Fix ghc warnings

Day2/puzzle1.hs

@@ -1,10 +1,11 @@
-import Data.List (sort)
+import Data.List (sort, sortBy)
+import Data.Ord
 
 isSafe :: [Int] -> Bool
 isSafe xs = (isAscending xs || isDescending xs) && maximum distances <= 3 && minimum distances >= 1
             where isAscending xs  = xs == sort xs
-                  isDescending xs = xs == reverse (sort xs)
-                  distances       = map abs $ zipWith (-) xs (tail xs)
+                  isDescending xs = xs == sortBy (comparing Down) xs
+                  distances       = map abs $ zipWith (-) xs (drop 1 xs)
 
 main = do
     contents <- lines <$> readFile "day2.txt"

Day2/puzzle2.hs

@@ -1,15 +1,16 @@
-import Data.List (sort, inits, tails)
+import Data.List (sort, sortBy, inits, tails)
+import Data.Ord
 
 isSafe :: [Int] -> Bool
 isSafe xs = (isAscending xs || isDescending xs) && maximum distances <= 3 && minimum distances >= 1
             where isAscending xs  = xs == sort xs
-                  isDescending xs = xs == reverse (sort xs)
-                  distances       = map abs $ zipWith (-) xs (tail xs)
+                  isDescending xs = xs == sortBy (comparing Down) xs
+                  distances       = map abs $ zipWith (-) xs (drop 1 xs)
 
 removeLevel :: [Int] -> [[Int]]
 removeLevel xs = zipWith (++) ys zs
-            where ys = map init $ tail (inits xs)
-                  zs = map tail $ init (tails xs)
+            where ys = map init $ drop 1 (inits xs)
+                  zs = map (drop 1) $ init (tails xs)
 
 main = do
     contents <- lines <$> readFile "day2.txt"