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

2 files changed, 7 insertions, 4 deletions

diff --git a/utils/ghc-pkg/Main.hs b/utils/ghc-pkg/Main.hs
index 7bc14094d1..5e91d905e6 100644
--- a/utils/ghc-pkg/Main.hs
+++ b/utils/ghc-pkg/Main.hs
@@ -390,7 +390,7 @@ runit verbosity cli nonopts = do
 
         splitFields fields = unfoldr splitComma (',':fields)
           where splitComma "" = Nothing
-                splitComma fs = Just $ break (==',') (tail fs)
+                splitComma (_ : fs) = Just $ break (==',') fs
 
         -- | Parses a glob into a predicate which tests if a string matches
         -- the glob.  Returns Nothing if the string in question is not a glob.
@@ -1962,10 +1962,11 @@ checkUnitId ipi db_stack update = do
 
 checkDuplicates :: PackageDBStack -> InstalledPackageInfo
                 -> Bool -> Bool-> Validate ()
-checkDuplicates db_stack pkg multi_instance update = do
+checkDuplicates [] _ _ _ = pure ()
+checkDuplicates (hd : _) pkg multi_instance update = do
   let
         pkgid = mungedId pkg
-        pkgs  = packages (head db_stack)
+        pkgs  = packages hd
   --
   -- Check whether this package id already exists in this DB
   --
diff --git a/utils/hpc/HpcUtils.hs b/utils/hpc/HpcUtils.hs
index da62f4a364..a5d93fccce 100644
--- a/utils/hpc/HpcUtils.hs
+++ b/utils/hpc/HpcUtils.hs
@@ -13,8 +13,10 @@ dropWhileEndLE p = foldr (\x r -> if null r && p x then [] else x:r) []
 grabHpcPos :: Map.Map Int String -> HpcPos -> String
 grabHpcPos hsMap srcspan = 
          case lns of
+           [] -> error "grabHpcPos: invalid source span"
            [ln] -> (take ((c2 - c1) + 1) $ drop (c1 - 1) ln)
-           _ -> let lns1 = drop (c1 -1) (head lns) : tail lns
+           hd : tl ->
+                let lns1 = drop (c1 -1) hd : tl
                     lns2 = init lns1 ++ [take (c2 + 1) (last lns1) ]
                  in foldl1 (\ xs ys -> xs ++ "\n" ++ ys) lns2
   where (l1,c1,l2,c2) = fromHpcPos srcspan