handleError = do
         err <- c_GetLastError
         if err == eRROR_ENVVAR_NOT_FOUND
@@ -230,7 +230,7 @@ foreign import WINDOWS_CCONV unsafe "windows.h GetLastError"
 --
 -- @since 4.6.0.0
 lookupEnv :: String -> IO (Maybe String)
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 lookupEnv name = withCWString name $ \s -> try_size s 256
   where
     try_size s size = allocaArray (fromIntegral size) $ \p_value -> do
@@ -295,7 +295,7 @@ setEnv key_ value_
     value = takeWhile (/= '\NUL') value_
 
 setEnv_ :: String -> String -> IO ()
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 setEnv_ key value = withCWString key $ \k -> withCWString value $ \v -> do
   success <- c_SetEnvironmentVariable k v
   unless success (throwGetLastError "setEnv")
@@ -329,7 +329,7 @@ foreign import ccall unsafe "putenv" c_putenv :: CString -> IO CInt
 --
 -- @since 4.7.0.0
 unsetEnv :: String -> IO ()
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 unsetEnv key = withCWString key $ \k -> do
   success <- c_SetEnvironmentVariable k nullPtr
   unless success $ do
@@ -340,7 +340,7 @@ unsetEnv key = withCWString key $ \k -> do
       throwGetLastError "unsetEnv"
 #else
 
-#ifdef HAVE_UNSETENV
+#if defined(HAVE_UNSETENV)
 unsetEnv key = withFilePath key (throwErrnoIf_ (/= 0) "unsetEnv" . c_unsetenv)
 foreign import ccall unsafe "__hsbase_unsetenv" c_unsetenv :: CString -> IO CInt
 #else
@@ -372,7 +372,7 @@ withProgName nm act = do
 
 withArgv :: [String] -> IO a -> IO a
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 -- We have to reflect the updated arguments in the RTS-side variables as
 -- well, because the RTS still consults them for error messages and the like.
 -- If we don't do this then ghc-e005 fails.
@@ -406,7 +406,7 @@ foreign import ccall unsafe "setProgArgv"
 -- the @key@ is the whole entry and the @value@ is the empty string.
 getEnvironment :: IO [(String, String)]
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 getEnvironment = bracket c_GetEnvironmentStrings c_FreeEnvironmentStrings $ \pBlock ->
     if pBlock == nullPtr then return []
      else go pBlock
diff --git a/libraries/base/System/IO.hs b/libraries/base/System/IO.hs
index 1796200bc4..735d41ba45 100644
--- a/libraries/base/System/IO.hs
+++ b/libraries/base/System/IO.hs
@@ -224,7 +224,7 @@ import Control.Exception.Base
 import Data.Bits
 import Data.Maybe
 import Foreign.C.Error
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 import Foreign.C.String
 #endif
 import Foreign.C.Types
@@ -546,7 +546,7 @@ openNewFile filepath binary mode = do
       errno <- getErrno
       case errno of
         _ | errno == eEXIST -> return FileExists
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
         -- If c_open throws EACCES on windows, it could mean that filepath is a
         -- directory. In this case, we want to return FileExists so that the
         -- enclosing openTempFile can try again instead of failing outright.
@@ -565,13 +565,13 @@ openNewFile filepath binary mode = do
         _ -> return (OpenNewError errno)
     else return (NewFileCreated fd)
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import ccall "file_exists" c_fileExists :: CString -> IO Bool
 #endif
 
 -- XXX Should use filepath library
 pathSeparator :: Char
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 pathSeparator = '\\'
 #else
 pathSeparator = '/'
diff --git a/libraries/base/System/Posix/Internals.hs b/libraries/base/System/Posix/Internals.hs
index 7bb26fa395..93ad4e8137 100644
--- a/libraries/base/System/Posix/Internals.hs
+++ b/libraries/base/System/Posix/Internals.hs
@@ -43,7 +43,7 @@ import GHC.IO
 import GHC.IO.IOMode
 import GHC.IO.Exception
 import GHC.IO.Device
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 import {-# SOURCE #-} GHC.IO.Encoding (getFileSystemEncoding)
 import qualified GHC.Foreign as GHC
 #endif
@@ -157,7 +157,7 @@ fdGetMode fd = do
 
     return mode
 
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 withFilePath :: FilePath -> (CWString -> IO a) -> IO a
 withFilePath = withCWString
 
