Day07.hs

star2 :: [(String, [(Int, String)])] -> Int
star2 i = let m        = M.fromList i
              go n []  = n
              go n kss = let n'    =  sum . fmap fst $ kss''
                             kss'  = fmap (\(c, (c', s)) -> (c * c', s))
                                     . concatMap sequence $ kss''
                             kss'' = fmap (fmap (m M.!)) kss
                         in  go (n + n') kss'
          in go 0 [(1, "shiny gold")]

star2' :: [(String, [(Int, String)])] -> Int
star2' i = let m     = M.fromList i
               go st = case m M.! st of
                          [] -> 0
                          cs -> sum (fmap fst cs)
                                + sum (fmap (uncurry (*) . fmap go) cs)
           in go "shiny gold"