Remove redundant "do", "return" and language extensions from base

46 files changed, 191 insertions, 188 deletions

diff --git a/libraries/base/.hlint.yaml b/libraries/base/.hlint.yaml
index 6ebe02e94c..670eb5f6fb 100644
--- a/libraries/base/.hlint.yaml
+++ b/libraries/base/.hlint.yaml
@@ -5,3 +5,25 @@
 - ignore: {}
 - warn: {name: Unused LANGUAGE pragma}
 - warn: {name: Use fewer LANGUAGE pragmas}
+- warn: {name: Redundant return}
+- warn: {name: Redundant True guards}
+- warn: {name: Redundant do}
+- warn: {name: Redundant variable capture}
+- warn: {name: Redundant void}
+- warn: {name: Redundant as}
+- warn: {name: Use fewer imports}
+- warn: {name: Redundant as-pattern}
+- warn: {name: Redundant where}
+- warn: {name: Used otherwise as a pattern}
+
+
+## Exceptions
+# Sometimes, the hlint parser flags some functions and modules as incorrectly
+# using a language extension. Some other times, we need to make exceptions to
+# lints that we otherwise want applied elsewhere. Such exceptions are listed
+# below.
+
+- ignore: {name: Unused LANGUAGE pragma, within: [GHC.IO.Encoding.CodePage]}
+- ignore: {name: Redundant do, within: [GHC.IO.Handle.Text.commitBuffer]}
+- ignore: {name: Use fewer imports, within: [GHC.Windows]}
+- ignore: {name: Use fewer imports, within: [GHC.Event.Control]}
diff --git a/libraries/base/Control/Concurrent/Chan.hs b/libraries/base/Control/Concurrent/Chan.hs
index 874e48a1a1..1599ae3048 100644
--- a/libraries/base/Control/Concurrent/Chan.hs
+++ b/libraries/base/Control/Concurrent/Chan.hs
@@ -105,7 +105,7 @@ writeChan (Chan _ writeVar) val = do
 -- Throws 'Control.Exception.BlockedIndefinitelyOnMVar' when the channel is
 -- empty and no other thread holds a reference to the channel.
 readChan :: Chan a -> IO a
-readChan (Chan readVar _) = do
+readChan (Chan readVar _) =
   modifyMVar readVar $ \read_end -> do
     (ChItem val new_read_end) <- readMVar read_end
         -- Use readMVar here, not takeMVar,
diff --git a/libraries/base/Control/Concurrent/QSem.hs b/libraries/base/Control/Concurrent/QSem.hs
index 133d6e2ab8..9f53eef826 100644
--- a/libraries/base/Control/Concurrent/QSem.hs
+++ b/libraries/base/Control/Concurrent/QSem.hs
@@ -82,7 +82,7 @@ waitQSem (QSem m) =
          putMVar m (z, b1, b2)
          return ()
   where
-    wait b = takeMVar b `onException` do
+    wait b = takeMVar b `onException`
                 (uninterruptibleMask_ $ do -- Note [signal uninterruptible]
                    (i,b1,b2) <- takeMVar m
                    r <- tryTakeMVar b
diff --git a/libraries/base/Control/Concurrent/QSemN.hs b/libraries/base/Control/Concurrent/QSemN.hs
index ea3236b0a4..1262198796 100644
--- a/libraries/base/Control/Concurrent/QSemN.hs
+++ b/libraries/base/Control/Concurrent/QSemN.hs
@@ -93,7 +93,7 @@ waitQSemN qs@(QSemN m) sz = mask_ $ do
     JustMV b -> wait b
   where
     wait :: MVar () -> IO ()
-    wait b = do
+    wait b =
       takeMVar b `onException` do
         already_filled <- not <$> tryPutMVar b ()
         when already_filled $ signalQSemN qs sz
diff --git a/libraries/base/Control/Monad/ST/Lazy/Imp.hs b/libraries/base/Control/Monad/ST/Lazy/Imp.hs
index db900d9579..de8310c76d 100644
--- a/libraries/base/Control/Monad/ST/Lazy/Imp.hs
+++ b/libraries/base/Control/Monad/ST/Lazy/Imp.hs
@@ -42,7 +42,7 @@ import Control.Monad.Fix
 import qualified Control.Monad.ST as ST
 import qualified Control.Monad.ST.Unsafe as ST
 
-import qualified GHC.ST as GHC.ST
+import qualified GHC.ST
 import GHC.Base
 
 -- | The lazy @'ST'@ monad.
diff --git a/libraries/base/Data/String.hs b/libraries/base/Data/String.hs
index e091dab86f..79a32ce322 100644
--- a/libraries/base/Data/String.hs
+++ b/libraries/base/Data/String.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE StandaloneDeriving #-}
diff --git a/libraries/base/Debug/Trace.hs b/libraries/base/Debug/Trace.hs
index 1b977bae6e..453b5141b4 100644
--- a/libraries/base/Debug/Trace.hs
+++ b/libraries/base/Debug/Trace.hs
@@ -78,7 +78,7 @@ import Data.List (null, partition)
 --
 -- @since 4.5.0.0
 traceIO :: String -> IO ()
-traceIO msg = do
+traceIO msg =
     withCString "%s\n" $ \cfmt -> do
      -- NB: debugBelch can't deal with null bytes, so filter them
      -- out so we don't accidentally truncate the message.  See #9395
diff --git a/libraries/base/Foreign/Marshal/Array.hs b/libraries/base/Foreign/Marshal/Array.hs
index c0a9164b51..e494cdaca6 100644
--- a/libraries/base/Foreign/Marshal/Array.hs
+++ b/libraries/base/Foreign/Marshal/Array.hs
@@ -214,12 +214,10 @@ withArrayLen0 :: Storable a => a -> [a] -> (Int -> Ptr a -> IO b) -> IO b
 withArrayLen0 marker vals f  =
   allocaArray0 len $ \ptr -> do
       pokeArray0 marker ptr vals
-      res <- f len ptr
-      return res
+      f len ptr
   where
     len = length vals
 
-
 -- copying (argument order: destination, source)
 -- -------
 
diff --git a/libraries/base/Foreign/Marshal/Utils.hs b/libraries/base/Foreign/Marshal/Utils.hs
index f6bec7aacb..d134788e62 100644
--- a/libraries/base/Foreign/Marshal/Utils.hs
+++ b/libraries/base/Foreign/Marshal/Utils.hs
@@ -89,9 +89,7 @@ with       :: Storable a => a -> (Ptr a -> IO b) -> IO b
 with val f  =
   alloca $ \ptr -> do
     poke ptr val
-    res <- f ptr
-    return res
-
+    f ptr
 
