why the f is it not working???

aoc2023.cabal

@@ -382,6 +382,8 @@ executable day23
 
 executable day24
   main-is: Day24.hs
+  other-modules:
+      Util.Parser
   hs-source-dirs:
       src
   ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -main-is Day24
@@ -464,6 +466,7 @@ test-suite spec
       TestDay21
       TestDay22
       TestDay23
+      TestDay24
       Paths_aoc2023
   autogen-modules:
       Paths_aoc2023

package.yaml

@@ -150,7 +150,7 @@ executables:
   day24:
     source-dirs:     src
     main:            Day24
-    other-modules:   []
+    other-modules:   [Util.Parser]
 
   day25:
     source-dirs:     src

src/Day24.hs

@@ -1,7 +1,66 @@
 module Day24 (main, part1, part2) where
 
+import Util.Parser (Parser, parse)
+import qualified Text.Parsec as P
+
+type Vec2 = (Double, Double)
+type Vec3 = (Double, Double, Double)
+type Particle2D = (Vec2, Vec2)
+type Particle3D = (Vec3, Vec3)
+
+dropZ :: Particle3D -> Particle2D
+dropZ ((x, y, _), (dx, dy, _)) = ((x, y), (dx, dy))
+
+negP :: Parser Double
+negP = negate . read <$> (P.char '-' *> P.many1 P.digit)
+
+posP :: Parser Double
+posP = read <$> P.many1 P.digit
+
+numP :: Parser Double
+numP = negP P.<|> posP
+
+vec3P :: Parser Vec3
+vec3P = do
+  x <- numP <* P.char ',' <* P.spaces
+  y <- numP <* P.char ',' <* P.spaces
+  z <- numP
+  return (x, y, z)
+
+particleP :: Parser Particle3D
+particleP = do
+  p <- vec3P <* P.spaces <* P.char '@' <* P.spaces
+  v <- vec3P
+  return (p, v)
+
+inputP :: Parser [Particle3D]
+inputP = P.many1 (particleP <* P.spaces) <* P.eof
+
+border :: (Num a, Ord a) => a -> Bool
+border x = 200000000000000 <= x && x <= 400000000000000
+
+det :: Vec2 -> Vec2 -> Double
+det (x1, y1) (x2, y2) = x1 * y2 - x2 * y1
+
+intersect2D :: Particle2D -> Particle2D -> Bool
+intersect2D ((x1, y1), (dx1, dy1)) ((x2, y2), (dx2, dy2)) =
+    let xd = (-dx1, -dx2)
+        yd = (-dy1, -dy2)
+        dv = det xd yd
+        d = (det (x1, y1) (x1 + dx1, y1 + dy1), det (x2, y2) (x2 + dx2, y2 + dy2))
+        x = det d xd / dv
+        y = det d yd / dv
+    in
+        dv /= 0 &&
+        (x - x1 > 0) == (dx1 > 0) && (y - y1 > 0) == (dy1 > 0) &&
+        (x - x2 > 0) == (dx2 > 0) && (y - y2 > 0) == (dy2 > 0) &&
+        border x && border y
+
+solution :: [Particle2D] -> Int
+solution particles = length $ filter (uncurry intersect2D) [(p1, p2) | p1 <- particles, p2 <- particles, p1 /= p2]
+
 part1 :: String -> String
-part1 = id
+part1 = show . solution . map dropZ . parse inputP
 
 part2 :: String -> String
 part2 = const ""

test/Main.hs

@@ -23,6 +23,7 @@ import TestDay20
 import TestDay21
 import TestDay22
 import TestDay23
+import TestDay24
 
 main :: IO ()
 main = do
@@ -49,3 +50,4 @@ main = do
     TestDay21.test
     TestDay22.test
     TestDay23.test
+    TestDay24.test

test/TestDay24.hs

@@ -0,0 +1,23 @@
+module TestDay24 (test) where
+
+import Day24
+import Test.Hspec
+
+input :: String
+input = "19, 13, 30 @ -2,  1, -2\n18, 19, 22 @ -1, -1, -2\n20, 25, 34 @ -2, -2, -4\n12, 31, 28 @ -1, -2, -1\n20, 19, 15 @  1, -5, -3"
+
+test1 :: Expectation
+test1 = part1 input `shouldBe` "2"
+
+test2 :: Expectation
+test2 = part2 input `shouldBe` ""
+
+test :: IO ()
+test = hspec $ do
+    describe "day24" $ do
+        describe "part1" $ do
+            it "should work for the examples" test1
+
+        describe "part2" $ do
+            it "should work for the examples" test2
+