Solve day 6, parts 1 and 2

AdventOfCode2020.cabal

@@ -17,7 +17,7 @@ maintainer:          gael@depreeuw.dev
 extra-source-files:  CHANGELOG.md, README.md
 
 library
-  exposed-modules:     Day1, Day2, Day3, Day4, Day5
+  exposed-modules:     Day1, Day2, Day3, Day4, Day5, Day6
   -- other-modules:
   -- other-extensions:
   build-depends:       base ^>=4.13.0.0

Main.hs

@@ -5,6 +5,7 @@ import Day2 (day2)
 import Day3 (day3)
 import Day4 (day4)
 import Day5 (day5)
+import Day6 (day6)
 
 main :: IO ()
 main = do
@@ -13,3 +14,4 @@ main = do
   day3
   day4
   day5
+  day6

src/Day6.hs

@@ -0,0 +1,27 @@
+module Day6 (day6) where
+
+import Data.List (foldl', intersect)
+import qualified Data.Set as S
+
+separateForms :: [String] -> [[String]]
+separateForms s = let (a, b) = foldl' go ([], []) s in b ++ [a]
+  where
+    go (l, t) "" = ([], t ++ [l])
+    go (l, t) xs = (l ++ [xs], t)
+
+countYesses :: [String] -> Int
+countYesses = length . S.fromList . concat
+
+countYesses' :: [String] -> Int
+countYesses' = length . foldl' go ['a' .. 'z']
+  where
+    go b a = b `intersect` a
+
+day6 :: IO ()
+day6 = do
+  r <- readFile "./input/day6"
+  let m = separateForms . lines $ r
+  putStr "[Day 6-1] # yess: "
+  print . sum . map countYesses $ m
+  putStr "[Day 6-2] # yess: "
+  print . sum . map countYesses' $ m