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-rw-r--r--2020/19-Monster_Messages/first.hs6
1 files changed, 3 insertions, 3 deletions
diff --git a/2020/19-Monster_Messages/first.hs b/2020/19-Monster_Messages/first.hs
index 56a0cbb..84b0aed 100644
--- a/2020/19-Monster_Messages/first.hs
+++ b/2020/19-Monster_Messages/first.hs
@@ -3,7 +3,6 @@ module Main (main) where
import Control.Monad (void, when)
import Data.Either
import Data.List (foldl')
-import Data.Maybe (isJust)
import Data.Map qualified as M
import Data.Void (Void)
import Text.Megaparsec
@@ -70,11 +69,12 @@ compute (Input rules messages) = length . filter id $ map isValid messages
Just "" -> True
otherwise -> False
matches :: RuleID -> Message -> Maybe Message
+ matches _ [] = Nothing
matches ruleId msg = case rules M.! ruleId of
Left c -> if head msg == c then (Just $ tail msg) else Nothing
Right actions -> case map (processAction msg) actions of
- Nothing:a:_ -> a
- a:_ -> a
+ Just a:_ -> Just a
+ Nothing:Just a:_ -> Just a
otherwise -> Nothing
processAction :: Message -> Action -> Maybe Message
processAction msg action = foldl' step (Just msg) action