 -- marshalling of Boolean values (non-zero corresponds to 'True')
 -- -----------------------------
diff --git a/libraries/base/GHC/Conc/POSIX.hs b/libraries/base/GHC/Conc/POSIX.hs
index 84dc68fc30..3a6ddf2287 100644
--- a/libraries/base/GHC/Conc/POSIX.hs
+++ b/libraries/base/GHC/Conc/POSIX.hs
@@ -179,7 +179,7 @@ interruptIOManager :: IO ()
 interruptIOManager = return ()
 
 startIOManagerThread :: IO ()
-startIOManagerThread = do
+startIOManagerThread =
   modifyMVar_ ioManagerThread $ \old -> do
     let create = do t <- forkIO ioManager;
                     labelThread t "IOManagerThread";
@@ -251,7 +251,7 @@ service_loop wakeup old_delays = do
 
   r <- c_WaitForSingleObject wakeup timeout
   case r of
-    0xffffffff -> do throwGetLastError "service_loop"
+    0xffffffff -> throwGetLastError "service_loop"
     0 -> do
         r2 <- c_readIOManagerEvent
         exit <-
diff --git a/libraries/base/GHC/Environment.hs b/libraries/base/GHC/Environment.hs
index 4db0837664..eb30434f40 100644
--- a/libraries/base/GHC/Environment.hs
+++ b/libraries/base/GHC/Environment.hs
@@ -26,8 +26,8 @@ import qualified GHC.Foreign as GHC
 -- returns a list of the program's command line arguments, starting with the
 -- program name, and including those normally eaten by the RTS (+RTS ... -RTS).
 getFullArgs :: IO [String]
-getFullArgs = do
-  alloca $ \ p_argc -> do
+getFullArgs =
+  alloca $ \ p_argc ->
     alloca $ \ p_argv -> do
         getFullProgArgv p_argc p_argv
         p    <- fromIntegral `liftM` peek p_argc
diff --git a/libraries/base/GHC/Event/Array.hs b/libraries/base/GHC/Event/Array.hs
index 9558ece576..a24f5f34c1 100644
--- a/libraries/base/GHC/Event/Array.hs
+++ b/libraries/base/GHC/Event/Array.hs
@@ -128,7 +128,7 @@ unsafeWrite (Array ref) ix a = do
     unsafeWrite' ac ix a
 
 unsafeWrite' :: Storable a => AC a -> Int -> a -> IO ()
-unsafeWrite' (AC es _ cap) ix a = do
+unsafeWrite' (AC es _ cap) ix a =
     CHECK_BOUNDS("unsafeWrite'",cap,ix)
       withForeignPtr es $ \p ->
         pokeElemOff p ix a
@@ -158,7 +158,7 @@ ensureCapacity (Array ref) c = do
       writeIORef ref ac'
 
 ensureCapacity' :: Storable a => AC a -> Int -> IO (AC a)
-ensureCapacity' ac@(AC es len cap) c = do
+ensureCapacity' ac@(AC es len cap) c =
     if c > cap
       then do
         es' <- reallocArray es cap' cap
@@ -182,7 +182,7 @@ snoc (Array ref) e = do
     writeIORef ref (AC es len' cap)
 
 clear :: Array a -> IO ()
-clear (Array ref) = do
+clear (Array ref) =
   atomicModifyIORef' ref $ \(AC es _ cap) ->
         (AC es 0 cap, ())
 
diff --git a/libraries/base/GHC/Event/Control.hs b/libraries/base/GHC/Event/Control.hs
index 779d60d5d7..a9f23e07d2 100644
--- a/libraries/base/GHC/Event/Control.hs
+++ b/libraries/base/GHC/Event/Control.hs
@@ -28,7 +28,6 @@ module GHC.Event.Control
 
 #include "EventConfig.h"
 
-import Foreign.ForeignPtr (ForeignPtr)
 import GHC.Base
 import GHC.IORef
 import GHC.Conc.Signal (Signal)
@@ -37,7 +36,7 @@ import GHC.Show (Show)
 import GHC.Word (Word8)
 import Foreign.C.Error (throwErrnoIfMinus1_, throwErrno, getErrno)
 import Foreign.C.Types (CInt(..), CSize(..))
-import Foreign.ForeignPtr (mallocForeignPtrBytes, withForeignPtr)
+import Foreign.ForeignPtr (ForeignPtr, mallocForeignPtrBytes, withForeignPtr)
 import Foreign.Marshal (alloca, allocaBytes)
 import Foreign.Marshal.Array (allocaArray)
 import Foreign.Ptr (castPtr)
diff --git a/libraries/base/GHC/Event/Manager.hs b/libraries/base/GHC/Event/Manager.hs
index b680a54e77..dd133798d7 100644
--- a/libraries/base/GHC/Event/Manager.hs
+++ b/libraries/base/GHC/Event/Manager.hs
@@ -492,8 +492,8 @@ onFdEvent mgr fd evs
                 -- if there are no saved events and we registered with one-shot
                 -- semantics then there is no need to re-arm
                 unless (OneShot == I.elLifetime allEls
-                        && mempty == I.elEvent savedEls) $ do
-                  void $ I.modifyFdOnce (emBackend mgr) fd (I.elEvent savedEls)
+                  && mempty == I.elEvent savedEls) $
+                    void $ I.modifyFdOnce (emBackend mgr) fd (I.elEvent savedEls)
               _ ->
                 -- we need to re-arm with multi-shot semantics
                 void $ I.modifyFd (emBackend mgr) fd
diff --git a/libraries/base/GHC/Event/Thread.hs b/libraries/base/GHC/Event/Thread.hs
index fb40cde4d0..367791354f 100644
--- a/libraries/base/GHC/Event/Thread.hs
+++ b/libraries/base/GHC/Event/Thread.hs
@@ -197,8 +197,7 @@ eventManager = unsafePerformIO $ do
 {-# NOINLINE eventManager #-}
 
 numEnabledEventManagers :: IORef Int
-numEnabledEventManagers = unsafePerformIO $ do
-  newIORef 0
+numEnabledEventManagers = unsafePerformIO $ newIORef 0
 {-# NOINLINE numEnabledEventManagers #-}
 
 foreign import ccall unsafe "getOrSetSystemEventThreadIOManagerThreadStore"
@@ -213,10 +212,10 @@ ioManagerLock = unsafePerformIO $ do
    sharedCAF m getOrSetSystemEventThreadIOManagerThreadStore
 
 getSystemTimerManager :: IO TM.TimerManager
-getSystemTimerManager = do
+getSystemTimerManager =
   fromMaybe err `fmap` readIORef timerManager
-  where
-    err = error "GHC.Event.Thread.getSystemTimerManager: the TimerManager requires linking against the threaded runtime"
+    where
+      err = error "GHC.Event.Thread.getSystemTimerManager: the TimerManager requires linking against the threaded runtime"
 
 foreign import ccall unsafe "getOrSetSystemTimerThreadEventManagerStore"
     getOrSetSystemTimerThreadEventManagerStore :: Ptr a -> IO (Ptr a)
@@ -325,7 +324,7 @@ startTimerManagerThread = modifyMVar_ timerManagerThreadVar $ \old -> do
 foreign import ccall unsafe "rtsSupportsBoundThreads" threaded :: Bool
 
 ioManagerCapabilitiesChanged :: IO ()
-ioManagerCapabilitiesChanged = do
+ioManagerCapabilitiesChanged =
   withMVar ioManagerLock $ \_ -> do
     new_n_caps <- getNumCapabilities
     numEnabled <- readIORef numEnabledEventManagers
diff --git a/libraries/base/GHC/Event/TimerManager.hs b/libraries/base/GHC/Event/TimerManager.hs
index 4cac18d9a0..533558a8cc 100644
--- a/libraries/base/GHC/Event/TimerManager.hs
+++ b/libraries/base/GHC/Event/TimerManager.hs
@@ -226,7 +226,7 @@ registerTimeout mgr us cb = do
 
 -- | Unregister an active timeout.
 unregisterTimeout :: TimerManager -> TimeoutKey -> IO ()
-unregisterTimeout mgr (TK key) = do
+unregisterTimeout mgr (TK key) =
   editTimeouts mgr (Q.delete key)
 
