Solve day 4, part 1

AdventOfCode2020.cabal

@@ -17,7 +17,7 @@ maintainer:          gael@depreeuw.dev
 extra-source-files:  CHANGELOG.md, README.md
 
 library
-  exposed-modules:     Day1, Day2, Day3
+  exposed-modules:     Day1, Day2, Day3, Day4
   -- other-modules:
   -- other-extensions:
   build-depends:       base ^>=4.13.0.0

Main.hs

@@ -3,9 +3,11 @@ module Main where
 import Day1 (day1)
 import Day2 (day2)
 import Day3 (day3)
+import Day4 (day4)
 
 main :: IO ()
 main = do
   day1
   day2
   day3
+  day4

src/Day4.hs

@@ -0,0 +1,75 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Day4 (day4) where
+
+import Control.Applicative ((<|>))
+import Control.Monad (void)
+import qualified Data.Attoparsec.Text as P
+import qualified Data.Map as M
+import Data.Maybe (catMaybes)
+import qualified Data.Text as T
+
+type BYR = T.Text
+
+type IYR = T.Text
+
+type EYR = T.Text
+
+type HGT = T.Text
+
+type HCL = T.Text
+
+type ECL = T.Text
+
+type PID = T.Text
+
+type CID = T.Text
+
+data Passport = ValidPassport
+  { byr :: BYR,
+    iyr :: IYR,
+    eyr :: EYR,
+    hgt :: HGT,
+    hcl :: HCL,
+    ecl :: ECL,
+    pid :: PID,
+    cid :: Maybe CID -- Definitely not a hack!
+  }
+  deriving (Eq, Show)
+
+parserPair :: P.Parser (T.Text, T.Text)
+parserPair = do
+  key <- P.count 3 P.letter
+  _ <- P.char ':'
+  value <- P.takeWhile1 (P.inClass "a-zA-Z0-9#")
+  return (T.pack key, value)
+
+parserEntry :: P.Parser (M.Map T.Text T.Text)
+parserEntry = M.fromList <$> parserPair `P.sepBy` (void P.space <|> P.endOfLine)
+
+fromMap :: M.Map T.Text T.Text -> Maybe Passport
+fromMap m = do
+  byr <- m M.!? "byr"
+  iyr <- m M.!? "iyr"
+  eyr <- m M.!? "eyr"
+  hgt <- m M.!? "hgt"
+  hcl <- m M.!? "hcl"
+  ecl <- m M.!? "ecl"
+  pid <- m M.!? "pid"
+  return $ ValidPassport byr iyr eyr hgt hcl ecl pid (m M.!? "cid")
+
+parserPassport :: P.Parser (Maybe Passport)
+parserPassport = fromMap <$> parserEntry
+
+parseList :: String -> [Maybe Passport]
+parseList s =
+  let p = parserPassport `P.sepBy` P.endOfLine
+   in case P.parseOnly p (T.pack s) of
+        Left s -> error (show s)
+        Right r -> r
+
+day4 :: IO ()
+day4 = do
+  r <- readFile "./input/day4"
+  putStr "[Day 4-1] # trees: "
+  print . length . catMaybes . parseList $ r