1 files changed, 74 insertions, 0 deletions
diff --git a/2020/04-Passport_Processing/first.hs b/2020/04-Passport_Processing/first.hs
new file mode 100644
index 0000000..9993f29
--- /dev/null
+++ b/2020/04-Passport_Processing/first.hs
@@ -0,0 +1,74 @@
+-- requires cabal install --lib megaparsec parser-combinators
+module Main (main) where
+
+import Control.Applicative.Permutations
+import Control.Monad (void, when)
+import Data.Maybe (catMaybes)
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import System.Exit (die)
+
+exampleExpectedOutput = 2
+
+data Passport = Passport { byr :: String
+                         , iyr :: String
+                         , eyr :: String
+                         , hgt :: String
+                         , hcl :: String
+                         , ecl :: String
+                         , pid :: String
+                         } deriving (Show)
+
+type Parser = Parsec Void String
+
+parseString :: String -> Parser String
+parseString key = do
+  void $ string key
+  void $ char ':'
+  void (optional $ char '#')
+  some alphaNumChar
+
+spaces = char ' ' <|> char '\n'
+
+parsePassport :: Parser (Maybe Passport)
+parsePassport = do
+  (byr, iyr, eyr, hgt, hcl, ecl, pid, cid) <- runPermutation $
+    (,,,,,,,) <$> toPermutationWithDefault Nothing (Just <$> parseString "byr" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "iyr" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "eyr" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "hgt" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "hcl" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "ecl" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "pid" <* spaces)
+              <*> toPermutationWithDefault Nothing (Just <$> parseString "cid" <* spaces)
+  void (char '\n')
+  return $ makePassport byr iyr eyr hgt hcl ecl pid cid
+
+makePassport :: Maybe String -> Maybe String -> Maybe String -> Maybe String -> Maybe String -> Maybe String -> Maybe String -> Maybe String -> Maybe Passport
+makePassport (Just byr) ( Just iyr) (Just eyr) (Just hgt) (Just hcl) (Just ecl) (Just pid) _ = Just $ Passport { byr=byr, iyr=iyr, eyr=eyr, hgt=hgt, hcl=hcl, ecl=ecl, pid=pid }
+makePassport _ _ _ _ _ _ _ _ = Nothing
+
+parsePassports :: Parser [Passport]
+parsePassports = do
+  passports <- some (parsePassport)
+  eof
+  return $ catMaybes passports
+
+parseInput :: String -> IO [Passport]
+parseInput filename = do
+  input <- readFile filename
+  case runParser parsePassports filename input of
+    Left bundle -> die $ errorBundlePretty bundle
+    Right passports -> return passports
+
+compute :: [Passport]-> Int
+compute passports = length passports
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input