Assorted changes to avoid Data.List.{head,tail}

5 files changed, 14 insertions, 12 deletions

diff --git a/utils/check-exact/ExactPrint.hs b/utils/check-exact/ExactPrint.hs
index be7bb54c0d..a569b803d4 100644
--- a/utils/check-exact/ExactPrint.hs
+++ b/utils/check-exact/ExactPrint.hs
@@ -3696,12 +3696,13 @@ exactVanillaDeclHead :: (Monad m, Monoid w)
 exactVanillaDeclHead thing tvs@(HsQTvs { hsq_explicit = tyvars }) fixity context = do
   let
     exact_tyvars (varl:varsr)
-      | fixity == Infix && length varsr > 1 = do
+      | hvarsr : tvarsr@(_ : _) <- varsr
+      , fixity == Infix = do
           varl' <- markAnnotated varl
           thing' <- markAnnotated thing
-          hvarsr <- markAnnotated (head varsr)
-          tvarsr <- markAnnotated (tail varsr)
-          return (thing', varl':hvarsr:tvarsr)
+          hvarsr' <- markAnnotated hvarsr
+          tvarsr' <- markAnnotated tvarsr
+          return (thing', varl':hvarsr':tvarsr')
       | fixity == Infix = do
           varl' <- markAnnotated varl
           thing' <- markAnnotated thing
diff --git a/utils/check-exact/Main.hs b/utils/check-exact/Main.hs
index c4eedde74a..74525dd5f9 100644
--- a/utils/check-exact/Main.hs
+++ b/utils/check-exact/Main.hs
@@ -577,11 +577,11 @@ changeWhereIn3b :: Changer
 changeWhereIn3b _libdir (L l p) = do
   let decls0 = hsmodDecls p
       (decls,_,w) = runTransform (balanceCommentsList decls0)
-      (de0:_:de1:d2:_) = decls
+      (de0:tdecls@(_:de1:d2:_)) = decls
       de0' = setEntryDP de0 (DifferentLine 2 0)
       de1' = setEntryDP de1 (DifferentLine 2 0)
       d2' = setEntryDP d2 (DifferentLine 2 0)
-      decls' = d2':de1':de0':(tail decls)
+      decls' = d2':de1':de0':tdecls
   debugM $ unlines w
   debugM $ "changeWhereIn3b:de1':" ++ showAst de1'
   let p2 = p { hsmodDecls = decls'}
@@ -799,8 +799,9 @@ rmDecl5 _libdir lp = do
           go :: HsExpr GhcPs -> Transform (HsExpr GhcPs)
           go (HsLet a tkLet lb tkIn expr) = do
             decs <- hsDeclsValBinds lb
+            let hdecs : _ = decs
             let dec = last decs
-            _ <- transferEntryDP (head decs) dec
+            _ <- transferEntryDP hdecs dec
             lb' <- replaceDeclsValbinds WithoutWhere lb [dec]
             return (HsLet a tkLet lb' tkIn expr)
           go x = return x
diff --git a/utils/check-exact/Preprocess.hs b/utils/check-exact/Preprocess.hs
index 756dc18984..55d84763f5 100644
--- a/utils/check-exact/Preprocess.hs
+++ b/utils/check-exact/Preprocess.hs
@@ -192,7 +192,7 @@ stripPreprocessorDirectives :: GHC.StringBuffer -> GHC.StringBuffer
 stripPreprocessorDirectives buf = buf'
   where
     srcByLine = lines $ sbufToString buf
-    noDirectivesLines = map (\line -> if line /= [] && head line == '#' then "" else line) srcByLine
+    noDirectivesLines = map (\line -> case line of '#' : _ -> ""; _ -> line) srcByLine
     buf' = GHC.stringToStringBuffer $ unlines noDirectivesLines
 
 -- ---------------------------------------------------------------------
@@ -259,7 +259,7 @@ fingerprintStrings ss = GHC.fingerprintFingerprints $ map GHC.fingerprintString
 getPreprocessorAsComments :: FilePath -> IO [(GHC.Located GHC.Token, String)]
 getPreprocessorAsComments srcFile = do
   fcontents <- readFileGhc srcFile
-  let directives = filter (\(_lineNum,line) -> line /= [] && head line == '#')
+  let directives = filter (\(_lineNum,line) -> case line of '#' : _ -> True; _ -> False)
                     $ zip [1..] (lines fcontents)
 
   let mkTok (lineNum,line) = (GHC.L l (GHC.ITlineComment line (makeBufSpan l)),line)
diff --git a/utils/check-exact/Transform.hs b/utils/check-exact/Transform.hs
index 3e3ebdcb39..45f3612a76 100644
--- a/utils/check-exact/Transform.hs
+++ b/utils/check-exact/Transform.hs
@@ -322,7 +322,7 @@ setEntryDP (L (SrcSpanAnn (EpAnn (Anchor r _) an cs) l) a) dp
                l) a
               where
                 cs'' = setPriorComments cs (L (Anchor (anchor ca) (MovedAnchor dp)) c:cs')
-                lc = head $ reverse $ (L ca c:cs')
+                lc = last $ (L ca c:cs')
                 delta = tweakDelta $ ss2delta (ss2pos $ anchor $ getLoc lc) r
                 line = getDeltaLine delta
                 col = deltaColumn delta
diff --git a/utils/check-exact/Utils.hs b/utils/check-exact/Utils.hs
index b60c989bcf..14a05a2337 100644
--- a/utils/check-exact/Utils.hs
+++ b/utils/check-exact/Utils.hs
@@ -458,8 +458,8 @@ glast  info []    = error $ "glast " ++ info ++ " []"
 glast _info h     = last h
 
 gtail :: String -> [a] -> [a]
-gtail  info []   = error $ "gtail " ++ info ++ " []"
-gtail _info h    = tail h
+gtail  info []    = error $ "gtail " ++ info ++ " []"
+gtail _info (_:t) = t
 
 gfromJust :: String -> Maybe a -> a
 gfromJust _info (Just h) = h