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diff --git a/2020/04b.hs b/2020/04b.hs
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+module Day4a where
+
+import System.Environment (getArgs)
+import Data.List.Split (splitOn)
+
+-- Split a passport declaration into k:v declarations
+getDeclarations :: String -> [String]
+getDeclarations xs = concat [splitOn "\n" y | y <- splitOn " " xs]
+
+-- Split a passport declaration into tuples of (key, value)
+getTuples :: String -> [(String, String)]
+getTuples xs = [(head x, x!!1) | x <- map (splitOn ":") $ getDeclarations xs]
+
+-- Check a passport is valid
+passportValid :: String -> Bool
+passportValid xs = and [r `elem` map fst tups | (r, _) <- reqs] && -- Contains all required fields
+                   and [f v | (k, v) <- tups, (t, f) <- reqs, t == k] -- Passes validation rules
+        where tups = getTuples xs
+              reqs = [("byr", numberValid 4 1920 2002),
+                      ("iyr", numberValid 4 2010 2020),
+                      ("eyr", numberValid 4 2020 2030),
+                      ("hgt", heightValid),
+                      ("hcl", hexClValid),
+                      ("ecl", enumValid ["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]),
+                      ("pid", numberValid 9 0 999999999)]
+
+-- Validation functions
+
+-- digits, low, high, value
+numberValid :: Int -> Int -> Int -> String -> Bool
+(numberValid d l h) x = length x == d && val >= l && val <= h
+                where val = read x 
+
+heightValid :: String -> Bool
+heightValid x | u == "cm" = v >= 150 && v <= 193
+              | u == "in" = v >= 59 && v <= 76
+              | otherwise = False
+                where u = drop (length x - 2) x
+                      v = read $ take (length x - 2) x :: Int
+
+enumValid :: [String] -> String -> Bool
+(enumValid e) x = x `elem` e
+
+hexClValid :: String -> Bool
+hexClValid ('#':ds) = and [x `elem` "abcdef0123456789" | x <- ds] && length ds == 6
+hexClValid _ = False
+
+-- Usage: runghc --ghc-arg="-package split" 4b.hs inputs/day4
+main :: IO ()
+main = do 
+        args <- getArgs;
+        content <- readFile $ head args;
+
+        let ps = splitOn "\n\n" content;
+        let valid = filter passportValid ps;
+
+        print $ length valid;
+        return ();
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