 -- | Update an active timeout to fire in the given number of
diff --git a/libraries/base/GHC/Fingerprint.hs b/libraries/base/GHC/Fingerprint.hs
index 18bf0f9b36..06c4e856e0 100644
--- a/libraries/base/GHC/Fingerprint.hs
+++ b/libraries/base/GHC/Fingerprint.hs
@@ -42,11 +42,11 @@ fingerprint0 = Fingerprint 0 0
 
 fingerprintFingerprints :: [Fingerprint] -> Fingerprint
 fingerprintFingerprints fs = unsafeDupablePerformIO $
-  withArrayLen fs $ \len p -> do
+  withArrayLen fs $ \len p ->
     fingerprintData (castPtr p) (len * sizeOf (head fs))
 
 fingerprintData :: Ptr Word8 -> Int -> IO Fingerprint
-fingerprintData buf len = do
+fingerprintData buf len =
   allocaBytes SIZEOF_STRUCT_MD5CONTEXT $ \pctxt -> do
     c_MD5Init pctxt
     c_MD5Update pctxt buf (fromIntegral len)
@@ -71,7 +71,7 @@ fingerprintString str = unsafeDupablePerformIO $
 --
 -- @since 4.7.0.0
 getFileHash :: FilePath -> IO Fingerprint
-getFileHash path = withBinaryFile path ReadMode $ \h -> do
+getFileHash path = withBinaryFile path ReadMode $ \h ->
   allocaBytes SIZEOF_STRUCT_MD5CONTEXT $ \pctxt -> do
     c_MD5Init pctxt
 
diff --git a/libraries/base/GHC/IO/Buffer.hs b/libraries/base/GHC/IO/Buffer.hs
index 167bc2a346..e062cbfc0b 100644
--- a/libraries/base/GHC/IO/Buffer.hs
+++ b/libraries/base/GHC/IO/Buffer.hs
@@ -319,7 +319,7 @@ summaryBuffer !buf  -- Strict => slightly better code
 --     operation, a read buffer always has at least one character of space.
 
 checkBuffer :: Buffer a -> IO ()
-checkBuffer buf@Buffer{ bufState = state, bufL=r, bufR=w, bufSize=size } = do
+checkBuffer buf@Buffer{ bufState = state, bufL=r, bufR=w, bufSize=size } =
      check buf (
         size > 0
         && r <= w
diff --git a/libraries/base/GHC/IO/Encoding/Failure.hs b/libraries/base/GHC/IO/Encoding/Failure.hs
index c8d29f4d50..271d66b35f 100644
--- a/libraries/base/GHC/IO/Encoding/Failure.hs
+++ b/libraries/base/GHC/IO/Encoding/Failure.hs
@@ -146,7 +146,7 @@ unescapeRoundtripCharacterSurrogate c
 recoverDecode :: CodingFailureMode -> Buffer Word8 -> Buffer Char
               -> IO (Buffer Word8, Buffer Char)
 recoverDecode cfm input@Buffer{  bufRaw=iraw, bufL=ir, bufR=_  }
-                  output@Buffer{ bufRaw=oraw, bufL=_,  bufR=ow } = do
+                  output@Buffer{ bufRaw=oraw, bufL=_,  bufR=ow } =
  --puts $ "recoverDecode " ++ show ir
  case cfm of
   ErrorOnCodingFailure       -> ioe_decodingError
diff --git a/libraries/base/GHC/IO/Encoding/Iconv.hs b/libraries/base/GHC/IO/Encoding/Iconv.hs
index d1db6cd718..6c120cae58 100644
--- a/libraries/base/GHC/IO/Encoding/Iconv.hs
+++ b/libraries/base/GHC/IO/Encoding/Iconv.hs
@@ -177,7 +177,7 @@ iconvRecode iconv_t
       iconv_trace ("iconvRecode after,  input=" ++ show (summaryBuffer new_input))
       iconv_trace ("iconvRecode after,  output=" ++ show (summaryBuffer new_output))
       if (res /= -1)
-        then do -- all input translated
+        then -- all input translated
            return (InputUnderflow, new_input, new_output)
         else do
       errno <- getErrno
diff --git a/libraries/base/GHC/IO/FD.hs b/libraries/base/GHC/IO/FD.hs
index 4245bf0b26..277a7b41c2 100644
--- a/libraries/base/GHC/IO/FD.hs
+++ b/libraries/base/GHC/IO/FD.hs
@@ -379,8 +379,8 @@ getSize :: FD -> IO Integer
 getSize fd = fdFileSize (fdFD fd)
 
 setSize :: FD -> Integer -> IO ()
-setSize fd size = do
-  throwErrnoIf_ (/=0) "GHC.IO.FD.setSize"  $
+setSize fd size =
+  throwErrnoIf_ (/=0) "GHC.IO.FD.setSize" $
      c_ftruncate (fdFD fd) (fromIntegral size)
 
 devType :: FD -> IO IODeviceType
@@ -689,7 +689,7 @@ throwErrnoIfMinus1RetryOnBlock loc f on_block  =
         if err == eINTR
           then throwErrnoIfMinus1RetryOnBlock loc f on_block
           else if err == eWOULDBLOCK || err == eAGAIN
-                 then do on_block
+                 then on_block
                  else throwErrno loc
       else return res
 #endif
diff --git a/libraries/base/GHC/IO/Handle.hs b/libraries/base/GHC/IO/Handle.hs
index f62acc1510..2ad608b0df 100644
--- a/libraries/base/GHC/IO/Handle.hs
+++ b/libraries/base/GHC/IO/Handle.hs
@@ -266,7 +266,7 @@ hSetBuffering handle mode =
 -- the encoding.
 --
 hSetEncoding :: Handle -> TextEncoding -> IO ()
-hSetEncoding hdl encoding = do
+hSetEncoding hdl encoding =
   withAllHandles__ "hSetEncoding" hdl $ \h_@Handle__{..} -> do
     flushCharBuffer h_
     closeTextCodecs h_
@@ -579,7 +579,7 @@ hGetEcho handle = do
 -- | Is the handle connected to a terminal?
 
 hIsTerminalDevice :: Handle -> IO Bool
-hIsTerminalDevice handle = do
+hIsTerminalDevice handle =
     withHandle_ "hIsTerminalDevice" handle $ \ Handle__{..} -> do
      case haType of
        ClosedHandle -> ioe_closedHandle
@@ -641,7 +641,7 @@ hSetNewlineMode handle NewlineMode{ inputNL=i, outputNL=o } =
 -- before the handle is duplicated.
 
