Day 9 - alternate solution using only one foldl pass

9_alt.hs

@@ -0,0 +1,16 @@
+scoreAndCount :: String -> (Int, Int)
+scoreAndCount str =
+    let (_, _, _, score, count) = foldl f (False, False, 1, 0, 0) str
+    in  (score, count)
+    where f (isCancel, isGarbage, level, score, count) curr
+            | isCancel    = (False,       isGarbage,   level,     score,         count)
+            | isGarbage   = (curr == '!', curr /= '>', level,     score,         count + (fromEnum $ curr /= '>' && curr /= '!'))
+            | curr == '{' = (False,       False,       level + 1, score + level, count)
+            | curr == '}' = (False,       False,       level - 1, score,         count)
+            | curr == ',' = (False,       False,       level,     score,         count)
+            | curr == '<' = (False,       True,        level,     score,         count)
+
+main :: IO ()
+main = do
+    input <- readFile "9.txt"
+    print $ scoreAndCount input