2nd part

2020/7-2.hs

@@ -0,0 +1,48 @@
+import Text.Parsec
+import Text.Parsec.Char
+import Data.List
+
+contain
+  = do { num <- many1 digit;
+         many1 space;
+         x <- many1 letter;
+         many1 space;
+         y <- many1 letter;
+         many1 space;
+         if num == "1" then
+           string "bag"
+         else
+           string "bags";
+         return (x ++ " " ++ y, read num :: Integer);
+       }
+
+line
+  = do { x <- many1 letter;
+         many1 space;
+         y <- many1 letter;
+         many1 space;
+         string "bags contain";
+         many1 space;
+         z <- do { rcar <- contain;
+                   rcdr <- many $ (string "," >> many space >> contain);
+                   return $ rcar:rcdr;
+                 } <|> (string "no other bags" >> return []);
+         char '.';
+         return (x ++ " " ++ y, z)
+       }
+
+p
+  = many1 $ line >>= \x -> many1 space >> return x
+
+calc :: [(String, [(String, Integer)])]
+     -> String
+     -> Integer
+calc dict target
+  = case lookup target dict of
+      Just lst -> sum $ map (\(s, i) -> i + i * calc dict s) lst
+      Nothing -> error ""
+
+main
+  = readFile "7" >>= \x -> putStrLn $ case runParser p () "7" x of
+                                        Left err -> show err
+                                        Right x -> show $ calc x "shiny gold"