improve code

4.hs

@@ -6,49 +6,23 @@ import Data.List
 import Data.List.Extra (stripSuffix)
 import Data.List.Split
 import Data.Maybe
-import Debug.Trace
 import Text.Read
+import Data.Set (Set, fromList, isSubsetOf)
 
-data Attr
-    = Byr
-    | Iyr
-    | Eyr
-    | Hgt
-    | Hcl
-    | Ecl
-    | Pid
-    | Cid
+data Attr = Byr | Iyr | Eyr | Hgt | Hcl | Ecl | Pid | Cid 
     deriving (Show, Bounded, Enum, Eq, Ord)
 
-type Passport = [Attr]
-
-intval :: (Int, Int) -> Int -> Maybe Int
-intval (lo, hi) = \n ->
-    if n >= lo && n <= hi then Just n
-    else Nothing
+intval :: Int -> Int -> Int -> Maybe Int
+intval lo hi n = guard (n >= lo && n <= hi) $> n
 
 nDigits :: Int -> String -> Maybe String
-nDigits n = \s ->
-    if length s == n && all isDigit s then Just s
-    else Nothing
+nDigits n s = guard (length s == n && all isDigit s) $> s
 
 hexColor :: String -> Maybe String
-hexColor s =
-    if length s == 7
-        && s !! 0 == '#'
-        && all (\c -> elem c "0123456789abcdef") (drop 1 s) then Just s
-    else Nothing
+hexColor s = guard (length s == 7 && s !! 0 == '#' && all (\c -> elem c "0123456789abcdef") (drop 1 s)) $> s
 
 validEcl :: String -> Bool
-validEcl s = case s of
-    "amb" -> True
-    "blu" -> True
-    "brn" -> True
-    "gry" -> True
-    "grn" -> True
-    "hzl" -> True
-    "oth" -> True
-    _ -> False
+validEcl = flip elem ["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]
 
 parseAttr :: String -> Maybe Attr
 parseAttr s =
@@ -56,13 +30,13 @@ parseAttr s =
     let key = parts !! 0 in
     let value = parts !! 1 in
     case key of
-        "byr" -> (readMaybe value >>= intval (1920, 2002)) $> Byr
-        "iyr" -> (readMaybe value >>= intval (2010, 2020)) $> Iyr
-        "eyr" -> (readMaybe value >>= intval (2020, 2030)) $> Eyr
+        "byr" -> (readMaybe value >>= intval 1920 2002) $> Byr
+        "iyr" -> (readMaybe value >>= intval 2010 2020) $> Iyr
+        "eyr" -> (readMaybe value >>= intval 2020 2030) $> Eyr
         "hgt" ->
-            ((stripSuffix "cm" value >>= readMaybe >>= intval (150, 193)) <|>
-            (stripSuffix "in" value >>= readMaybe >>= intval(59, 76)))
-            $> Hgt
+            let inch = stripSuffix "cm" value >>= readMaybe >>= intval 150 193 in
+            let cm = stripSuffix "in" value >>= readMaybe >>= intval 59 76 in
+            (inch <|> cm) $> Hgt
         "hcl" -> hexColor value $> Hcl
         "ecl" -> if validEcl value then Just Ecl else Nothing
         "pid" -> nDigits 9 value $> Pid
@@ -70,28 +44,25 @@ parseAttr s =
         _ -> Nothing
 
 processLine :: String -> Maybe [Attr]
-processLine line = sequence $ (map parseAttr $ splitOn " " line)
+processLine = mapM parseAttr . splitOn " "
 
-requiredAttrs :: [Attr]
-requiredAttrs = enumFromTo Byr Pid
+requiredAttrs :: Set Attr
+requiredAttrs = fromList $ enumFromTo Byr Pid
 
-combineAttrs :: [Attr] -> Maybe Passport
-combineAttrs attrs =
-    let intersection = intersect attrs requiredAttrs in
-    if sort intersection == sort requiredAttrs then Just attrs
-    else Nothing
+combineAttrs :: [Attr] -> Maybe [Attr]
+combineAttrs attrs = guard (isSubsetOf requiredAttrs $ fromList $ attrs) $> attrs
 
-processPassport :: [String] -> Maybe Passport
-processPassport lines = concat <$> (sequence $ map processLine lines) >>= combineAttrs
+processPassport :: [String] -> Maybe [Attr]
+processPassport = combineAttrs . concat <=< mapM processLine
 
-processLines :: [String] -> [Maybe Passport]
-processLines lines = map processPassport $ splitWhen (== "") lines
+processLines :: [String] -> [Maybe [Attr]]
+processLines = map processPassport . splitWhen (== "")
 
-countValid :: [Maybe Passport] -> Int
+countValid :: [Maybe [Attr]] -> Int
 countValid = length . filter isJust
 
 main :: IO ()
 main = do
     content <- readFile "4.txt"
     let valid = countValid $ processLines $ lines content
-    putStrLn (show valid)
+    print valid