diff --git a/common/AoC.hs b/common/AoC.hs
new file mode 100644
index 0000000..b687673
--- /dev/null
+++ b/common/AoC.hs
@@ -0,0 +1,11 @@
+module AoC where
+
+(.:) :: (c -> d) -> (a -> b -> c) -> a -> b -> d
+f .: g = (f .) . g
+infixl 8 .:
+
+runAoC :: (Show r1, Show r2) => (String -> i) -> (i -> r1) -> (i -> r2) -> IO ()
+runAoC inputTransform part1 part2 = do
+    contents <- inputTransform <$> getContents
+    print $ part1 contents
+    print $ part2 contents
diff --git a/day1/day1.hs b/day1/day1.hs
index 643ff82..6a7ebcf 100644
--- a/day1/day1.hs
+++ b/day1/day1.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE TypeApplications #-}
+import AoC
 
 import Data.List
 import Data.Maybe
@@ -7,6 +7,5 @@ import Control.Monad
 find_n_summing :: (Num a, Eq a) => a -> Int -> [a] -> Maybe [a]
 find_n_summing to = (find ((to ==) . sum) .) . replicateM
 
-main = do
-    nums <- fmap read <$> lines <$> readFile "input.txt"
-    mapM_ print $ product <$> fromJust <$> flip (find_n_summing 2020) nums <$> [2, 3]
+main = runAoC (fmap read <$> lines) (solution 2) (solution 3)
+    where solution = product . fromJust .: find_n_summing 2020
diff --git a/day3/day3.hs b/day3/day3.hs
index 53dfa13..113a837 100644
--- a/day3/day3.hs
+++ b/day3/day3.hs
@@ -1,3 +1,5 @@
+import AoC
+
 import Control.Applicative (empty)
 import Control.Monad.Zip (mzip)
 import Data.List (intercalate)
@@ -6,9 +8,8 @@ import Data.Maybe (catMaybes)
 compose2 :: (a' -> b' -> c) -> (a -> a') -> (b -> b') -> a -> b -> c
 compose2 f g h x y = f (g x) (h y)
 
-(.:) :: (c -> d) -> (a -> b -> c) -> a -> b -> d
-f .: g = (f .) . g
-infixl 8 .:
+(??) :: Functor f => f (a -> b) -> a -> f b
+f ?? x = fmap ($ x) f
 
 countHits :: (Int, Int) -> [[Bool]] -> Int
 countHits = length . filterMap lookup . catMaybes .: compose2 (zipWith mzip) maybeIndices justLines
@@ -22,8 +23,6 @@ countHits = length . filterMap lookup . catMaybes .: compose2 (zipWith mzip) may
 treeCharToBool :: Char -> Bool
 treeCharToBool = (== '#')
 
-main = do
-    charLines <- lines <$> readFile "input.txt"
-    let boolLines = cycle <$> map treeCharToBool <$> charLines
-    print $ countHits (3, 1) boolLines
-    print $ product $ flip countHits boolLines <$> [(1,1), (3,1), (5,1), (7,1), (1,2)]
+main = runAoC (fmap (cycle . map treeCharToBool) <$> lines) part1 part2
+    where part1 = countHits (3, 1)
+          part2 = product . (fmap countHits [(1,1), (3,1), (5,1), (7,1), (1,2)] ??)
diff --git a/day4/day4.hs b/day4/day4.hs
index 558beda..b2baa8a 100644
--- a/day4/day4.hs
+++ b/day4/day4.hs
@@ -1,3 +1,5 @@
+import AoC
+
 import Control.Applicative ((<|>))
 import Control.Monad (guard, mfilter)
 import Data.Char (isDigit)
@@ -39,10 +41,6 @@ fieldSpecs = [ ("byr", BirthYear <$> parseYearIn 1920 2002)
     where parseYearIn = flip mfilter (parseNumber 4) .: within
           parseHexDigit = choice . map char $ ['0'..'9']++['a'..'f']
 
-(.:) :: (c -> d) -> (a -> b -> c) -> a -> b -> d
-f .: g = (f .) . g
-infixl 8 .:
-
 within :: Ord a => a -> a -> a -> Bool
 within a b x = a <= x && x <= b
 
@@ -92,7 +90,7 @@ parsePassport :: ReadP [Field]
 parsePassport = spaceSeparated parseField
 
 oneCompleteResult :: ReadP a -> String -> Maybe a
-oneCompleteResult p s = case readP_to_S p s of
+oneCompleteResult p s = case readP_to_S (p <* eof) s of
                           [(x, "")] -> Just x
                           _ -> Nothing
 
@@ -103,13 +101,6 @@ hasAllRequiredFields :: String -> Bool
 hasAllRequiredFields = maybe False containsAllFields . fieldNames
     where requiredFieldNames = ["byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"]
           containsAllFields fields = all (`elem` fields) requiredFieldNames
-          fieldNames = oneCompleteResult (parseFieldNames <* eof)
+          fieldNames = oneCompleteResult parseFieldNames
 
-main = do
-    batches <- splitOnEmptyLines <$> readFile "input.txt"
-
-    let withRequiredFields = filter hasAllRequiredFields batches
-    print $ length withRequiredFields
-
-    let passports = mapMaybe (oneCompleteResult (parsePassport <* eof)) withRequiredFields
-    print $ length passports
+main = runAoC (filter hasAllRequiredFields . splitOnEmptyLines) (length) (length . mapMaybe (oneCompleteResult parsePassport))