@@ -545,7 +545,7 @@ s_isfifo cm = c_s_isfifo cm /= 0
 
 foreign import ccall unsafe "HsBase.h __hscore_sizeof_stat" sizeof_stat :: Int
 foreign import ccall unsafe "HsBase.h __hscore_st_mtime" st_mtime :: Ptr CStat -> IO CTime
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 foreign import ccall unsafe "HsBase.h __hscore_st_size" st_size :: Ptr CStat -> IO Int64
 #else
 foreign import ccall unsafe "HsBase.h __hscore_st_size" st_size :: Ptr CStat -> IO COff
diff --git a/libraries/base/System/Timeout.hs b/libraries/base/System/Timeout.hs
index d4ef0932b5..d34082e64f 100644
--- a/libraries/base/System/Timeout.hs
+++ b/libraries/base/System/Timeout.hs
@@ -18,7 +18,7 @@
 
 module System.Timeout ( timeout ) where
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 import Control.Monad
 import GHC.Event           (getSystemTimerManager,
                             registerTimeout, unregisterTimeout)
@@ -80,7 +80,7 @@ timeout :: Int -> IO a -> IO (Maybe a)
 timeout n f
     | n <  0    = fmap Just f
     | n == 0    = return Nothing
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
     | rtsSupportsBoundThreads = do
         -- In the threaded RTS, we use the Timer Manager to delay the
         -- (fairly expensive) 'forkIO' call until the timeout has expired.
diff --git a/libraries/base/cbits/SetEnv.c b/libraries/base/cbits/SetEnv.c
index 38f0ed52b8..7b6d2b584e 100644
--- a/libraries/base/cbits/SetEnv.c
+++ b/libraries/base/cbits/SetEnv.c
@@ -1,7 +1,7 @@
 #include "HsBase.h"
-#ifdef HAVE_UNSETENV
+#if defined(HAVE_UNSETENV)
 int __hsbase_unsetenv(const char *name) {
-#ifdef UNSETENV_RETURNS_VOID
+#if defined(UNSETENV_RETURNS_VOID)
     unsetenv(name);
     return 0;
 #else
diff --git a/libraries/base/cbits/iconv.c b/libraries/base/cbits/iconv.c
index 2246ca67db..e1123a43a1 100644
--- a/libraries/base/cbits/iconv.c
+++ b/libraries/base/cbits/iconv.c
@@ -1,4 +1,4 @@
-#ifndef _WIN32
+#if !defined(_WIN32)
 
 #include <stdlib.h>
 #include <iconv.h>
diff --git a/libraries/base/cbits/primFloat.c b/libraries/base/cbits/primFloat.c
index 4bee4d0ded..f0746775d3 100644
--- a/libraries/base/cbits/primFloat.c
+++ b/libraries/base/cbits/primFloat.c
@@ -109,7 +109,7 @@ union stg_ieee754_dbl
  */
 
 /* In case you don't support IEEE, you'll just get dummy defs.. */
-#ifdef IEEE_FLOATING_POINT
+#if defined(IEEE_FLOATING_POINT)
 
 HsInt
 isDoubleFinite(HsDouble d)
diff --git a/libraries/base/include/HsBase.h b/libraries/base/include/HsBase.h
index 8ee207431c..0fe5805a64 100644
--- a/libraries/base/include/HsBase.h
+++ b/libraries/base/include/HsBase.h
@@ -99,8 +99,8 @@
 #elif HAVE_STDINT_H
 # include <stdint.h>
 #endif
-#ifdef HAVE_CLOCK_GETTIME
-# ifdef _POSIX_MONOTONIC_CLOCK
+#if defined(HAVE_CLOCK_GETTIME)
+# if defined(_POSIX_MONOTONIC_CLOCK)
 #  define CLOCK_ID CLOCK_MONOTONIC
 # else
 #  define CLOCK_ID CLOCK_REALTIME
@@ -162,7 +162,7 @@ extern int fdReady(int fd, int write, int msecs, int isSock);
    when compiling to native code.
    -------------------------------------------------------------------------- */
 