 hDuplicate :: Handle -> IO Handle
-hDuplicate h@(FileHandle path m) = do
+hDuplicate h@(FileHandle path m) =
   withHandle_' "hDuplicate" h m $ \h_ ->
       dupHandle path h Nothing h_ (Just handleFinalizer)
 hDuplicate h@(DuplexHandle path r w) = do
@@ -667,7 +667,7 @@ dupHandle filepath h other_side h_@Handle__{..} mb_finalizer = do
        new_dev <- IODevice.dup haDevice
        dupHandle_ new_dev filepath other_side h_ mb_finalizer
     Just r  ->
-       withHandle_' "dupHandle" h r $ \Handle__{haDevice=dev} -> do
+       withHandle_' "dupHandle" h r $ \Handle__{haDevice=dev} ->
          dupHandle_ dev filepath other_side h_ mb_finalizer
 
 dupHandle_ :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => dev
@@ -697,19 +697,19 @@ This can be used to retarget the standard Handles, for example:
 -}
 
 hDuplicateTo :: Handle -> Handle -> IO ()
-hDuplicateTo h1@(FileHandle path m1) h2@(FileHandle _ m2)  = do
+hDuplicateTo h1@(FileHandle path m1) h2@(FileHandle _ m2) =
  withHandle__' "hDuplicateTo" h2 m2 $ \h2_ -> do
    try $ flushWriteBuffer h2_
-   withHandle_' "hDuplicateTo" h1 m1 $ \h1_ -> do
+   withHandle_' "hDuplicateTo" h1 m1 $ \h1_ ->
      dupHandleTo path h1 Nothing h2_ h1_ (Just handleFinalizer)
 hDuplicateTo h1@(DuplexHandle path r1 w1) h2@(DuplexHandle _ r2 w2)  = do
  withHandle__' "hDuplicateTo" h2 w2  $ \w2_ -> do
    try $ flushWriteBuffer w2_
-   withHandle_' "hDuplicateTo" h1 w1 $ \w1_ -> do
+   withHandle_' "hDuplicateTo" h1 w1 $ \w1_ ->
      dupHandleTo path h1 Nothing w2_ w1_ (Just handleFinalizer)
  withHandle__' "hDuplicateTo" h2 r2  $ \r2_ -> do
    try $ flushWriteBuffer r2_
-   withHandle_' "hDuplicateTo" h1 r1 $ \r1_ -> do
+   withHandle_' "hDuplicateTo" h1 r1 $ \r1_ ->
      dupHandleTo path h1 (Just w1) r2_ r1_ Nothing
 hDuplicateTo h1 _ =
   ioe_dupHandlesNotCompatible h1
diff --git a/libraries/base/GHC/IO/Handle/Internals.hs b/libraries/base/GHC/IO/Handle/Internals.hs
index 120ae0ea66..d5f53b7dd5 100644
--- a/libraries/base/GHC/IO/Handle/Internals.hs
+++ b/libraries/base/GHC/IO/Handle/Internals.hs
@@ -477,10 +477,10 @@ flushBuffer :: Handle__ -> IO ()
 flushBuffer h_@Handle__{..} = do
   buf <- readIORef haCharBuffer
   case bufState buf of
-    ReadBuffer  -> do
+    ReadBuffer -> do
         flushCharReadBuffer h_
         flushByteReadBuffer h_
-    WriteBuffer -> do
+    WriteBuffer ->
         flushByteWriteBuffer h_
 
 -- | flushes the Char buffer only.  Works on all Handles.
@@ -488,7 +488,7 @@ flushCharBuffer :: Handle__ -> IO ()
 flushCharBuffer h_@Handle__{..} = do
   cbuf <- readIORef haCharBuffer
   case bufState cbuf of
-    ReadBuffer  -> do
+    ReadBuffer ->
         flushCharReadBuffer h_
     WriteBuffer ->
         -- Nothing to do here. Char buffer on a write Handle is always empty
@@ -581,7 +581,7 @@ flushCharReadBuffer Handle__{..} = do
      else do
 
   case haDecoder of
-    Nothing -> do
+    Nothing ->
       writeIORef haByteBuffer bbuf0 { bufL = bufL bbuf0 + bufL cbuf0 }
       -- no decoder: the number of bytes to decode is the same as the
       -- number of chars we have used up.
@@ -713,7 +713,7 @@ mkFileHandle :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev)
              -> NewlineMode
                     -- Translate newlines?
              -> IO Handle
-mkFileHandle dev filepath iomode mb_codec tr_newlines = do
+mkFileHandle dev filepath iomode mb_codec tr_newlines =
    mkHandle dev filepath (ioModeToHandleType iomode) True{-buffered-} mb_codec
             tr_newlines
             (Just handleFinalizer) Nothing{-other_side-}
diff --git a/libraries/base/GHC/IO/Handle/Text.hs b/libraries/base/GHC/IO/Handle/Text.hs
index 6d63bb0d54..fa5428cb35 100644
--- a/libraries/base/GHC/IO/Handle/Text.hs
+++ b/libraries/base/GHC/IO/Handle/Text.hs
@@ -87,7 +87,7 @@ import GHC.List
 --
 
 hWaitForInput :: Handle -> Int -> IO Bool
-hWaitForInput h msecs = do
+hWaitForInput h msecs =
   wantReadableHandle_ "hWaitForInput" h $ \ handle_@Handle__{..} -> do
   cbuf <- readIORef haCharBuffer
 
@@ -185,8 +185,8 @@ hGetChar handle =
 
 hGetLine :: Handle -> IO String
 hGetLine h =
-  wantReadableHandle_ "hGetLine" h $ \ handle_ -> do
-     hGetLineBuffered handle_
+  wantReadableHandle_ "hGetLine" h $ \ handle_ ->
+    hGetLineBuffered handle_
 
 hGetLineBuffered :: Handle__ -> IO String
 hGetLineBuffered handle_@Handle__{..} = do
@@ -299,12 +299,12 @@ unpack_nl !buf !r !w acc0
               c <- peekElemOff pbuf i
               if (c == '\n' && i > r)
                  then do
-                         c1 <- peekElemOff pbuf (i-1)
-                         if (c1 == '\r')
-                            then unpackRB ('\n':acc) (i-2)
-                            else unpackRB ('\n':acc) (i-1)
-                 else do
-                         unpackRB (c : acc) (i-1)
+                   c1 <- peekElemOff pbuf (i-1)
+                   if (c1 == '\r')
+                      then unpackRB ('\n':acc) (i-2)
+                      else unpackRB ('\n':acc) (i-1)
+                 else
+                   unpackRB (c : acc) (i-1)
      in do
      c <- peekElemOff pbuf (w-1)
      if (c == '\r')
@@ -437,15 +437,16 @@ getSomeCharacters handle_@Handle__{..} buf@Buffer{..} =
     1 | haInputNL == CRLF -> do
       (c,_) <- readCharBuf bufRaw bufL
       if c == '\r'
-         then do -- shuffle the '\r' to the beginning.  This is only safe
-                 -- if we're about to call readTextDevice, otherwise it
-                 -- would mess up flushCharBuffer.
-                 -- See [note Buffer Flushing], GHC.IO.Handle.Types
-                 _ <- writeCharBuf bufRaw 0 '\r'
-                 let buf' = buf{ bufL=0, bufR=1 }
-                 readTextDevice handle_ buf'
-         else do
-                 return buf
+      then do
+        -- shuffle the '\r' to the beginning.  This is only safe
+        -- if we're about to call readTextDevice, otherwise it
+        -- would mess up flushCharBuffer.
+        -- See [note Buffer Flushing], GHC.IO.Handle.Types
+        _ <- writeCharBuf bufRaw 0 '\r'
+        let buf' = buf{ bufL=0, bufR=1 }
+        readTextDevice handle_ buf'
+      else
+        return buf
 
