an example algebraic data type for a history event

HistoryADT.hs

data HistoryEvent = Play
                        { tilesPlaced :: [Positioned LetterTile]
                        , wordsFormed :: [[Letter]]
                        , rawPoints :: Int
                        , pointsAfterSpecialTile :: Int
                        }
                  | Challenge { invalidWords :: [[Letter]] }
                  | Exchange { old :: [LetterTile], new :: [LetterTile] }
                  | Pass

-- In our GUI implementation,
-- this would be "update a sidebar" or something.
process :: Player -> HistoryEvent -> IO ()
process player (Play tp wf rp past) = do
    putStrLn $ "Player " ++ show player ++ " played a word!"
    putStrLn $ "The tiles were " ++ show tp ++ ","
    putStrLn $ "and the words formed were: " ++ show wf ++ "."
    putStrLn $ "Before special tiles were applied, "
    putStrLn $ "this play was worth " ++ show rp ++ " point(s);"
    putStrLn $ "after special tiles,"
    putStrLn $ "it was worth " ++ show past ++ " point(s)."
process player (Challenge invs) = do
    putStrLn $ "Player " ++ show player ++ " challenged!"
    case invs of
        [] -> putStrLn $ "It was unsuccessful, though."
        _ -> putStrLn $ "It worked! These words were invalid: " ++ show invs
process player (Exchange old _) = do
    putStrLn $ "Player " ++ show player ++ " exchanged tiles!"
    putStrLn $ "The tiles themselves are secret,"
    putStrLn $
        "but the player exchanged exactly " ++ show (length old) ++ " of them."
process player Pass = putStrLn $ "Player " ++ show player ++ " passed."