-#ifndef INLINE
+#if !defined(INLINE)
 # if defined(_MSC_VER)
 #  define INLINE extern __inline
 # else
@@ -192,7 +192,7 @@ __hscore_o_binary(void)
 INLINE int
 __hscore_o_rdonly(void)
 {
-#ifdef O_RDONLY
+#if defined(O_RDONLY)
   return O_RDONLY;
 #else
   return 0;
@@ -202,7 +202,7 @@ __hscore_o_rdonly(void)
 INLINE int
 __hscore_o_wronly( void )
 {
-#ifdef O_WRONLY
+#if defined(O_WRONLY)
   return O_WRONLY;
 #else
   return 0;
@@ -212,7 +212,7 @@ __hscore_o_wronly( void )
 INLINE int
 __hscore_o_rdwr( void )
 {
-#ifdef O_RDWR
+#if defined(O_RDWR)
   return O_RDWR;
 #else
   return 0;
@@ -222,7 +222,7 @@ __hscore_o_rdwr( void )
 INLINE int
 __hscore_o_append( void )
 {
-#ifdef O_APPEND
+#if defined(O_APPEND)
   return O_APPEND;
 #else
   return 0;
@@ -232,7 +232,7 @@ __hscore_o_append( void )
 INLINE int
 __hscore_o_creat( void )
 {
-#ifdef O_CREAT
+#if defined(O_CREAT)
   return O_CREAT;
 #else
   return 0;
@@ -242,7 +242,7 @@ __hscore_o_creat( void )
 INLINE int
 __hscore_o_excl( void )
 {
-#ifdef O_EXCL
+#if defined(O_EXCL)
   return O_EXCL;
 #else
   return 0;
@@ -252,7 +252,7 @@ __hscore_o_excl( void )
 INLINE int
 __hscore_o_trunc( void )
 {
-#ifdef O_TRUNC
+#if defined(O_TRUNC)
   return O_TRUNC;
 #else
   return 0;
@@ -262,7 +262,7 @@ __hscore_o_trunc( void )
 INLINE int
 __hscore_o_noctty( void )
 {
-#ifdef O_NOCTTY
+#if defined(O_NOCTTY)
   return O_NOCTTY;
 #else
   return 0;
@@ -272,7 +272,7 @@ __hscore_o_noctty( void )
 INLINE int
 __hscore_o_nonblock( void )
 {
-#ifdef O_NONBLOCK
+#if defined(O_NONBLOCK)
   return O_NONBLOCK;
 #else
   return 0;
@@ -374,7 +374,7 @@ __hscore_ptr_c_cc( struct termios* ts )
 INLINE HsInt
 __hscore_sizeof_termios( void )
 {
-#ifndef _WIN32
+#if !defined(_WIN32)
   return sizeof(struct termios);
 #else
   return 0;
@@ -393,7 +393,7 @@ __hscore_sizeof_sigset_t( void )
 INLINE int
 __hscore_echo( void )
 {
-#ifdef ECHO
+#if defined(ECHO)
   return ECHO;
 #else
   return 0;
@@ -404,7 +404,7 @@ __hscore_echo( void )
 INLINE int
 __hscore_tcsanow( void )
 {
-#ifdef TCSANOW
+#if defined(TCSANOW)
   return TCSANOW;
 #else
   return 0;
@@ -415,7 +415,7 @@ __hscore_tcsanow( void )
 INLINE int
 __hscore_icanon( void )
 {
-#ifdef ICANON
+#if defined(ICANON)
   return ICANON;
 #else
   return 0;
@@ -424,7 +424,7 @@ __hscore_icanon( void )
 
 INLINE int __hscore_vmin( void )
 {
-#ifdef VMIN
+#if defined(VMIN)
   return VMIN;
 #else
   return 0;
@@ -433,7 +433,7 @@ INLINE int __hscore_vmin( void )
 
 INLINE int __hscore_vtime( void )
 {
-#ifdef VTIME
+#if defined(VTIME)
   return VTIME;
 #else
   return 0;
@@ -442,7 +442,7 @@ INLINE int __hscore_vtime( void )
 
 INLINE int __hscore_sigttou( void )
 {
-#ifdef SIGTTOU
+#if defined(SIGTTOU)
   return SIGTTOU;
 #else
   return 0;
@@ -451,7 +451,7 @@ INLINE int __hscore_sigttou( void )
 
 INLINE int __hscore_sig_block( void )
 {
-#ifdef SIG_BLOCK
+#if defined(SIG_BLOCK)
   return SIG_BLOCK;
 #else
   return 0;
@@ -460,14 +460,14 @@ INLINE int __hscore_sig_block( void )
 
 INLINE int __hscore_sig_setmask( void )
 {
-#ifdef SIG_SETMASK
+#if defined(SIG_SETMASK)
   return SIG_SETMASK;
 #else
   return 0;
 #endif
 }
 
