day4,5: update - use parser combinators

not the cleanest, im still learning parsing in hs

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

day4.hs

@@ -1,29 +1,34 @@
-import Lib (split)
+import Data.Char (isDigit)
+import Text.ParserCombinators.ReadP
+  ( ReadP,
+    char,
+    many1,
+    readP_to_S,
+    satisfy,
+  )
 
 main :: IO ()
 main = do
-  input <- readFile "day4.in"
+  input <- map (fst . last . readP_to_S parse) . lines <$> readFile "day4.in"
   putStr "Q1: "
   print $ q1 input
   putStr "Q2: "
   print $ q2 input
 
-q1 :: String -> Int
-q1 =
-  length
-    . filter
-      ( \x ->
-          let [[a, b], [c, d]] = map (map (read :: String -> Int) . split '-') $ split ',' x
-           in a >= c && b <= d || c >= a && d <= b
-      )
-    . lines
+parse :: ReadP ((Int, Int), (Int, Int))
+parse = do
+  a <- readInt
+  char '-'
+  b <- readInt
+  char ','
+  c <- readInt
+  char '-'
+  d <- readInt
+  return ((a, b), (c, d))
+  where
+    readInt :: ReadP Int
+    readInt = read <$> many1 (satisfy isDigit)
 
-q2 :: String -> Int
-q2 =
-  length
-    . filter
-      ( \x ->
-          let [[a, b], [c, d]] = map (map (read :: String -> Int) . split '-') $ split ',' x
-           in b >= c && a <= d || d >= a && c <= b
-      )
-    . lines
+q1, q2 :: [((Int, Int), (Int, Int))] -> Int
+q1 = length . filter (\((a, b), (c, d)) -> a >= c && b <= d || c >= a && d <= b)
+q2 = length . filter (\((a, b), (c, d)) -> b >= c && a <= d)