     -- buffer has some chars in it already: just return it
     _otherwise ->
@@ -551,27 +552,27 @@ lazyBuffersToString CRLF = loop '\0' where
 hPutChar :: Handle -> Char -> IO ()
 hPutChar handle c = do
     c `seq` return ()
-    wantWritableHandle "hPutChar" handle $ \ handle_  -> do
-     hPutcBuffered handle_ c
+    wantWritableHandle "hPutChar" handle $ \ handle_  ->
+      hPutcBuffered handle_ c
 
 hPutcBuffered :: Handle__ -> Char -> IO ()
 hPutcBuffered handle_@Handle__{..} c = do
   buf <- readIORef haCharBuffer
   if c == '\n'
      then do buf1 <- if haOutputNL == CRLF
-                        then do
-                          buf1 <- putc buf '\r'
-                          putc buf1 '\n'
-                        else do
-                          putc buf '\n'
+                     then do
+                       buf1 <- putc buf '\r'
+                       putc buf1 '\n'
+                     else
+                       putc buf '\n'
              writeCharBuffer handle_ buf1
-             when is_line $ flushByteWriteBuffer handle_
+             when isLine $ flushByteWriteBuffer handle_
       else do
           buf1 <- putc buf c
           writeCharBuffer handle_ buf1
           return ()
   where
-    is_line = case haBufferMode of
+    isLine = case haBufferMode of
                 LineBuffering -> True
                 _             -> False
 
@@ -632,9 +633,9 @@ hPutStr' handle str add_nl =
        (NoBuffering, _) -> do
             hPutChars handle str        -- v. slow, but we don't care
             when add_nl $ hPutChar handle '\n'
-       (LineBuffering, buf) -> do
+       (LineBuffering, buf) ->
             writeBlocks handle True  add_nl nl buf str
-       (BlockBuffering _, buf) -> do
+       (BlockBuffering _, buf) ->
             writeBlocks handle False add_nl nl buf str
 
 hPutChars :: Handle -> [Char] -> IO ()
@@ -643,10 +644,7 @@ hPutChars handle (c:cs) = hPutChar handle c >> hPutChars handle cs
 
 -- Buffer offset is always zero.
 getSpareBuffer :: Handle__ -> IO (BufferMode, CharBuffer)
-getSpareBuffer Handle__{haCharBuffer=ref,
-                        haBuffers=spare_ref,
-                        haBufferMode=mode}
- = do
+getSpareBuffer Handle__{haCharBuffer=ref, haBuffers=spare_ref, haBufferMode=mode} =
    case mode of
      NoBuffering -> return (mode, errorWithoutStackTrace "no buffer!")
      _ -> do
@@ -667,9 +665,9 @@ writeBlocks hdl line_buffered add_nl nl
             buf@Buffer{ bufRaw=raw, bufSize=len } s =
   let
    shoveString :: Int -> [Char] -> [Char] -> IO ()
-   shoveString !n [] [] = do
+   shoveString !n [] [] =
         commitBuffer hdl raw len n False{-no flush-} True{-release-}
-   shoveString !n [] rest = do
+   shoveString !n [] rest =
         shoveString n rest []
    shoveString !n (c:cs) rest
      -- n+1 so we have enough room to write '\r\n' if necessary
@@ -678,18 +676,18 @@ writeBlocks hdl line_buffered add_nl nl
         shoveString 0 (c:cs) rest
      | c == '\n'  =  do
         n' <- if nl == CRLF
-                 then do
-                    n1 <- writeCharBuf raw n  '\r'
-                    writeCharBuf raw n1 '\n'
-                 else do
-                    writeCharBuf raw n c
+              then do
+                n1 <- writeCharBuf raw n  '\r'
+                writeCharBuf raw n1 '\n'
+              else
+                writeCharBuf raw n c
         if line_buffered
-           then do
-                -- end of line, so write and flush
-               commitBuffer hdl raw len n' True{-flush-} False
-               shoveString 0 cs rest
-           else do
-               shoveString n' cs rest
+        then do
+          -- end of line, so write and flush
+          commitBuffer hdl raw len n' True{-flush-} False
+          shoveString 0 cs rest
+        else
+          shoveString n' cs rest
      | otherwise = do
         n' <- writeCharBuf raw n c
         shoveString n' cs rest
@@ -701,36 +699,31 @@ writeBlocks hdl line_buffered add_nl nl
 --
 -- Write the contents of the buffer 'buf' ('sz' bytes long, containing
 -- 'count' bytes of data) to handle (handle must be block or line buffered).
-commitBuffer
-        :: Handle                       -- handle to commit to
-        -> RawCharBuffer -> Int         -- address and size (in bytes) of buffer
-        -> Int                          -- number of bytes of data in buffer
-        -> Bool                         -- True <=> flush the handle afterward
-        -> Bool                         -- release the buffer?
-        -> IO ()
-
+commitBuffer :: Handle                       -- handle to commit to
+             -> RawCharBuffer -> Int         -- address and size (in bytes) of buffer
+             -> Int                          -- number of bytes of data in buffer
+             -> Bool                         -- True <=> flush the handle afterward
+             -> Bool                         -- release the buffer?
+             -> IO ()
 commitBuffer hdl !raw !sz !count flush release =
   wantWritableHandle "commitBuffer" hdl $ \h_@Handle__{..} -> do
-      debugIO ("commitBuffer: sz=" ++ show sz ++ ", count=" ++ show count
-            ++ ", flush=" ++ show flush ++ ", release=" ++ show release ++ ", handle=" ++ show hdl)
-
+    let debugMsg = ("commitBuffer: sz=" ++ show sz ++ ", count=" ++ show count
+                    ++ ", flush=" ++ show flush ++ ", release=" ++ show release
+                    ++ ", handle=" ++ show hdl)
+    debugIO debugMsg
       -- Offset taken from handle
-      writeCharBuffer h_ Buffer{ bufRaw=raw, bufState=WriteBuffer, bufOffset=0,
-                                 bufL=0, bufR=count, bufSize=sz }
-
-      when flush $ flushByteWriteBuffer h_
-
-      -- release the buffer if necessary
-      when release $ do
-          -- find size of current buffer
-          old_buf@Buffer{ bufSize=size } <- readIORef haCharBuffer
-          when (sz == size) $ do
-               spare_bufs <- readIORef haBuffers
-               writeIORef haBuffers (BufferListCons raw spare_bufs)
-
-      -- bb <- readIORef haByteBuffer
-      -- debugIO ("commitBuffer: buffer=" ++ summaryBuffer bb ++ ", handle=" ++ show hdl)
-      return ()
+    writeCharBuffer h_ Buffer{ bufRaw=raw, bufState=WriteBuffer, bufOffset=0,
+                               bufL=0, bufR=count, bufSize=sz }
+    when flush $ flushByteWriteBuffer h_
+    -- release the buffer if necessary
+    when release $ do
+      -- find size of current buffer
+      old_buf@Buffer{ bufSize=size } <- readIORef haCharBuffer
+      when (sz == size) $ do
+        spare_bufs <- readIORef haBuffers
+        writeIORef haBuffers (BufferListCons raw spare_bufs)
+    -- bb <- readIORef haByteBuffer
+    -- debugIO ("commitBuffer: buffer=" ++ summaryBuffer bb ++ ", handle=" ++ show hdl)
 
 -- backwards compatibility; the text package uses this
 commitBuffer' :: RawCharBuffer -> Int -> Int -> Bool -> Bool -> Handle__
@@ -812,8 +805,8 @@ hPutBuf' handle ptr count can_block
           -- it is set to LineBuffering, be conservative and flush
           -- anyway (we didn't check for newlines in the data).
           case haBufferMode of
-             BlockBuffering _      -> do return ()
-             _line_or_no_buffering -> do flushWriteBuffer h_
+             BlockBuffering _      -> return ()
+             _line_or_no_buffering -> flushWriteBuffer h_
           return r
 
