fix a few GHC 9.8 warnings

src/Diagrams/CubicSpline/Internal.hs

@@ -50,12 +50,14 @@ solveCubicSplineDerivativesClosed xs = solveCyclicTriDiagonal as bs as ds 1 1
 solveCubicSplineCoefficients :: Fractional a => Bool -> [a] -> [[a]]
 solveCubicSplineCoefficients closed xs =
     [ [x,d,3*(x1-x)-2*d-d1,2*(x-x1)+d+d1]
-    | (x,x1,d,d1) <- zip4 xs' (tail xs') ds' (tail ds')
+    | (x,x1,d,d1) <- zip4 xs' (drop 1 xs') ds' (drop 1 ds')
     ]
   where
     ds | closed    = solveCubicSplineDerivativesClosed xs
        | otherwise = solveCubicSplineDerivatives xs
-    close as | closed    = as ++ [head as]
-             | otherwise = as
+    close [] = []
+    close as@(a:_)
+      | closed    = as ++ [a]
+      | otherwise = as
     xs' = close xs
     ds' = close ds

src/Diagrams/TwoD/Points.hs

@@ -24,16 +24,16 @@ import Linear.Affine
 
 -- | Find the convex hull of a list of points using Andrew's monotone chain
 --   algorithm O(n log n).
---   
+--
 --   Returns clockwise list of points starting from the left-most point.
 convexHull2D :: OrderedField n => [P2 n] -> [P2 n]
-convexHull2D ps = init upper ++ reverse (tail lower)
+convexHull2D ps = init upper ++ reverse (drop 1 lower)
   where
     (upper, lower) = sortedConvexHull (sort ps)
 
--- | Find the convex hull of a set of points already sorted in the x direction. 
---   The first list of the tuple is the upper hull going clockwise from 
---   left-most to right-most point. The second is the lower hull from 
+-- | Find the convex hull of a set of points already sorted in the x direction.
+--   The first list of the tuple is the upper hull going clockwise from
+--   left-most to right-most point. The second is the lower hull from
 --   right-most to left-most in the anti-clockwise direction.
 sortedConvexHull :: OrderedField n => [P2 n] -> ([P2 n], [P2 n])
 sortedConvexHull ps = (chain True ps, chain False ps)