day10: cleanup

- use elem instad of a massive chain of ||
- add explicit error cases

2021/day10.hs

@@ -2,18 +2,21 @@ module Day10 where
 
 import Data.Maybe
 import Data.List (sort)
+import Control.Monad (foldM)
+
 closing :: Char -> Char
 closing '(' = ')'
 closing '[' = ']'
 closing '{' = '}'
 closing '<' = '>'
+closing _ = error "Not a bracket"
 
-score :: Char -> Int
+score :: Char -> Maybe Int
-score ' ' = 0
+score ')' = Just 3
-score ')' = 3
+score ']' = Just 57
-score ']' = 57
+score '}' = Just 1197
-score '}' = 1197
+score '>' = Just 25137
-score '>' = 25137
+score _ = Nothing
 
 closingScore :: Char -> Int
 closingScore ')' = 1
@@ -28,13 +31,13 @@ calcScore xs = foldr (\char score -> score*5 + closingScore char) 0 (reverse xs)
 getInvalidChar :: [Char] -> String -> Char
 getInvalidChar _ [] = ' '
 getInvalidChar st (x:xs)
-    | x == '(' || x == '[' || x == '{' || x == '<' = getInvalidChar (x:st) xs
+    | x `elem` "([{<" = getInvalidChar (x:st) xs
     | otherwise = if Just x == fmap closing (listToMaybe st) then getInvalidChar (tail st) xs else x
 
 getCompletionString :: [Char] -> String -> String
 getCompletionString st [] = map closing st
 getCompletionString st (x:xs)
-    | x == '(' || x == '[' || x == '{' || x == '<' = getCompletionString (x:st) xs
+    | x `elem` "([{<" = getCompletionString (x:st) xs
     | otherwise = if Just x == fmap closing (listToMaybe st) then getCompletionString (tail st) xs else ""
 
 
@@ -43,7 +46,7 @@ main = do
     input <- lines <$> getContents
 
     putStr "part 1: "
-    let chars = map (score . getInvalidChar []) input
+    let chars = mapMaybe (score . getInvalidChar []) input
     print $ sum chars
 
     putStr "part 2: "