 -- TODO: Possible optimisation:
@@ -842,7 +835,7 @@ bufWrite h_@Handle__{..} ptr !count can_block = do
               else do
                 let offset = bufOffset flushed_buf
                 !bytes <- if can_block
-                            then do writeChunk         h_ (castPtr ptr) offset count
+                            then writeChunk            h_ (castPtr ptr) offset count
                             else writeChunkNonBlocking h_ (castPtr ptr) offset count
                 -- Update buffer with actual bytes written.
                 writeIORef haByteBuffer $! bufferAddOffset bytes flushed_buf
@@ -852,7 +845,7 @@ bufWrite h_@Handle__{..} ptr !count can_block = do
 
 -- Flush the given buffer via the handle, return the flushed buffer
 flushByteWriteBufferGiven :: Handle__ -> Buffer Word8 -> IO (Buffer Word8)
-flushByteWriteBufferGiven h_@Handle__{..} bbuf = do
+flushByteWriteBufferGiven h_@Handle__{..} bbuf =
   if (not (isEmptyBuffer bbuf))
     then do
       bbuf' <- Buffered.flushWriteBuffer haDevice bbuf
@@ -878,7 +871,7 @@ bufferChunk h_@Handle__{..} old_buf@Buffer{ bufRaw=raw, bufR=w, bufSize=size } p
         debugIO "hPutBuf: flushing full buffer after writing"
         _ <- flushByteWriteBufferGiven h_ copied_buf
         return ()
-      else do
+      else
         writeIORef haByteBuffer copied_buf
     return count
 
diff --git a/libraries/base/GHC/TypeLits.hs b/libraries/base/GHC/TypeLits.hs
index 146d24f05b..0cf892f0a0 100644
--- a/libraries/base/GHC/TypeLits.hs
+++ b/libraries/base/GHC/TypeLits.hs
@@ -53,10 +53,9 @@ module GHC.TypeLits
 
   ) where
 
-import GHC.Base(Eq(..), Ord(..), Ordering(..), otherwise)
+import GHC.Base(Eq(..), Ord(..), Ordering(..), String, otherwise)
 import GHC.Types( Nat, Symbol )
 import GHC.Num(Integer, fromInteger)
-import GHC.Base(String)
 import GHC.Show(Show(..))
 import GHC.Read(Read(..))
 import GHC.Real(toInteger)
diff --git a/libraries/base/System/IO.hs b/libraries/base/System/IO.hs
index 03e0e06319..c5dfe057ba 100644
--- a/libraries/base/System/IO.hs
+++ b/libraries/base/System/IO.hs
@@ -368,10 +368,8 @@ appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
 
 -- | The 'readLn' function combines 'getLine' and 'readIO'.
 
-readLn          :: Read a => IO a
-readLn          =  do l <- getLine
-                      r <- readIO l
-                      return r
+readLn :: Read a => IO a
+readLn = getLine >>= readIO
 
 -- | The 'readIO' function is similar to 'read' except that it signals
 -- parse failure to the 'IO' monad instead of terminating the program.
diff --git a/libraries/base/System/Posix/Internals.hs b/libraries/base/System/Posix/Internals.hs
index ea8ddf2173..4bdeabe1bd 100644
--- a/libraries/base/System/Posix/Internals.hs
+++ b/libraries/base/System/Posix/Internals.hs
@@ -95,7 +95,7 @@ fdFileSize fd =
 
 fileType :: FilePath -> IO IODeviceType
 fileType file =
-  allocaBytes sizeof_stat $ \ p_stat -> do
+  allocaBytes sizeof_stat $ \ p_stat ->
   withFilePath file $ \p_file -> do
     throwErrnoIfMinus1Retry_ "fileType" $
       c_stat p_file p_stat
@@ -187,7 +187,7 @@ peekFilePathLen fp = getFileSystemEncoding >>= \enc -> GHC.peekCStringLen enc fp
 #if defined(HTYPE_TCFLAG_T)
 
 setEcho :: FD -> Bool -> IO ()
-setEcho fd on = do
+setEcho fd on =
   tcSetAttr fd $ \ p_tios -> do
     lflag <- c_lflag p_tios :: IO CTcflag
     let new_lflag
@@ -196,7 +196,7 @@ setEcho fd on = do
     poke_c_lflag p_tios (new_lflag :: CTcflag)
 
 getEcho :: FD -> IO Bool
-getEcho fd = do
+getEcho fd =
   tcSetAttr fd $ \ p_tios -> do
     lflag <- c_lflag p_tios :: IO CTcflag
     return ((lflag .&. fromIntegral const_echo) /= 0)
@@ -220,7 +220,7 @@ setCooked fd cooked =
             poke vtime 0
 
 tcSetAttr :: FD -> (Ptr CTermios -> IO a) -> IO a
-tcSetAttr fd fun = do
+tcSetAttr fd fun =
      allocaBytes sizeof_termios  $ \p_tios -> do
         throwErrnoIfMinus1Retry_ "tcSetAttr"
            (c_tcgetattr fd p_tios)
@@ -239,7 +239,7 @@ tcSetAttr fd fun = do
         -- in its terminal flags (try it...).  This function provides a
         -- wrapper which temporarily blocks SIGTTOU around the call, making it
         -- transparent.
-        allocaBytes sizeof_sigset_t $ \ p_sigset -> do
+        allocaBytes sizeof_sigset_t $ \ p_sigset ->
           allocaBytes sizeof_sigset_t $ \ p_old_sigset -> do
              throwErrnoIfMinus1_ "sigemptyset" $
                  c_sigemptyset p_sigset
@@ -339,7 +339,7 @@ setNonBlockingFD _ _ = return ()
 
 #if !defined(mingw32_HOST_OS)
 setCloseOnExec :: FD -> IO ()
-setCloseOnExec fd = do
+setCloseOnExec fd =
   throwErrnoIfMinus1_ "setCloseOnExec" $
     c_fcntl_write fd const_f_setfd const_fd_cloexec
 #endif
diff --git a/libraries/base/Text/ParserCombinators/ReadP.hs b/libraries/base/Text/ParserCombinators/ReadP.hs
index e6dcab55e0..d01dd931c8 100644
--- a/libraries/base/Text/ParserCombinators/ReadP.hs
+++ b/libraries/base/Text/ParserCombinators/ReadP.hs
@@ -278,9 +278,9 @@ string :: String -> ReadP String
 -- ^ Parses and returns the specified string.
 string this = do s <- look; scan this s
  where
-  scan []     _               = do return this
+  scan []     _               = return this
   scan (x:xs) (y:ys) | x == y = do _ <- get; scan xs ys
-  scan _      _               = do pfail
+  scan _      _               = pfail
 
 munch :: (Char -> Bool) -> ReadP String
 -- ^ Parses the first zero or more characters satisfying the predicate.
@@ -291,7 +291,7 @@ munch p =
      scan s
  where
   scan (c:cs) | p c = do _ <- get; s <- scan cs; return (c:s)
-  scan _            = do return ""
+  scan _            = return ""
 
 munch1 :: (Char -> Bool) -> ReadP String
 -- ^ Parses the first one or more characters satisfying the predicate.
@@ -315,7 +315,7 @@ skipSpaces =
      skip s
  where
   skip (c:s) | isSpace c = do _ <- get; skip s
-  skip _                 = do return ()
+  skip _                 = return ()
 
 count :: Int -> ReadP a -> ReadP [a]
 -- ^ @count n p@ parses @n@ occurrences of @p@ in sequence. A list of
diff --git a/libraries/base/Text/Printf.hs b/libraries/base/Text/Printf.hs
index 3aeb0be789..216c29d9e3 100644
--- a/libraries/base/Text/Printf.hs
+++ b/libraries/base/Text/Printf.hs
@@ -292,7 +292,7 @@ instance (a ~ ()) => PrintfType (IO a) where
 