-#ifndef _WIN32
+#if !defined(_WIN32)
 INLINE size_t __hscore_sizeof_siginfo_t (void)
 {
     return sizeof(siginfo_t);
@@ -477,7 +477,7 @@ INLINE size_t __hscore_sizeof_siginfo_t (void)
 INLINE int
 __hscore_f_getfl( void )
 {
-#ifdef F_GETFL
+#if defined(F_GETFL)
   return F_GETFL;
 #else
   return 0;
@@ -487,7 +487,7 @@ __hscore_f_getfl( void )
 INLINE int
 __hscore_f_setfl( void )
 {
-#ifdef F_SETFL
+#if defined(F_SETFL)
   return F_SETFL;
 #else
   return 0;
@@ -497,7 +497,7 @@ __hscore_f_setfl( void )
 INLINE int
 __hscore_f_setfd( void )
 {
-#ifdef F_SETFD
+#if defined(F_SETFD)
   return F_SETFD;
 #else
   return 0;
@@ -507,7 +507,7 @@ __hscore_f_setfd( void )
 INLINE long
 __hscore_fd_cloexec( void )
 {
-#ifdef FD_CLOEXEC
+#if defined(FD_CLOEXEC)
   return FD_CLOEXEC;
 #else
   return 0;
@@ -518,7 +518,7 @@ __hscore_fd_cloexec( void )
 extern void* __hscore_get_saved_termios(int fd);
 extern void __hscore_set_saved_termios(int fd, void* ts);
 
-#ifdef _WIN32
+#if defined(_WIN32)
 INLINE int __hscore_open(wchar_t *file, int how, mode_t mode) {
 	if ((how & O_WRONLY) || (how & O_RDWR) || (how & O_APPEND))
 	  return _wsopen(file,how | _O_NOINHERIT,_SH_DENYNO,mode);
diff --git a/libraries/base/include/ieee-flpt.h b/libraries/base/include/ieee-flpt.h
index a1fce3a8da..7bcfa1980e 100644
--- a/libraries/base/include/ieee-flpt.h
+++ b/libraries/base/include/ieee-flpt.h
@@ -4,32 +4,32 @@
 #define IEEE_FLOATING_POINT 1
 
    /* Radix of exponent representation */
-#ifndef FLT_RADIX
+#if !defined(FLT_RADIX)
 # define FLT_RADIX 2
 #endif
 
    /* Number of base-FLT_RADIX digits in the significand of a float */
-#ifndef FLT_MANT_DIG
+#if !defined(FLT_MANT_DIG)
 # define FLT_MANT_DIG 24
 #endif
    /* Minimum int x such that FLT_RADIX**(x-1) is a normalised float */
-#ifndef FLT_MIN_EXP
+#if !defined(FLT_MIN_EXP)
 #  define FLT_MIN_EXP (-125)
 #endif
    /* Maximum int x such that FLT_RADIX**(x-1) is a representable float */
-#ifndef FLT_MAX_EXP
+#if !defined(FLT_MAX_EXP)
 # define FLT_MAX_EXP 128
 #endif
 
    /* Number of base-FLT_RADIX digits in the significand of a double */
-#ifndef DBL_MANT_DIG
+#if !defined(DBL_MANT_DIG)
 # define DBL_MANT_DIG 53
 #endif
    /* Minimum int x such that FLT_RADIX**(x-1) is a normalised double */
-#ifndef DBL_MIN_EXP
+#if !defined(DBL_MIN_EXP)
 #  define DBL_MIN_EXP (-1021)
 #endif
    /* Maximum int x such that FLT_RADIX**(x-1) is a representable double */
-#ifndef DBL_MAX_EXP
+#if !defined(DBL_MAX_EXP)
 # define DBL_MAX_EXP 1024
 #endif
diff --git a/libraries/ghci/GHCi/ObjLink.hs b/libraries/ghci/GHCi/ObjLink.hs
index 3adb7ebaf9..0d7b2aeff8 100644
--- a/libraries/ghci/GHCi/ObjLink.hs
+++ b/libraries/ghci/GHCi/ObjLink.hs
@@ -180,14 +180,14 @@ foreign import ccall unsafe "removeLibrarySearchPath" c_removeLibrarySearchPath
 #include "ghcautoconf.h"
 
 cLeadingUnderscore :: Bool
-#ifdef LEADING_UNDERSCORE
+#if defined(LEADING_UNDERSCORE)
 cLeadingUnderscore = True
 #else
 cLeadingUnderscore = False
 #endif
 
 isWindowsHost :: Bool
-#ifdef mingw32_HOST_OS
+#if defined(mingw32_HOST_OS)
 isWindowsHost = True
 #else
 isWindowsHost = False
diff --git a/libraries/ghci/GHCi/Signals.hs b/libraries/ghci/GHCi/Signals.hs
index 9341b6ccab..629f116a0e 100644
--- a/libraries/ghci/GHCi/Signals.hs
+++ b/libraries/ghci/GHCi/Signals.hs
@@ -5,7 +5,7 @@ import Control.Concurrent
 import Control.Exception
 import System.Mem.Weak  ( deRefWeak )
 
-#ifndef mingw32_HOST_OS
+#if !defined(mingw32_HOST_OS)
 import System.Posix.Signals
 #endif