 -- | @since 4.7.0.0
 instance (a ~ ()) => HPrintfType (IO a) where
-    hspr hdl fmts args = do
+    hspr hdl fmts args =
         hPutStr hdl (uprintf fmts (reverse args))
 
 -- | @since 2.01
diff --git a/libraries/base/Text/Read/Lex.hs b/libraries/base/Text/Read/Lex.hs
index 7568f9afaf..7da09164fb 100644
--- a/libraries/base/Text/Read/Lex.hs
+++ b/libraries/base/Text/Read/Lex.hs
@@ -273,7 +273,7 @@ lexCharE =
   do c1 <- get
      if c1 == '\\'
        then do c2 <- lexEsc; return (c2, True)
-       else do return (c1, False)
+       else return (c1, False)
  where
   lexEsc =
     lexEscChar
@@ -341,7 +341,7 @@ lexCharE =
          _    -> pfail
 
   lexAscii =
-    do choice
+     choice
          [ (string "SOH" >> return '\SOH') <++
            (string "SO"  >> return '\SO')
                 -- \SO and \SOH need maximal-munch treatment
@@ -404,9 +404,9 @@ lexString =
     do _ <- char '\\'
        c <- get
        case c of
-         '&'           -> do return ()
+         '&'           -> return ()
          _ | isSpace c -> do skipSpaces; _ <- char '\\'; return ()
-         _             -> do pfail
+         _             -> pfail
 
 -- ---------------------------------------------------------------------------
 --  Lexing numbers
@@ -429,13 +429,14 @@ lexHexOct
 
 lexBaseChar :: ReadP Int
 -- Lex a single character indicating the base; fail if not there
-lexBaseChar = do { c <- get;
-                   case c of
-                        'o' -> return 8
-                        'O' -> return 8
-                        'x' -> return 16
-                        'X' -> return 16
-                        _   -> pfail }
+lexBaseChar = do
+  c <- get
+  case c of
+    'o' -> return 8
+    'O' -> return 8
+    'x' -> return 16
+    'X' -> return 16
+    _   -> pfail
 
 lexDecNumber :: ReadP Lexeme
 lexDecNumber =
@@ -471,8 +472,8 @@ lexDigits base =
  where
   scan (c:cs) f = case valDig base c of
                     Just n  -> do _ <- get; scan cs (f.(n:))
-                    Nothing -> do return (f [])
-  scan []     f = do return (f [])
+                    Nothing -> return (f [])
+  scan []     f = return (f [])
 
 lexInteger :: Base -> ReadP Integer
 lexInteger base =
diff --git a/libraries/base/Unsafe/Coerce.hs b/libraries/base/Unsafe/Coerce.hs
index 0e899ef37a..ea60259ffc 100644
--- a/libraries/base/Unsafe/Coerce.hs
+++ b/libraries/base/Unsafe/Coerce.hs
@@ -9,7 +9,6 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE StandaloneKindSignatures #-}
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE Unsafe #-}
 
diff --git a/libraries/base/tests/Concurrent/MVar001.hs b/libraries/base/tests/Concurrent/MVar001.hs
index 6062cbfa46..0d96a7eb27 100644
--- a/libraries/base/tests/Concurrent/MVar001.hs
+++ b/libraries/base/tests/Concurrent/MVar001.hs
@@ -78,7 +78,7 @@ perform' mv (a:as) =
 
 
 actions :: Gen [Action]
-actions = do
+actions =
   oneof [liftM (NewEmptyMVar:) (actions' True),
          liftM2 (:) (liftM NewMVar arbitrary) (actions' False)]
 
diff --git a/libraries/base/tests/IO/encoding001.hs b/libraries/base/tests/IO/encoding001.hs
index c92f8a3ef5..df3c5f914c 100644
--- a/libraries/base/tests/IO/encoding001.hs
+++ b/libraries/base/tests/IO/encoding001.hs
@@ -33,7 +33,7 @@ main = do
   hClose h
 
   -- convert the UTF-32BE file into each other encoding
-  forM_ encodings $ \(enc,name) -> do
+  forM_ encodings $ \(enc,name) ->
      when (name /=  "utf32be") $ do
        hin <- openFile (file <.> "utf32be") ReadMode
        hSetEncoding hin utf32be
diff --git a/libraries/base/tests/IO/encoding004.hs b/libraries/base/tests/IO/encoding004.hs
index 62ef5d6a93..ffd76191f3 100644
--- a/libraries/base/tests/IO/encoding004.hs
+++ b/libraries/base/tests/IO/encoding004.hs
@@ -58,8 +58,8 @@ main = forM_ [ ("CP936",  2, "CP936",      Just "CP936-UTF8")  -- Representative
         utf8_bs <- BS.readFile ("encoded-data" </> utf8_file <.> "txt")
         Right expected <- decode utf8 utf8_bs
         Right actual   <- decode enc  bs
-        unless (expected == actual) $ do
-            putStrLn (bsDiff 0 actual expected)
+        unless (expected == actual) $
+          putStrLn (bsDiff 0 actual expected)
 
 forTruncations :: BS.ByteString -> (BS.ByteString -> IO a) -> IO [a]
 forTruncations bs f = forSplits bs $ \before _ -> f before
diff --git a/libraries/base/tests/IO/hClose002.hs b/libraries/base/tests/IO/hClose002.hs
index ebf26b4663..20eb0f888a 100644
--- a/libraries/base/tests/IO/hClose002.hs
+++ b/libraries/base/tests/IO/hClose002.hs
@@ -27,6 +27,6 @@ showPossibleException f = do e <- try f
                              print (e :: Either SomeException ())
 
 naughtyClose h = 
-  withHandle_ "naughtyClose" h $ \ Handle__{haDevice=dev} -> do
+  withHandle_ "naughtyClose" h $ \ Handle__{haDevice=dev} ->
      IODevice.close dev
 
diff --git a/libraries/base/tests/IO/hClose003.hs b/libraries/base/tests/IO/hClose003.hs
index cbaf49d6db..6d962fd94e 100644
--- a/libraries/base/tests/IO/hClose003.hs
+++ b/libraries/base/tests/IO/hClose003.hs
@@ -38,5 +38,5 @@ showPossibleException f = do
   sanitise' (x:xs) = if isDigit x then (sanitise' xs) else (x:(sanitise xs))
 
 naughtyClose h = 
-  withHandle_ "naughtyClose" h $ \ Handle__{haDevice=dev} -> do
+  withHandle_ "naughtyClose" h $ \ Handle__{haDevice=dev} ->
      IODevice.close dev
diff --git a/libraries/base/tests/IO/hDuplicateTo001.hs b/libraries/base/tests/IO/hDuplicateTo001.hs
index 99f956a0df..e286235e14 100644
--- a/libraries/base/tests/IO/hDuplicateTo001.hs
+++ b/libraries/base/tests/IO/hDuplicateTo001.hs
@@ -18,7 +18,7 @@ main = do
    putStrLn "bla"
 
 
-getfd h@(FileHandle _ mvar) = do
+getfd h@(FileHandle _ mvar) =
   withMVar mvar $ \h__@Handle__{haDevice=dev} ->
    case cast dev of
      Just fd -> return (FD.fdFD fd)
diff --git a/libraries/base/tests/IO/hReady002.hs b/libraries/base/tests/IO/hReady002.hs
index b8b648065b..b13ef8911e 100644
--- a/libraries/base/tests/IO/hReady002.hs
+++ b/libraries/base/tests/IO/hReady002.hs
@@ -5,6 +5,6 @@ import System.Exit
 
 main = do
   m <- newEmptyMVar
-  forkIO $ do threadDelay 500000; putMVar m Nothing
-  forkIO $ do hReady stdin >>= putMVar m . Just
+  forkIO $ threadDelay 500000 >> putMVar m Nothing
+  forkIO $ hReady stdin >>= putMVar m . Just
   takeMVar m >>= print
diff --git a/libraries/base/tests/IO/newline001.hs b/libraries/base/tests/IO/newline001.hs
index 3da867509f..1c894422a9 100644
--- a/libraries/base/tests/IO/newline001.hs
+++ b/libraries/base/tests/IO/newline001.hs
@@ -101,7 +101,7 @@ testoutput b = do
   check "out2" b (toCRLF content) str
   hClose h
 
-check s b str1 str2 = do
+check s b str1 str2 =
   when (str1 /= str2) $ error ("failed: " ++ s ++ ", " ++ show b ++ '\n':show str1 ++ '\n':show str2)
 
 read_chars :: Handle -> IO String
diff --git a/libraries/base/tests/IO/readwrite002.hs b/libraries/base/tests/IO/readwrite002.hs
index 37c7da39cb..5795525b2c 100644
--- a/libraries/base/tests/IO/readwrite002.hs
+++ b/libraries/base/tests/IO/readwrite002.hs
@@ -29,7 +29,6 @@ main = do
    hSeek cd AbsoluteSeek 0
    hSetBuffering cd LineBuffering
    speak cd  `catchIOError` \ err -> if isEOFError err then putStrLn "\nCaught EOF" else ioError err
-   return ()
    hSeek cd AbsoluteSeek 0
    hSetBuffering cd (BlockBuffering Nothing)
    speak cd  `catchIOError` \ err -> if isEOFError err then putStrLn "\nCaught EOF" else ioError err
diff --git a/libraries/base/tests/T13167.hs b/libraries/base/tests/T13167.hs
index e41104cde9..d8808667b1 100644
--- a/libraries/base/tests/T13167.hs
+++ b/libraries/base/tests/T13167.hs
@@ -25,5 +25,5 @@ run = do
 quit :: MVar () -> IO ()
 quit m = do
   ref <- newIORef ()
-  void $ mkWeakIORef ref $ do
+  void $ mkWeakIORef ref $
     putMVar m ()
diff --git a/libraries/base/tests/T13896.hs b/libraries/base/tests/T13896.hs
index 9e269a4a7c..8b4c47f44a 100644
--- a/libraries/base/tests/T13896.hs
+++ b/libraries/base/tests/T13896.hs
@@ -65,11 +65,11 @@ main = do
   -- without escaping everything inside
 
   (filter (not . null) $
-   unescapeArgs "this\\ is\\ 'not escape\\d \"inside\"'\\ yo\n")
-   `assertEqual`
-   ["this is not escaped \"inside\" yo"]
+    unescapeArgs "this\\ is\\ 'not escape\\d \"inside\"'\\ yo\n")
+    `assertEqual`
+    ["this is not escaped \"inside\" yo"]
 
   (filter (not . null) $
-   unescapeArgs "this\\ is\\ \"not escape\\d 'inside'\"\\ yo\n")
-   `assertEqual`
-   ["this is not escaped 'inside' yo"]
+    unescapeArgs "this\\ is\\ \"not escape\\d 'inside'\"\\ yo\n")
+    `assertEqual`
+    ["this is not escaped 'inside' yo"]
diff --git a/libraries/base/tests/T9532.hs b/libraries/base/tests/T9532.hs
index e99a42b572..b9f280fcf8 100644
--- a/libraries/base/tests/T9532.hs
+++ b/libraries/base/tests/T9532.hs
@@ -68,7 +68,7 @@ main = do
 
     -- Compare impl-under-test with reference-impl
     checkCLZ :: (Typeable a, Show a, Integral a, FiniteBits a) => a -> IO ()
-    checkCLZ v = unless (vri == viut) $ do
+    checkCLZ v = unless (vri == viut) $
         putStrLn $ concat [ "FAILED: clz (0x", showHex v " :: ", tyName
                           , ") ==> (RI=", show vri, " vs. IUT=", show viut, ")"
                           ]
@@ -79,7 +79,7 @@ main = do
 
     -- Compare impl-under-test with reference-impl
     checkCTZ :: (Typeable a, Show a, Integral a, FiniteBits a) => a -> IO ()
-    checkCTZ v = unless (vri == viut) $ do
+    checkCTZ v = unless (vri == viut) $
         putStrLn $ concat [ "FAILED: ctz (0x", showHex v " :: ", tyName
                           , ") ==> (RI=", show vri, " vs. IUT=", show viut, ")"
                           ]
diff --git a/libraries/base/tests/foldableArray.hs b/libraries/base/tests/foldableArray.hs
index 92217d73d2..5caf4eeb76 100644
--- a/libraries/base/tests/foldableArray.hs
+++ b/libraries/base/tests/foldableArray.hs
@@ -6,7 +6,6 @@ module Main where
 
 import Prelude hiding (foldr, foldl, foldl', foldr1, foldl1, length, null, sum,
                        product, all, any, and, or)
-import Data.Foldable
 import Control.Exception
 import Data.Array
 import Data.Foldable
diff --git a/libraries/base/tests/qsem001.hs b/libraries/base/tests/qsem001.hs
index 0088c6e989..4254c2b9fc 100644
--- a/libraries/base/tests/qsem001.hs
+++ b/libraries/base/tests/qsem001.hs
@@ -68,7 +68,7 @@ sem_fifo = do
 sem_kill :: Assertion
 sem_kill  = do
   q <- new 0
-  t <- forkIO $ do wait q
+  t <- forkIO $ wait q
   threadDelay 100000
   killThread t
   m <- newEmptyMVar
@@ -80,8 +80,8 @@ sem_kill  = do
 sem_bracket :: Assertion
 sem_bracket = do
   q <- new 1
-  ts <- forM [1..100000] $ \n -> do
-     forkIO $ do bracket_ (wait q) (signal q) (return ())
+  ts <- forM [1..100000] $ \n ->
+     forkIO $ bracket_ (wait q) (signal q) (return ())
   mapM_ killThread ts
   wait q
 
diff --git a/libraries/base/tests/qsemn001.hs b/libraries/base/tests/qsemn001.hs
index c61d2896c2..3f76f376aa 100644
--- a/libraries/base/tests/qsemn001.hs
+++ b/libraries/base/tests/qsemn001.hs
@@ -92,7 +92,7 @@ semn3 = do
 semn_kill :: Assertion
 semn_kill  = do
   q <- new 0
-  t <- forkIO $ do wait q 1
+  t <- forkIO $ wait q 1
   threadDelay 10000
   killThread t
   m <- newEmptyMVar
@@ -103,7 +103,7 @@ semn_kill  = do
 sem_bracket :: Assertion
 sem_bracket = do
   q <- new 1
-  ts <- forM [1..100000] $ \n -> do
-     forkIO $ do bracket_ (wait q 1) (signal q 1) (return ())
+  ts <- forM [1..100000] $ \n ->
+     forkIO $ bracket_ (wait q 1) (signal q 1) (return ())
   mapM_ killThread ts
   wait q 1